neuron-web/runtime/el_runtime.c

/*
 * el_runtime.c — El language C runtime implementation
 *
 * All functions use el_val_t (= int64_t) as the universal value type.
 * Strings are transported as their pointer address cast to int64_t.
 * On any 64-bit system sizeof(pointer) <= sizeof(int64_t), so this is safe.
 *
 * Compile with:
 *   cc -std=c11 -I<runtime-dir> -lcurl -lpthread -o <prog> <prog>.c el_runtime.c
 *
 * Link requirements: -lcurl (HTTP client + LLM), -lpthread (HTTP server).
 */

/* Feature-test macros must be set before any standard headers. _GNU_SOURCE
 * exposes clock_gettime/CLOCK_REALTIME, strcasecmp, and the dlfcn extensions
 * (RTLD_DEFAULT) — all of which macOS hands us without asking but glibc on
 * Debian gates behind an explicit opt-in.                                   */
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

#include "el_runtime.h"

#include <stdarg.h>
#include <strings.h>     /* strcasecmp */
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <math.h>
#include <time.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <dlfcn.h>      /* dlsym for http_set_handler fallback */
#include <unistd.h>
#include <fcntl.h>
#include <dirent.h>
#include <errno.h>
#include <pthread.h>
#include <sys/resource.h>  /* getrusage — memory guard */
#ifdef HAVE_CURL
#include <curl/curl.h>
#endif

/* ── Internal allocators ─────────────────────────────────────────────────── */

/*
 * Per-request string arena
 *
 * Every El string allocated via el_strbuf / el_strdup during an HTTP request
 * is registered in a thread-local arena. When el_request_end() is called at
 * the end of the worker thread, every arena entry is freed — recovering all
 * the intermediate strings from el_str_concat chains (build_system_prompt,
 * engram_compile, etc.) that are otherwise leaked forever.
 *
 * Long-lived allocations (state_set values, engram internal storage) call
 * el_strdup_persist() / el_strbuf_persist() which bypass the arena entirely.
 */

#define EL_ARENA_INITIAL 512

typedef struct {
    char**  ptrs;
    size_t  count;
    size_t  cap;
} ElArena;

static _Thread_local ElArena _tl_arena = {NULL, 0, 0};
static _Thread_local int     _tl_arena_active = 0;

/* Binary-safe fs_read length — set by fs_read, consumed by http_send_response.
 * Allows serving PNGs and other binary files without strlen truncation. */
static _Thread_local size_t  _tl_fs_read_len  = 0;

/* Binary body side-channel for http_response().
 *
 * http_response() normally JSON-encodes the body via jb_emit_escaped(), which
 * stops at the first null byte (C-string semantics). Binary files like PNGs
 * contain null bytes as early as byte 8 (IHDR chunk length), causing truncation.
 *
 * When _tl_fs_read_len > 0 at the time http_response() is called, we skip
 * JSON-encoding and instead:
 *   1. malloc-copy the raw bytes here
 *   2. write the sentinel string "__el_binary__" into the envelope body field
 *   3. In http_send_response(), detect the sentinel and use these raw bytes
 *
 * Thread-local so each worker thread has independent storage.
 * Lifecycle: set by http_response(), consumed (and freed) by http_send_response(). */
static _Thread_local char*   _tl_binary_body = NULL;
static _Thread_local size_t  _tl_binary_size = 0;

static void el_arena_track(char* p) {
    if (!_tl_arena_active || !p) return;
    if (_tl_arena.count >= _tl_arena.cap) {
        size_t nc = _tl_arena.cap == 0 ? EL_ARENA_INITIAL : _tl_arena.cap * 2;
        char** grown = realloc(_tl_arena.ptrs, nc * sizeof(char*));
        if (!grown) return; /* can't track — will leak this one ptr, but don't crash */
        _tl_arena.ptrs = grown;
        _tl_arena.cap  = nc;
    }
    _tl_arena.ptrs[_tl_arena.count++] = p;
}

/* Called by http_worker before dispatching the El handler. */
void el_request_start(void) {
    _tl_arena.count  = 0;
    _tl_arena_active = 1;
}

/* Called by http_worker after the El handler returns and the response is sent.
 * Frees every intermediate string allocated during the request. */
void el_request_end(void) {
    _tl_arena_active = 0;
    for (size_t i = 0; i < _tl_arena.count; i++) {
        free(_tl_arena.ptrs[i]);
    }
    _tl_arena.count = 0;
}

/* ── Scoped arena for CLI use ─────────────────────────────────────────────── *
 * CLI programs never call el_request_start/end, so all strdup allocations are
 * permanent. el_arena_push/pop let the compiler free intermediate strings
 * after each compilation unit.
 *
 * el_arena_push() — activates the arena if not already active, saves the
 *   current arena count as a mark, and returns it as an el_val_t Int.
 * el_arena_pop(mark) — frees all strings allocated since the push mark and
 *   resets the count. If count reaches 0, deactivates the arena.
 */
#define EL_ARENA_SCOPE_DEPTH 32
static _Thread_local size_t  _tl_arena_scope[EL_ARENA_SCOPE_DEPTH];
static _Thread_local int     _tl_arena_scope_depth = 0;

el_val_t el_arena_push(void) {
    if (!_tl_arena_active) {
        _tl_arena_active = 1;
    }
    if (_tl_arena_scope_depth < EL_ARENA_SCOPE_DEPTH) {
        _tl_arena_scope[_tl_arena_scope_depth++] = _tl_arena.count;
    }
    return (el_val_t)(int64_t)_tl_arena.count;
}

el_val_t el_arena_pop(el_val_t mark) {
    size_t save = (size_t)(int64_t)mark;
    if (save > _tl_arena.count) save = 0;
    for (size_t i = save; i < _tl_arena.count; i++) {
        if (_tl_arena.ptrs[i]) {
            free(_tl_arena.ptrs[i]);
            _tl_arena.ptrs[i] = NULL;
        }
    }
    _tl_arena.count = save;
    if (_tl_arena_scope_depth > 0) _tl_arena_scope_depth--;
    if (save == 0) _tl_arena_active = 0;
    return 0;
}

/* Persistent allocation — bypasses the arena (state_set, engram internals). */
static char* el_strdup_persist(const char* s) {
    if (!s) return strdup("");
    return strdup(s);
}
static char* el_strbuf_persist(size_t n) {
    char* p = malloc(n + 1);
    if (!p) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    p[0] = '\0';
    return p;
}

static char* el_strdup(const char* s) {
    if (!s) { char* p = strdup(""); el_arena_track(p); return p; }
    char* p = strdup(s);
    el_arena_track(p);
    return p;
}

static char* el_strbuf(size_t n) {
    char* p = malloc(n + 1);
    if (!p) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    p[0] = '\0';
    el_arena_track(p);
    return p;
}

/* Wrap an allocated C string as el_val_t */
static el_val_t el_wrap_str(char* s) {
    return EL_STR(s);
}

/* ── I/O ──────────────────────────────────────────────────────────────────── */

el_val_t println(el_val_t s) {
    const char* str = EL_CSTR(s);
    if (str) puts(str);
    else     puts("");
    return 0;
}

el_val_t print(el_val_t s) {
    const char* str = EL_CSTR(s);
    if (str) fputs(str, stdout);
    return 0;
}

el_val_t readline(void) {
    char buf[4096];
    if (!fgets(buf, sizeof(buf), stdin)) return el_wrap_str(el_strdup(""));
    size_t len = strlen(buf);
    if (len > 0 && buf[len - 1] == '\n') buf[len - 1] = '\0';
    return el_wrap_str(el_strdup(buf));
}

/* __read_n — read exactly n bytes from stdin.
 * Allocates a buffer of size n+1, calls fread(buf, 1, n, stdin) to read
 * exactly n raw bytes (including \r, \n, NUL, etc.), null-terminates, and
 * returns the buffer as an El String.  Returns "" on EOF or I/O error.
 *
 * Used by the El LSP server to read JSON-RPC message bodies after parsing
 * the Content-Length header.  readline() cannot be used for the body because
 * it stops at the first \n and LSP JSON bodies are not newline-terminated.  */
el_val_t __read_n(el_val_t nv) {
    int64_t n = EL_INT(nv);
    if (n <= 0) return el_wrap_str(el_strdup(""));
    char* buf = malloc((size_t)n + 1);
    if (!buf) { fputs("el_runtime: __read_n: out of memory\n", stderr); return el_wrap_str(el_strdup("")); }
    size_t got = fread(buf, 1, (size_t)n, stdin);
    buf[got] = '\0';
    if (got == 0) { free(buf); return el_wrap_str(el_strdup("")); }
    /* Track in arena so the allocation is freed when the request ends. */
    el_arena_track(buf);
    return el_wrap_str(buf);
}

/* __print_raw — write a string to stdout without any modification.
 * Unlike println/print (which call puts/fputs and may add newlines or flush
 * in platform-specific ways), this uses fwrite with the exact byte count so
 * that embedded \r\n pairs in LSP Content-Length headers survive intact.    */
void __print_raw(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return;
    size_t len = strlen(s);
    fwrite(s, 1, len, stdout);
    fflush(stdout);
}

/* ── String builtins ─────────────────────────────────────────────────────── */

el_val_t el_str_concat(el_val_t av, el_val_t bv) {
    const char* a = EL_CSTR(av);
    const char* b = EL_CSTR(bv);
    if (!a) a = "";
    if (!b) b = "";
    size_t la = strlen(a);
    size_t lb = strlen(b);
    char* out = el_strbuf(la + lb);
    memcpy(out, a, la);
    memcpy(out + la, b, lb);
    out[la + lb] = '\0';
    return el_wrap_str(out);
}

el_val_t str_eq(el_val_t av, el_val_t bv) {
    const char* a = EL_CSTR(av);
    const char* b = EL_CSTR(bv);
    if (!a || !b) return (el_val_t)(a == b);
    return (el_val_t)(strcmp(a, b) == 0);
}

el_val_t str_starts_with(el_val_t sv, el_val_t prefv) {
    const char* s      = EL_CSTR(sv);
    const char* prefix = EL_CSTR(prefv);
    if (!s || !prefix) return 0;
    size_t lp = strlen(prefix);
    return (el_val_t)(strncmp(s, prefix, lp) == 0);
}

el_val_t str_ends_with(el_val_t sv, el_val_t sufv) {
    const char* s      = EL_CSTR(sv);
    const char* suffix = EL_CSTR(sufv);
    if (!s || !suffix) return 0;
    size_t ls   = strlen(s);
    size_t lsuf = strlen(suffix);
    if (lsuf > ls) return 0;
    return (el_val_t)(strcmp(s + ls - lsuf, suffix) == 0);
}

el_val_t str_len(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return 0;
    return (el_val_t)strlen(s);
}

el_val_t str_concat(el_val_t a, el_val_t b) {
    return el_str_concat(a, b);
}

el_val_t int_to_str(el_val_t n) {
    char buf[32];
    snprintf(buf, sizeof(buf), "%lld", (long long)n);
    return el_wrap_str(el_strdup(buf));
}

el_val_t str_to_int(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return 0;
    return (el_val_t)atoll(s);
}

/* native_str_to_int — El compiler-generated alias for str_to_int.
 * Converts a string el_val_t to its integer representation. */
el_val_t native_str_to_int(el_val_t sv) { return str_to_int(sv); }

el_val_t str_slice(el_val_t sv, el_val_t start, el_val_t end) {
    const char* s = EL_CSTR(sv);
    if (!s) return el_wrap_str(el_strdup(""));
    int64_t len = (int64_t)strlen(s);
    if (start < 0) start = 0;
    if (end > len) end = len;
    if (start >= end) return el_wrap_str(el_strdup(""));
    int64_t sz = end - start;
    char* out = el_strbuf((size_t)sz);
    memcpy(out, s + start, (size_t)sz);
    out[sz] = '\0';
    return el_wrap_str(out);
}

el_val_t str_contains(el_val_t sv, el_val_t subv) {
    const char* s   = EL_CSTR(sv);
    const char* sub = EL_CSTR(subv);
    if (!s || !sub) return 0;
    return (el_val_t)(strstr(s, sub) != NULL);
}

el_val_t str_replace(el_val_t sv, el_val_t fromv, el_val_t tov) {
    const char* s    = EL_CSTR(sv);
    const char* from = EL_CSTR(fromv);
    const char* to   = EL_CSTR(tov);
    if (!s || !from || !to) return el_wrap_str(el_strdup(s ? s : ""));
    size_t ls = strlen(s);
    size_t lf = strlen(from);
    size_t lt = strlen(to);
    if (lf == 0) return el_wrap_str(el_strdup(s));
    size_t count = 0;
    const char* p = s;
    while ((p = strstr(p, from)) != NULL) { count++; p += lf; }
    size_t out_sz = ls + count * lt + 1;
    char* out = el_strbuf(out_sz);
    char* dst = out;
    p = s;
    const char* found;
    while ((found = strstr(p, from)) != NULL) {
        size_t chunk = (size_t)(found - p);
        memcpy(dst, p, chunk); dst += chunk;
        memcpy(dst, to, lt);  dst += lt;
        p = found + lf;
    }
    strcpy(dst, p);
    return el_wrap_str(out);
}

el_val_t str_to_upper(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return el_wrap_str(el_strdup(""));
    size_t n = strlen(s);
    char* out = el_strbuf(n);
    for (size_t i = 0; i < n; i++) out[i] = (char)toupper((unsigned char)s[i]);
    out[n] = '\0';
    return el_wrap_str(out);
}

el_val_t str_to_lower(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return el_wrap_str(el_strdup(""));
    size_t n = strlen(s);
    char* out = el_strbuf(n);
    for (size_t i = 0; i < n; i++) out[i] = (char)tolower((unsigned char)s[i]);
    out[n] = '\0';
    return el_wrap_str(out);
}

el_val_t str_trim(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return el_wrap_str(el_strdup(""));
    while (*s && isspace((unsigned char)*s)) s++;
    size_t n = strlen(s);
    while (n > 0 && isspace((unsigned char)s[n - 1])) n--;
    char* out = el_strbuf(n);
    memcpy(out, s, n);
    out[n] = '\0';
    return el_wrap_str(out);
}

/* ── Math ────────────────────────────────────────────────────────────────── */

el_val_t el_abs(el_val_t n)             { return n < 0 ? -n : n; }
el_val_t el_max(el_val_t a, el_val_t b) { return a > b ? a : b; }
el_val_t el_min(el_val_t a, el_val_t b) { return a < b ? a : b; }

/* ── Refcounted heap objects ──────────────────────────────────────────────────
 *
 * ElList and ElMap carry a magic-tagged header at offset 0:
 *   { uint32_t magic; uint32_t refcount; ... payload ... }
 *
 * The magic tag distinguishes refcounted objects from raw C strings (whose
 * first byte is printable ASCII < 0x80) and from small integers (which can't
 * be dereferenced). el_retain / el_release sniff the magic and act only on
 * matching values; everything else is a safe no-op.
 *
 * Both ElList and ElMap use INDIRECTION: the header is fixed-size and never
 * moves. The payload arrays (elems, keys, values) live in separate heap
 * allocations, so realloc-grow on append never invalidates the caller's
 * pointer to the header. This is what lets us mutate-in-place safely when
 * the refcount is 1 and copy-on-write when it's higher.
 *
 * Memory model in practice:
 *   Single-owner accumulator (the cg_stmts pattern) — refcount stays at 1,
 *   appends amortize to O(1), total memory O(N) for an N-element list.
 *   Multi-owner branching (the cg_if_stmt pattern) — refcount > 1, each
 *   append on a shared list copies, so the original is preserved for the
 *   else-branch. Persistent semantics where they're needed; mutation where
 *   they're not.                                                              */

#define EL_MAGIC_LIST  0xE15710A1u  /* >= 0x80 in MSB so 'looks_like_string' rejects */
#define EL_MAGIC_MAP   0xE19A704Bu

typedef struct {
    uint32_t magic;
    uint32_t refcount;
} ElHeader;

/* ── List ────────────────────────────────────────────────────────────────── */

typedef struct {
    ElHeader  hdr;
    int64_t   length;
    int64_t   capacity;
    el_val_t* elems;
} ElList;

static ElList* list_alloc(int64_t cap) {
    if (cap < 4) cap = 4;
    ElList* lst = malloc(sizeof(ElList));
    if (!lst) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    lst->hdr.magic = EL_MAGIC_LIST;
    lst->hdr.refcount = 1;
    lst->length   = 0;
    lst->capacity = cap;
    lst->elems    = malloc((size_t)cap * sizeof(el_val_t));
    if (!lst->elems) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    return lst;
}

el_val_t el_list_empty(void) {
    return EL_STR(list_alloc(4));
}

el_val_t el_list_new(el_val_t count, ...) {
    ElList* lst = list_alloc(count > 0 ? count : 4);
    va_list ap;
    va_start(ap, count);
    for (int64_t i = 0; i < count; i++) {
        lst->elems[i] = va_arg(ap, el_val_t);
    }
    va_end(ap);
    lst->length = count;
    return EL_STR(lst);
}

el_val_t el_list_len(el_val_t listv) {
    ElList* lst = (ElList*)(uintptr_t)listv;
    if (!lst) return 0;
    return lst->length;
}

el_val_t el_list_get(el_val_t listv, el_val_t index) {
    ElList* lst = (ElList*)(uintptr_t)listv;
    if (!lst) return 0;
    if (index < 0 || index >= lst->length) return 0;
    return lst->elems[index];
}

el_val_t el_list_append(el_val_t listv, el_val_t elem) {
    ElList* old = (ElList*)(uintptr_t)listv;
    if (!old) {
        ElList* fresh = list_alloc(4);
        fresh->elems[0] = elem;
        fresh->length = 1;
        return EL_STR(fresh);
    }

    /* Uniquely owned: grow the elems buffer in place. The header pointer the
     * caller holds doesn't move (we only realloc the inner array). This is
     * the common case in compiler accumulators, and it's amortized O(1). */
    if (old->hdr.refcount <= 1) {
        if (old->length >= old->capacity) {
            int64_t new_cap = old->capacity > 0 ? old->capacity * 2 : 4;
            el_val_t* grown = realloc(old->elems, (size_t)new_cap * sizeof(el_val_t));
            if (!grown) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
            old->elems    = grown;
            old->capacity = new_cap;
        }
        old->elems[old->length++] = elem;
        return listv;
    }

    /* Shared: copy-on-write. The original is preserved for its other owners. */
    int64_t new_cap = old->length + 1;
    if (new_cap < 4) new_cap = 4;
    ElList* fresh = malloc(sizeof(ElList));
    if (!fresh) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    fresh->hdr.magic    = EL_MAGIC_LIST;
    fresh->hdr.refcount = 1;
    fresh->length       = old->length + 1;
    fresh->capacity     = new_cap;
    fresh->elems        = malloc((size_t)new_cap * sizeof(el_val_t));
    if (!fresh->elems) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    if (old->length > 0) {
        memcpy(fresh->elems, old->elems, (size_t)old->length * sizeof(el_val_t));
    }
    fresh->elems[old->length] = elem;
    return EL_STR(fresh);
}

el_val_t el_list_clone(el_val_t listv) {
    /* Shallow copy: the new ElList owns its own header and elems buffer, but
     * the elements themselves are shared (which is what callers want for the
     * cg_if_stmt 'declared' pattern — cloning the spine, not its contents).
     * Used by codegen at scope branch points where two child scopes need to
     * see the same starting set of declared names without each other's
     * mutations.                                                              */
    ElList* old = (ElList*)(uintptr_t)listv;
    if (!old) return el_list_empty();
    int64_t cap = old->capacity > 0 ? old->capacity : 4;
    if (cap < old->length) cap = old->length;
    if (cap < 4) cap = 4;
    ElList* fresh = malloc(sizeof(ElList));
    if (!fresh) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    fresh->hdr.magic    = EL_MAGIC_LIST;
    fresh->hdr.refcount = 1;
    fresh->length       = old->length;
    fresh->capacity     = cap;
    fresh->elems        = malloc((size_t)cap * sizeof(el_val_t));
    if (!fresh->elems) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    if (old->length > 0) {
        memcpy(fresh->elems, old->elems, (size_t)old->length * sizeof(el_val_t));
    }
    return EL_STR(fresh);
}

/* ── Map ─────────────────────────────────────────────────────────────────── */

typedef struct {
    ElHeader  hdr;
    int64_t   count;
    int64_t   capacity;
    el_val_t* keys;
    el_val_t* values;
} ElMap;

static ElMap* map_alloc(int64_t cap) {
    if (cap < 4) cap = 4;
    ElMap* m = malloc(sizeof(ElMap));
    if (!m) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    m->hdr.magic    = EL_MAGIC_MAP;
    m->hdr.refcount = 1;
    m->count        = 0;
    m->capacity     = cap;
    m->keys         = malloc((size_t)cap * sizeof(el_val_t));
    m->values       = malloc((size_t)cap * sizeof(el_val_t));
    if (!m->keys || !m->values) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    return m;
}

el_val_t el_map_new(el_val_t pair_count, ...) {
    ElMap* m = map_alloc(pair_count > 0 ? pair_count : 4);
    va_list ap;
    va_start(ap, pair_count);
    for (int64_t i = 0; i < pair_count; i++) {
        m->keys[i]   = va_arg(ap, el_val_t);
        m->values[i] = va_arg(ap, el_val_t);
    }
    va_end(ap);
    m->count = pair_count;
    return EL_STR(m);
}

static ElMap* as_map(el_val_t v) { return (ElMap*)(uintptr_t)v; }

el_val_t el_map_get(el_val_t mapv, el_val_t keyv) {
    ElMap* m = as_map(mapv);
    const char* key = EL_CSTR(keyv);
    if (!m || !key) return 0;
    for (int64_t i = 0; i < m->count; i++) {
        const char* k = EL_CSTR(m->keys[i]);
        if (k && strcmp(k, key) == 0) return m->values[i];
    }
    return 0;
}

el_val_t el_get_field(el_val_t mapv, el_val_t keyv) {
    return el_map_get(mapv, keyv);
}

/* Internal: in-place set on a uniquely-owned map. */
static el_val_t map_set_in_place(ElMap* m, el_val_t keyv, el_val_t value) {
    const char* key = EL_CSTR(keyv);
    if (key) {
        for (int64_t i = 0; i < m->count; i++) {
            const char* k = EL_CSTR(m->keys[i]);
            if (k && strcmp(k, key) == 0) { m->values[i] = value; return EL_STR(m); }
        }
    }
    if (m->count >= m->capacity) {
        int64_t new_cap = m->capacity > 0 ? m->capacity * 2 : 4;
        el_val_t* gk = realloc(m->keys,   (size_t)new_cap * sizeof(el_val_t));
        el_val_t* gv = realloc(m->values, (size_t)new_cap * sizeof(el_val_t));
        if (!gk || !gv) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
        m->keys     = gk;
        m->values   = gv;
        m->capacity = new_cap;
    }
    m->keys[m->count]   = keyv;
    m->values[m->count] = value;
    m->count++;
    return EL_STR(m);
}

el_val_t el_map_set(el_val_t mapv, el_val_t keyv, el_val_t value) {
    ElMap* m = as_map(mapv);
    if (!m) return 0;
    if (m->hdr.refcount <= 1) {
        return map_set_in_place(m, keyv, value);
    }
    /* Shared: copy then set. The original is preserved for its other owners. */
    int64_t new_cap = m->count + 1;
    if (new_cap < 4) new_cap = 4;
    ElMap* fresh = malloc(sizeof(ElMap));
    if (!fresh) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    fresh->hdr.magic    = EL_MAGIC_MAP;
    fresh->hdr.refcount = 1;
    fresh->count        = m->count;
    fresh->capacity     = new_cap;
    fresh->keys         = malloc((size_t)new_cap * sizeof(el_val_t));
    fresh->values       = malloc((size_t)new_cap * sizeof(el_val_t));
    if (!fresh->keys || !fresh->values) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    if (m->count > 0) {
        memcpy(fresh->keys,   m->keys,   (size_t)m->count * sizeof(el_val_t));
        memcpy(fresh->values, m->values, (size_t)m->count * sizeof(el_val_t));
    }
    return map_set_in_place(fresh, keyv, value);
}

/* ── Refcount ops ─────────────────────────────────────────────────────────── */
/*
 * Both retain and release sniff the magic header to decide whether a value
 * is a refcounted heap object. For small integers, raw C strings, and any
 * value whose magic word doesn't match, both functions are no-ops. This lets
 * codegen emit them on every let-binding without having to track types.
 *
 * Safety: we filter out obvious non-pointers (small magnitudes, misaligned
 * addresses) before dereferencing. For any value that passes the filter and
 * lives in a mapped page, reading the first 4 bytes is safe — strings start
 * with printable ASCII (< 0x80), so their magic word will never collide with
 * EL_MAGIC_LIST (0xE1...) or EL_MAGIC_MAP (0xE1...). Random integers that
 * happen to look like aligned heap pointers are exceedingly unlikely to land
 * on a page whose first 4 bytes match either magic.                          */

static int looks_like_heap_obj(el_val_t v) {
    if (v == 0) return 0;
    int64_t s = (int64_t)v;
    if (s > -0x10000 && s < 0x10000) return 0;     /* small ints */
    uintptr_t p = (uintptr_t)v;
    if (p < 0x10000) return 0;                      /* low addresses */
    if (p & 0x7) return 0;                          /* malloc returns 8-aligned */
    return 1;
}

void el_retain(el_val_t v) {
    if (!looks_like_heap_obj(v)) return;
    ElHeader* h = (ElHeader*)(uintptr_t)v;
    if (h->magic == EL_MAGIC_LIST || h->magic == EL_MAGIC_MAP) {
        h->refcount++;
    }
}

void el_release(el_val_t v) {
    if (!looks_like_heap_obj(v)) return;
    ElHeader* h = (ElHeader*)(uintptr_t)v;
    if (h->magic == EL_MAGIC_LIST) {
        if (h->refcount > 0 && --h->refcount == 0) {
            ElList* l = (ElList*)h;
            free(l->elems);
            l->hdr.magic = 0;   /* poison so use-after-free is detected */
            free(l);
        }
    } else if (h->magic == EL_MAGIC_MAP) {
        if (h->refcount > 0 && --h->refcount == 0) {
            ElMap* m = (ElMap*)h;
            free(m->keys);
            free(m->values);
            m->hdr.magic = 0;
            free(m);
        }
    }
}

/* ── Batch 2/3 forward decls (defined later in JSON section) ────────────── */

typedef struct JsonBuf JsonBuf;
typedef struct JsonParser JsonParser;
static void jb_init(JsonBuf* b);
static void jb_putc(JsonBuf* b, char c);
static void jb_puts(JsonBuf* b, const char* s);
static void jb_emit_escaped(JsonBuf* b, const char* s);
static int  looks_like_string(el_val_t v);
static const char* json_find_key(const char* s, const char* key);
static const char* json_skip_value(const char* p);
static char* jp_parse_string_raw(JsonParser* jp);

/* Struct definitions are visible here because batch 2/3 helpers above use
 * them by value; the bodies (jb_init, etc.) appear in the JSON section. */
struct JsonBuf {
    char*  buf;
    size_t len;
    size_t cap;
};

struct JsonParser {
    const char* p;
    const char* end;
    int         err;
};

/* ── Batch 2: Real HTTP (libcurl client + POSIX-socket server) ───────────── */
/*
 * Client: blocking libcurl easy-handle calls. Errors are returned as a JSON
 * fragment {"error":"..."} so callers can detect via str_starts_with("{") /
 * json_get_string("error", ...).
 *
 * Server: bind/listen/accept loop on a TCP socket. Each accepted connection
 * is handled in its own pthread (detached). A semaphore-style counter caps
 * concurrent in-flight connections at HTTP_MAX_CONNS (64). When the cap is
 * reached, accept() blocks until a worker exits. This prevents runaway
 * thread creation under high load.
 *
 * Handler dispatch: El does not expose first-class function references at
 * the runtime layer, so the second argument to http_serve(port, handler) is
 * treated as a string name (or any el_val_t — the runtime ignores its
 * value and uses the registry). Callers register a C-level handler via
 *
 *     extern void el_runtime_register_handler(const char* name,
 *                                              el_val_t (*fn)(el_val_t,
 *                                                             el_val_t,
 *                                                             el_val_t));
 *
 * and select the active handler by calling http_set_handler("name") from
 * El, or by setting it directly through the C registry. If no handler is
 * registered, the server replies with a 200 carrying a default message so
 * the loop is observable.
 */

/* ── JSON error helper (used by HTTP, PQ, crypto stubs) ─────────────────── */

/* JSON-escape an arbitrary C string into an allocated buffer. */
static char* json_escape_alloc(const char* s) {
    if (!s) return el_strdup("");
    JsonBuf b; jb_init(&b);
    for (const char* p = s; *p; p++) {
        unsigned char c = (unsigned char)*p;
        switch (c) {
            case '"':  jb_puts(&b, "\\\""); break;
            case '\\': jb_puts(&b, "\\\\"); break;
            case '\n': jb_puts(&b, "\\n");  break;
            case '\r': jb_puts(&b, "\\r");  break;
            case '\t': jb_puts(&b, "\\t");  break;
            default:
                if (c < 0x20) {
                    char tmp[8]; snprintf(tmp, sizeof(tmp), "\\u%04x", c);
                    jb_puts(&b, tmp);
                } else jb_putc(&b, (char)c);
        }
    }
    return b.buf;
}

static el_val_t http_error_json(const char* msg) {
    char* esc = json_escape_alloc(msg ? msg : "unknown error");
    char* buf = el_strbuf(strlen(esc) + 16);
    sprintf(buf, "{\"error\":\"%s\"}", esc);
    free(esc);
    return el_wrap_str(buf);
}

#ifdef HAVE_CURL
/* ── HTTP client write-callback buffer ───────────────────────────────────── */

typedef struct {
    char*  data;
    size_t len;
    size_t cap;
} HttpBuf;

static void httpbuf_init(HttpBuf* b) {
    b->cap = 1024;
    b->len = 0;
    b->data = malloc(b->cap);
    if (!b->data) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    b->data[0] = '\0';
}

static void httpbuf_append(HttpBuf* b, const void* src, size_t n) {
    if (b->len + n + 1 > b->cap) {
        while (b->len + n + 1 > b->cap) b->cap *= 2;
        b->data = realloc(b->data, b->cap);
        if (!b->data) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    }
    memcpy(b->data + b->len, src, n);
    b->len += n;
    b->data[b->len] = '\0';
}

static size_t http_write_cb(char* ptr, size_t size, size_t nmemb, void* ud) {
    size_t n = size * nmemb;
    httpbuf_append((HttpBuf*)ud, ptr, n);
    return n;
}

/* HTTP timeout (ms) — read once from EL_HTTP_TIMEOUT_MS, default 60000.
 * Applied via CURLOPT_TIMEOUT_MS on every libcurl request. */
static long _el_http_timeout_ms = -1;
static long el_http_timeout_ms(void) {
    long v = __atomic_load_n(&_el_http_timeout_ms, __ATOMIC_ACQUIRE);
    if (v >= 0) return v;
    const char* s = getenv("EL_HTTP_TIMEOUT_MS");
    long parsed = 60000L;
    if (s && *s) {
        char* end = NULL;
        long n = strtol(s, &end, 10);
        if (end != s && n > 0) parsed = n;
    }
    __atomic_store_n(&_el_http_timeout_ms, parsed, __ATOMIC_RELEASE);
    return parsed;
}

/* Internal: do a libcurl request; takes optional body/headers, optional method override. */
static el_val_t http_do(const char* method, const char* url, const char* body,
                        struct curl_slist* extra_headers) {
    if (!url || !*url) return http_error_json("empty url");
    CURL* c = curl_easy_init();
    if (!c) return http_error_json("curl_easy_init failed");
    HttpBuf rb; httpbuf_init(&rb);
    char errbuf[CURL_ERROR_SIZE]; errbuf[0] = '\0';
    curl_easy_setopt(c, CURLOPT_URL, url);
    curl_easy_setopt(c, CURLOPT_WRITEFUNCTION, http_write_cb);
    curl_easy_setopt(c, CURLOPT_WRITEDATA, &rb);
    curl_easy_setopt(c, CURLOPT_FOLLOWLOCATION, 1L);
    curl_easy_setopt(c, CURLOPT_TIMEOUT_MS, el_http_timeout_ms());
    curl_easy_setopt(c, CURLOPT_NOSIGNAL, 1L);
    curl_easy_setopt(c, CURLOPT_ERRORBUFFER, errbuf);
    curl_easy_setopt(c, CURLOPT_USERAGENT, "el-runtime/1.0");
    if (extra_headers) curl_easy_setopt(c, CURLOPT_HTTPHEADER, extra_headers);
    if (method && strcmp(method, "POST") == 0) {
        curl_easy_setopt(c, CURLOPT_POST, 1L);
        curl_easy_setopt(c, CURLOPT_POSTFIELDS, body ? body : "");
        curl_easy_setopt(c, CURLOPT_POSTFIELDSIZE, (long)(body ? strlen(body) : 0));
    } else if (method && strcmp(method, "DELETE") == 0) {
        curl_easy_setopt(c, CURLOPT_CUSTOMREQUEST, "DELETE");
    }
    CURLcode rc = curl_easy_perform(c);
    curl_easy_cleanup(c);
    if (rc != CURLE_OK) {
        free(rb.data);
        const char* m = errbuf[0] ? errbuf : curl_easy_strerror(rc);
        return http_error_json(m);
    }
    return el_wrap_str(rb.data);
}

el_val_t http_get(el_val_t url) {
    return http_do("GET", EL_CSTR(url), NULL, NULL);
}

el_val_t http_post(el_val_t url, el_val_t body) {
    return http_do("POST", EL_CSTR(url), EL_CSTR(body), NULL);
}

el_val_t http_post_json(el_val_t url, el_val_t json_body) {
    struct curl_slist* h = NULL;
    h = curl_slist_append(h, "Content-Type: application/json");
    el_val_t r = http_do("POST", EL_CSTR(url), EL_CSTR(json_body), h);
    curl_slist_free_all(h);
    return r;
}

/* Build a curl_slist from an ElMap of name -> value strings. */
static struct curl_slist* headers_from_map(el_val_t headers_map) {
    struct curl_slist* h = NULL;
    ElMap* m = as_map(headers_map);
    if (!m) return NULL;
    for (int64_t i = 0; i < m->count; i++) {
        const char* k = EL_CSTR(m->keys[i]);
        const char* v = EL_CSTR(m->values[i]);
        if (!k || !v) continue;
        size_t n = strlen(k) + strlen(v) + 4;
        char* line = malloc(n);
        if (!line) continue;
        snprintf(line, n, "%s: %s", k, v);
        h = curl_slist_append(h, line);
        free(line);
    }
    return h;
}

el_val_t http_get_with_headers(el_val_t url, el_val_t headers_map) {
    struct curl_slist* h = headers_from_map(headers_map);
    el_val_t r = http_do("GET", EL_CSTR(url), NULL, h);
    if (h) curl_slist_free_all(h);
    return r;
}

el_val_t http_post_with_headers(el_val_t url, el_val_t body, el_val_t headers_map) {
    struct curl_slist* h = headers_from_map(headers_map);
    el_val_t r = http_do("POST", EL_CSTR(url), EL_CSTR(body), h);
    if (h) curl_slist_free_all(h);
    return r;
}

/* http_post_json_with_headers — POST with Content-Type: application/json plus
 * any additional headers supplied as an El map.  Combines http_post_json and
 * http_post_with_headers: the Content-Type header is always prepended so
 * callers do not have to include it in their map. */
el_val_t http_post_json_with_headers(el_val_t url, el_val_t headers_map, el_val_t json_body) {
    struct curl_slist* h = NULL;
    h = curl_slist_append(h, "Content-Type: application/json");
    /* Append caller-supplied headers from the map */
    ElMap* m = as_map(headers_map);
    if (m) {
        for (int64_t i = 0; i < m->count; i++) {
            const char* k = EL_CSTR(m->keys[i]);
            const char* v = EL_CSTR(m->values[i]);
            if (!k || !v) continue;
            size_t n = strlen(k) + strlen(v) + 4;
            char* line = malloc(n);
            if (!line) continue;
            snprintf(line, n, "%s: %s", k, v);
            h = curl_slist_append(h, line);
            free(line);
        }
    }
    el_val_t r = http_do("POST", EL_CSTR(url), EL_CSTR(json_body), h);
    curl_slist_free_all(h);
    return r;
}

el_val_t http_post_form_auth(el_val_t url, el_val_t form_body, el_val_t auth_header) {
    struct curl_slist* h = NULL;
    h = curl_slist_append(h, "Content-Type: application/x-www-form-urlencoded");
    const char* a = EL_CSTR(auth_header);
    if (a && *a) {
        size_t n = strlen(a) + 32;
        char* line = malloc(n);
        snprintf(line, n, "Authorization: %s", a);
        h = curl_slist_append(h, line);
        free(line);
    }
    el_val_t r = http_do("POST", EL_CSTR(url), EL_CSTR(form_body), h);
    curl_slist_free_all(h);
    return r;
}

/* HTTP DELETE — mirrors http_post but with CURLOPT_CUSTOMREQUEST=DELETE.
 * Returns response body on success; on transport failure returns an error
 * JSON fragment (same convention as http_get/http_post). Callers that
 * expect "" on failure should check for a leading '{' and an "error" key. */
el_val_t http_delete(el_val_t url) {
    return http_do("DELETE", EL_CSTR(url), NULL, NULL);
}

/* ── HTTP → file streaming ────────────────────────────────────────────────
 *
 * Why this exists: el_val_t strings are NUL-terminated by convention, so
 * accumulating an HTTP response into an httpbuf and then wrapping its
 * `.data` pointer with el_wrap_str() loses the byte length. Any consumer
 * that does strlen() on the wrapped pointer truncates the body at the
 * first embedded NUL. Audio (MP3, WAV, OGG), images (PNG, JPEG), and any
 * other binary payload hits this. The vessels that download such bodies
 * (e.g. ElevenLabs TTS → MP3) get silently corrupted files.
 *
 * The fix: wire libcurl's CURLOPT_WRITEFUNCTION directly to fwrite()
 * against a fopen()-ed FILE*. The bytes never pass through an el_val_t
 * string, so embedded NULs are preserved verbatim. Caller's contract is
 * just "a file at this path with the response body in it". */

static size_t http_file_write_cb(char* ptr, size_t size, size_t nmemb, void* ud) {
    FILE* f = (FILE*)ud;
    return fwrite(ptr, size, nmemb, f);
}

/* Internal: stream body to file. method is "GET" or "POST". body may be NULL
 * (GET) or NUL-terminated (POST). headers may be NULL. Returns 1/0. */
static el_val_t http_do_to_file(const char* method, const char* url,
                                const char* body, struct curl_slist* extra_headers,
                                const char* output_path) {
    if (!url || !*url) return 0;
    if (!output_path || !*output_path) return 0;
    FILE* f = fopen(output_path, "wb");
    if (!f) return 0;

    CURL* c = curl_easy_init();
    if (!c) { fclose(f); remove(output_path); return 0; }

    char errbuf[CURL_ERROR_SIZE]; errbuf[0] = '\0';
    curl_easy_setopt(c, CURLOPT_URL, url);
    curl_easy_setopt(c, CURLOPT_WRITEFUNCTION, http_file_write_cb);
    curl_easy_setopt(c, CURLOPT_WRITEDATA, f);
    curl_easy_setopt(c, CURLOPT_FOLLOWLOCATION, 1L);
    curl_easy_setopt(c, CURLOPT_TIMEOUT_MS, el_http_timeout_ms());
    curl_easy_setopt(c, CURLOPT_NOSIGNAL, 1L);
    curl_easy_setopt(c, CURLOPT_ERRORBUFFER, errbuf);
    curl_easy_setopt(c, CURLOPT_USERAGENT, "el-runtime/1.0");
    curl_easy_setopt(c, CURLOPT_FAILONERROR, 1L);  /* 4xx/5xx → CURLE_HTTP_RETURNED_ERROR */
    if (extra_headers) curl_easy_setopt(c, CURLOPT_HTTPHEADER, extra_headers);

    if (method && strcmp(method, "POST") == 0) {
        curl_easy_setopt(c, CURLOPT_POST, 1L);
        curl_easy_setopt(c, CURLOPT_POSTFIELDS, body ? body : "");
        /* For the request body we still rely on strlen — POST bodies are
         * caller-controlled and JSON/text in every known El use case.
         * If a future caller needs a binary POST body, add a *_bytes
         * variant that takes an explicit length, mirroring fs_write_bytes. */
        curl_easy_setopt(c, CURLOPT_POSTFIELDSIZE, (long)(body ? strlen(body) : 0));
    }

    CURLcode rc = curl_easy_perform(c);
    curl_easy_cleanup(c);

    /* Flush + close before signalling success, so the file is fully on disk
     * by the time the caller reads back. */
    int flush_ok = (fflush(f) == 0);
    int close_ok = (fclose(f) == 0);

    if (rc != CURLE_OK || !flush_ok || !close_ok) {
        remove(output_path);
        return 0;
    }
    return 1;
}

el_val_t http_get_to_file(el_val_t url, el_val_t headers_map, el_val_t output_path) {
    struct curl_slist* h = headers_from_map(headers_map);
    el_val_t r = http_do_to_file("GET", EL_CSTR(url), NULL, h, EL_CSTR(output_path));
    if (h) curl_slist_free_all(h);
    return r;
}

el_val_t http_post_to_file(el_val_t url, el_val_t body, el_val_t headers_map, el_val_t output_path) {
    struct curl_slist* h = headers_from_map(headers_map);
    el_val_t r = http_do_to_file("POST", EL_CSTR(url), EL_CSTR(body), h, EL_CSTR(output_path));
    if (h) curl_slist_free_all(h);
    return r;
}
#endif /* HAVE_CURL */

/* ── HTTP server (POSIX sockets + pthreads) ──────────────────────────────── */

#define HTTP_MAX_CONNS 64

typedef el_val_t (*http_handler_fn)(el_val_t method, el_val_t path, el_val_t body);

typedef struct {
    char*           name;
    http_handler_fn fn;
} HttpHandlerEntry;

static HttpHandlerEntry  _http_handlers[32];
static size_t            _http_handler_count = 0;
static char*             _http_active_handler = NULL;
static pthread_mutex_t   _http_handler_mu = PTHREAD_MUTEX_INITIALIZER;

static pthread_mutex_t   _http_conn_mu = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t    _http_conn_cv = PTHREAD_COND_INITIALIZER;
static int               _http_conn_active = 0;

/* Public C-level API: register a handler by name. Programs that want El
 * `http_serve` to dispatch into their handler call this from main() before
 * http_serve. Not declared in the header to keep the public API minimal —
 * extern lookup works since C symbols are global.                       */
void el_runtime_register_handler(const char* name, http_handler_fn fn);
void el_runtime_register_handler(const char* name, http_handler_fn fn) {
    if (!name || !fn) return;
    pthread_mutex_lock(&_http_handler_mu);
    for (size_t i = 0; i < _http_handler_count; i++) {
        if (strcmp(_http_handlers[i].name, name) == 0) {
            _http_handlers[i].fn = fn;
            pthread_mutex_unlock(&_http_handler_mu);
            return;
        }
    }
    if (_http_handler_count < sizeof(_http_handlers) / sizeof(_http_handlers[0])) {
        _http_handlers[_http_handler_count].name = el_strdup(name);
        _http_handlers[_http_handler_count].fn   = fn;
        _http_handler_count++;
    }
    pthread_mutex_unlock(&_http_handler_mu);
}

el_val_t http_set_handler(el_val_t name) {
    const char* n = EL_CSTR(name);
    pthread_mutex_lock(&_http_handler_mu);
    free(_http_active_handler);
    _http_active_handler = el_strdup(n ? n : "");
    /* If the name is not yet in the registry, try dlsym lookup against
     * the running binary's symbol table. Every El `fn name(...)` compiles
     * to a global C symbol with that exact name, so El programs can self-
     * register their own handlers just by calling http_set_handler("name"). */
    if (n && *n) {
        int found = 0;
        for (size_t i = 0; i < _http_handler_count; i++) {
            if (strcmp(_http_handlers[i].name, n) == 0) { found = 1; break; }
        }
        if (!found) {
            void* sym = dlsym(RTLD_DEFAULT, n);
            if (sym && _http_handler_count < sizeof(_http_handlers) / sizeof(_http_handlers[0])) {
                _http_handlers[_http_handler_count].name = el_strdup(n);
                _http_handlers[_http_handler_count].fn   = (http_handler_fn)sym;
                _http_handler_count++;
            }
        }
    }
    pthread_mutex_unlock(&_http_handler_mu);
    return 0;
}

static http_handler_fn http_lookup_active(void) {
    http_handler_fn out = NULL;
    pthread_mutex_lock(&_http_handler_mu);
    if (_http_active_handler) {
        for (size_t i = 0; i < _http_handler_count; i++) {
            if (strcmp(_http_handlers[i].name, _http_active_handler) == 0) {
                out = _http_handlers[i].fn; break;
            }
        }
    }
    pthread_mutex_unlock(&_http_handler_mu);
    return out;
}

/* Auto-detect Content-Type from response body. */
static const char* http_detect_content_type(const char* body) {
    if (!body) return "text/plain; charset=utf-8";
    const char* p = body;
    /* Binary magic bytes — check before stripping whitespace */
    if ((unsigned char)p[0] == 0x89 && p[1]=='P' && p[2]=='N' && p[3]=='G')
        return "image/png";
    if ((unsigned char)p[0] == 0xFF && (unsigned char)p[1] == 0xD8)
        return "image/jpeg";
    if (strncmp(p, "GIF8", 4) == 0)  return "image/gif";
    if (strncmp(p, "RIFF", 4) == 0)  return "image/webp";
    if (strncmp(p, "wOFF", 4) == 0)  return "font/woff";
    if (strncmp(p, "wOF2", 4) == 0)  return "font/woff2";
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (strncasecmp(p, "<!DOCTYPE", 9) == 0) return "text/html; charset=utf-8";
    if (strncasecmp(p, "<html", 5)    == 0) return "text/html; charset=utf-8";
    if (strncasecmp(p, "<svg",  4)    == 0) return "image/svg+xml";
    if (*p == '{' || *p == '[')             return "application/json; charset=utf-8";
    return "text/plain; charset=utf-8";
}

/* Read the full HTTP request from a connection: request line, headers, body.
 *
 * `out_headers_block` is optional (may be NULL). When non-NULL, on success
 * it receives an allocated NUL-terminated copy of the raw header block —
 * everything between the request line's trailing CRLF and the final \r\n\r\n
 * (no leading/trailing CRLFs). The 3-arg http_serve worker passes NULL here
 * (no headers needed). The 4-arg http_serve_v2 worker passes a real pointer
 * so it can build a header map for the El handler.                         */
static int http_read_request(int fd, char** out_method, char** out_path,
                             char** out_body, char** out_headers_block) {
    *out_method = NULL; *out_path = NULL; *out_body = NULL;
    if (out_headers_block) *out_headers_block = NULL;
    /* Read headers until \r\n\r\n */
    size_t cap = 4096, len = 0;
    char* buf = malloc(cap);
    if (!buf) return -1;
    while (1) {
        if (len + 1 >= cap) {
            if (cap >= 1024 * 1024) { free(buf); return -1; }
            cap *= 2;
            buf = realloc(buf, cap);
            if (!buf) return -1;
        }
        ssize_t n = recv(fd, buf + len, cap - len - 1, 0);
        if (n <= 0) { free(buf); return -1; }
        len += (size_t)n;
        buf[len] = '\0';
        if (strstr(buf, "\r\n\r\n")) break;
    }
    /* Parse request line */
    char* sp1 = strchr(buf, ' ');
    if (!sp1) { free(buf); return -1; }
    *sp1 = '\0';
    *out_method = el_strdup(buf);
    char* path_start = sp1 + 1;
    char* sp2 = strchr(path_start, ' ');
    if (!sp2) { free(*out_method); *out_method = NULL; free(buf); return -1; }
    *sp2 = '\0';
    *out_path = el_strdup(path_start);
    char* hdr_end = strstr(sp2 + 1, "\r\n\r\n");
    /* Capture the raw header block (after the request line's CRLF, up to
     * but not including the terminating \r\n\r\n) for callers that asked
     * for it. The legacy 3-arg path passes NULL and skips this. */
    if (out_headers_block) {
        char* hdr_start = strstr(sp2 + 1, "\r\n");
        if (hdr_start && hdr_start < hdr_end) {
            hdr_start += 2;
            size_t hb_len = (size_t)(hdr_end - hdr_start);
            char* hb = malloc(hb_len + 1);
            if (hb) {
                memcpy(hb, hdr_start, hb_len);
                hb[hb_len] = '\0';
                *out_headers_block = hb;
            }
        } else {
            *out_headers_block = el_strdup("");
        }
    }
    /* Find Content-Length */
    long content_length = 0;
    char* hp = sp2 + 1;
    while (hp < hdr_end) {
        char* line_end = strstr(hp, "\r\n");
        /* line_end == hdr_end means we're on the LAST header line — its
         * trailing \r\n is the same \r\n that begins the \r\n\r\n header
         * terminator. Process this line; only stop when line_end is past
         * hdr_end (which means the parser walked off the end of the
         * header block). The previous condition (line_end >= hdr_end)
         * silently dropped any Content-Length that appeared as the last
         * header — exactly what real curl/clients tend to emit. */
        if (!line_end || line_end > hdr_end) break;
        if (strncasecmp(hp, "Content-Length:", 15) == 0) {
            content_length = strtol(hp + 15, NULL, 10);
            if (content_length < 0) content_length = 0;
            if (content_length > 64 * 1024 * 1024) content_length = 64 * 1024 * 1024;
        }
        hp = line_end + 2;
    }
    /* Body: any bytes already read past hdr_end, plus more recv */
    char* body_start = hdr_end + 4;
    size_t body_have = (buf + len) - body_start;
    char* body = malloc((size_t)content_length + 1);
    if (!body) { free(*out_method); free(*out_path); *out_method=NULL; *out_path=NULL; free(buf); return -1; }
    if ((long)body_have > content_length) body_have = (size_t)content_length;
    if (body_have > 0) memcpy(body, body_start, body_have);
    while ((long)body_have < content_length) {
        ssize_t n = recv(fd, body + body_have, (size_t)content_length - body_have, 0);
        if (n <= 0) break;
        body_have += (size_t)n;
    }
    body[body_have] = '\0';
    *out_body = body;
    free(buf);
    return 0;
}

/* Reason phrase for common HTTP statuses. Falls back to "Status" for the
 * long tail — clients only care about the numeric code. */
static const char* http_reason_phrase(int status) {
    switch (status) {
        case 200: return "OK";
        case 201: return "Created";
        case 202: return "Accepted";
        case 204: return "No Content";
        case 301: return "Moved Permanently";
        case 302: return "Found";
        case 303: return "See Other";
        case 304: return "Not Modified";
        case 307: return "Temporary Redirect";
        case 308: return "Permanent Redirect";
        case 400: return "Bad Request";
        case 401: return "Unauthorized";
        case 403: return "Forbidden";
        case 404: return "Not Found";
        case 405: return "Method Not Allowed";
        case 409: return "Conflict";
        case 410: return "Gone";
        case 422: return "Unprocessable Entity";
        case 429: return "Too Many Requests";
        case 500: return "Internal Server Error";
        case 501: return "Not Implemented";
        case 502: return "Bad Gateway";
        case 503: return "Service Unavailable";
        case 504: return "Gateway Timeout";
        default:  return "Status";
    }
}

/* Best-effort send with retry on partial writes. */
static int http_send_all(int fd, const char* p, size_t left) {
    while (left > 0) {
        ssize_t w = send(fd, p, left, 0);
        if (w <= 0) return -1;
        p += w; left -= (size_t)w;
    }
    return 0;
}

/* Discriminator that http_response() embeds at the start of its envelope.
 * A handler returning a string starting with this exact prefix is treated
 * as a structured response; anything else is treated as a raw body. */
#define EL_HTTP_RESPONSE_TAG "{\"el_http_response\":1"

/* Keys that conflict with runtime-managed headers are silently dropped to
 * avoid double-emission — the runtime always emits its own Content-Length
 * and Connection: close. Content-Type from the envelope IS allowed and
 * overrides auto-detection. */
static int http_header_is_managed(const char* k) {
    return strcasecmp(k, "Content-Length") == 0
        || strcasecmp(k, "Connection") == 0;
}

/* Walk an ElMap of header pairs and emit each as `K: V\r\n` into JsonBuf b.
 * Sets *out_saw_content_type to 1 if the map contained an explicit
 * Content-Type so the caller can skip auto-detection. */
static void http_emit_headers_from_map(JsonBuf* b, el_val_t headers_map,
                                       int* out_saw_content_type) {
    *out_saw_content_type = 0;
    if (headers_map == 0) return;
    ElMap* m = (ElMap*)(uintptr_t)headers_map;
    if (!m || m->hdr.magic != EL_MAGIC_MAP) return;
    for (int64_t i = 0; i < m->count; i++) {
        const char* k = EL_CSTR(m->keys[i]);
        const char* v = EL_CSTR(m->values[i]);
        if (!k || !v) continue;
        if (http_header_is_managed(k)) continue;
        if (strcasecmp(k, "Content-Type") == 0) *out_saw_content_type = 1;
        jb_puts(b, k);
        jb_puts(b, ": ");
        jb_puts(b, v);
        jb_puts(b, "\r\n");
    }
}

/* Parse the envelope produced by http_response(). On success returns 1 and
 * populates *out_status, *out_headers_map (an ElMap el_val_t — caller must
 * el_release via out_parsed_root), and *out_body (malloc'd, caller frees).
 * On failure returns 0.
 *
 * Implementation: manual field scanner — does NOT run json_parse on the full
 * envelope. Running the recursive-descent JSON parser on a 40–50 KB envelope
 * (common when the body contains minified/obfuscated JavaScript) fails because
 * the parser allocates intermediate ElMap nodes for the whole structure.
 * Instead we scan directly:
 *   • "status"  — strtol scan
 *   • "headers" — brace-depth scan to extract the object literal, then
 *                 json_parse only that small substring (always < 1 KB)
 *   • "body"    — jp_parse_string_raw to unescape the JSON string in one pass,
 *                 without building any intermediate data structures           */
static int http_parse_envelope(const char* s, int* out_status,
                               el_val_t* out_headers_map, char** out_body,
                               el_val_t* out_parsed_root) {
    if (!s) return 0;
    if (strncmp(s, EL_HTTP_RESPONSE_TAG,
                sizeof(EL_HTTP_RESPONSE_TAG) - 1) != 0) return 0;

    /* ── status ──────────────────────────────────────────────────────────── */
    int status = 200;
    {
        const char* sp = strstr(s, "\"status\":");
        if (sp) {
            const char* np = sp + 9;
            while (*np == ' ' || *np == '\t') np++;
            long sc = strtol(np, NULL, 10);
            if (sc >= 100 && sc <= 599) status = (int)sc;
        }
    }

    /* ── headers ─────────────────────────────────────────────────────────── */
    el_val_t hmap        = 0;
    el_val_t parsed_hdrs = EL_NULL;
    {
        const char* hp = strstr(s, "\"headers\":");
        if (hp) {
            hp += 10;
            while (*hp == ' ' || *hp == '\t') hp++;
            if (*hp == '{') {
                /* Scan for matching '}', honouring nested objects and strings */
                const char* hobj_start = hp;
                const char* cp = hp + 1;
                int depth = 1, in_str = 0;
                while (*cp && depth > 0) {
                    if (in_str) {
                        if (*cp == '\\' && *(cp + 1)) { cp += 2; continue; }
                        if (*cp == '"') in_str = 0;
                    } else {
                        if      (*cp == '"') in_str = 1;
                        else if (*cp == '{') depth++;
                        else if (*cp == '}') { if (--depth == 0) break; }
                    }
                    cp++;
                }
                if (depth == 0) {
                    /* cp points at the closing '}'; extract the object literal */
                    size_t hlen = (size_t)(cp - hobj_start + 1);
                    char* hobj = malloc(hlen + 1);
                    if (hobj) {
                        memcpy(hobj, hobj_start, hlen);
                        hobj[hlen] = '\0';
                        /* Headers are always simple k/v string pairs — json_parse
                         * is safe on this small substring (typically < 1 KB).   */
                        parsed_hdrs = json_parse(EL_STR(hobj));
                        free(hobj);
                        if (parsed_hdrs != EL_NULL) {
                            ElMap* hm = (ElMap*)(uintptr_t)parsed_hdrs;
                            if (hm && hm->hdr.magic == EL_MAGIC_MAP) hmap = parsed_hdrs;
                        }
                    }
                }
            }
        }
    }

    /* ── body ────────────────────────────────────────────────────────────── */
    /* Search forward so we don't accidentally match "body": inside a header
     * value. http_response() always appends the body field last.            */
    char* body = NULL;
    {
        const char* bp = strstr(s, "\"body\":");
        if (bp) {
            bp += 7;
            while (*bp == ' ' || *bp == '\t') bp++;
            if (*bp == '"') {
                /* jp_parse_string_raw unescapes a JSON string in one pass,
                 * producing a plain malloc'd C string.  Caller frees it.   */
                JsonParser jp = { .p = bp, .end = bp + strlen(bp), .err = 0 };
                char* parsed = jp_parse_string_raw(&jp);
                if (!jp.err) {
                    body = parsed;
                } else {
                    free(parsed);
                }
            }
        }
        if (!body) body = strdup("");
    }

    *out_status      = status;
    *out_headers_map = hmap;
    *out_body        = body;
    *out_parsed_root = parsed_hdrs;  /* caller el_release()s to free hmap */
    return 1;
}

/* Lightweight `__status__` envelope: if the body's first key is `__status__`
 * and its value is a numeric literal, lift the status to the HTTP layer and
 * strip the marker from the body before sending. This is the common case for
 * El handlers that want to return 4xx/5xx without going through
 * http_response() — they just prepend `{"__status__":<int>,...}` to the JSON
 * they were already returning.
 *
 * We deliberately recognise ONLY the first-key form so the contract is cheap
 * to detect and unambiguous: `{"__status__":401,"error":"unauthorized"}` is
 * an envelope, but `{"error":"...","__status__":401}` is not. Product code
 * controls placement.
 *
 * On success returns 1 with *out_status set and *out_body_alloc populated
 * with a freshly malloc'd body (caller frees). On failure returns 0 and
 * leaves outputs untouched. */
static int http_parse_status_envelope(const char* s, int* out_status,
                                      char** out_body_alloc) {
    if (!s) return 0;
    const char* p = s;
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (*p != '{') return 0;
    p++;
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    static const char marker[] = "\"__status__\"";
    size_t mlen = sizeof(marker) - 1;
    if (strncmp(p, marker, mlen) != 0) return 0;
    p += mlen;
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (*p != ':') return 0;
    p++;
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (*p < '0' || *p > '9') return 0;  /* non-numeric -> not an envelope */
    int status = 0;
    while (*p >= '0' && *p <= '9') {
        status = status * 10 + (*p - '0');
        p++;
    }
    if (status < 100 || status > 599) return 0;
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    /* Two trailing shapes accepted:
     *   ,"k":v,...}    -> body becomes {"k":v,...}
     *   }              -> body becomes {}
     * Anything else (e.g. `:` re-appearing, garbage) drops the envelope so
     * we don't strip what we shouldn't. */
    if (*p == '}') {
        *out_status = status;
        *out_body_alloc = el_strdup("{}");
        return 1;
    }
    if (*p != ',') return 0;
    p++;  /* skip the comma; the rest of the object follows */
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    /* Build the trimmed body: '{' + remainder. */
    size_t rest_len = strlen(p);
    char* out = (char*)malloc(rest_len + 2);
    if (!out) return 0;
    out[0] = '{';
    memcpy(out + 1, p, rest_len);
    out[rest_len + 1] = '\0';
    *out_status = status;
    *out_body_alloc = out;
    return 1;
}

/* Send a fully-built HTTP response. If `body` starts with the envelope tag,
 * unpack status/headers/body. Otherwise emit the historical 200-OK with
 * auto-detected Content-Type. */
/* Thread-local flag: if 1, http_send_response writes status + headers but
 * NO body (HEAD method behaviour). Set by http_worker before calling
 * http_send_response, cleared after. */
static __thread int _tl_http_head_only = 0;

static void http_send_response(int fd, const char* body) {
    if (!body) body = "";

    int      status = 200;
    el_val_t env_headers_map = 0;
    char*    env_body = NULL;
    el_val_t env_parsed_root = 0;
    int      is_envelope = http_parse_envelope(body, &status,
                                               &env_headers_map, &env_body,
                                               &env_parsed_root);

    /* If the rich http_response() envelope didn't claim this body, try the
     * lightweight `__status__` form. This second envelope is malloc-backed so
     * we route it through env_body and let the existing cleanup path free it
     * — same lifetime contract, no special case at the bottom of the
     * function. */
    if (!is_envelope) {
        char* trimmed = NULL;
        if (http_parse_status_envelope(body, &status, &trimmed)) {
            env_body = trimmed;
            is_envelope = 1;
        }
    }

    const char* eff_body = is_envelope ? env_body : body;
    int binary_side_channel = 0;

    /* Binary side-channel: if the envelope body is the sentinel "__el_binary__",
     * http_response() stored the real bytes in _tl_binary_body/_tl_binary_size.
     * Substitute them here so http_send_all() sends the correct binary payload. */
    if (is_envelope && env_body && strcmp(env_body, "__el_binary__") == 0
            && _tl_binary_body && _tl_binary_size > 0) {
        eff_body = _tl_binary_body;
        binary_side_channel = 1;
    }

    /* Use the real byte count from fs_read if available (handles binary files
     * with embedded null bytes — PNG, WOFF2, etc.). Fall back to strlen for
     * normal text/JSON responses where _tl_fs_read_len is 0. */
    size_t blen = binary_side_channel ? _tl_binary_size
                : (_tl_fs_read_len > 0) ? _tl_fs_read_len : strlen(eff_body);
    _tl_fs_read_len = 0;  /* consume — one-shot per response */
    int head_only = _tl_http_head_only;

    JsonBuf hdrs; jb_init(&hdrs);
    int saw_content_type = 0;
    if (is_envelope) {
        http_emit_headers_from_map(&hdrs, env_headers_map,
                                   &saw_content_type);
    }
    if (!saw_content_type) {
        jb_puts(&hdrs, "Content-Type: ");
        jb_puts(&hdrs, http_detect_content_type(eff_body));
        jb_puts(&hdrs, "\r\n");
    }

    char status_line[64];
    int sl = snprintf(status_line, sizeof(status_line),
                      "HTTP/1.1 %d %s\r\n",
                      status, http_reason_phrase(status));
    if (sl < 0) {
        if (env_parsed_root) el_release(env_parsed_root);
        free(env_body); free(hdrs.buf); return;
    }

    char tail[128];
    int tl = snprintf(tail, sizeof(tail),
                      "Content-Length: %zu\r\n"
                      "Connection: close\r\n"
                      "\r\n", blen);
    if (tl < 0) {
        if (env_parsed_root) el_release(env_parsed_root);
        free(env_body); free(hdrs.buf); return;
    }

    if (http_send_all(fd, status_line, (size_t)sl) == 0
     && http_send_all(fd, hdrs.buf,    hdrs.len)   == 0
     && http_send_all(fd, tail,        (size_t)tl) == 0
     && (head_only
         /* HEAD requests echo headers + Content-Length but no body. */
         ? 1
         : http_send_all(fd, eff_body, blen) == 0)) {
        /* sent successfully */
    }

    if (env_parsed_root) el_release(env_parsed_root);
    free(env_body);
    free(hdrs.buf);

    /* Release binary side-channel if it was used (or left over from an error). */
    if (_tl_binary_body) {
        free(_tl_binary_body);
        _tl_binary_body = NULL;
        _tl_binary_size = 0;
    }
}

typedef struct {
    int fd;
} HttpWorkerArg;

static void* http_worker(void* arg) {
    HttpWorkerArg* a = (HttpWorkerArg*)arg;
    int fd = a->fd;
    free(a);
    char *method = NULL, *path = NULL, *body = NULL;
    if (http_read_request(fd, &method, &path, &body, NULL) == 0) {
        http_handler_fn h = http_lookup_active();
        char* response = NULL;
        /* HEAD: dispatch as GET so existing handlers respond with the same
         * body, but flag the response writer to emit headers only. RFC 9110
         * requires HEAD to mirror GET headers + Content-Length without body. */
        int head_only = (method && strcmp(method, "HEAD") == 0);
        const char* dispatch_method = head_only ? "GET" : method;
        el_request_start();                         /* begin per-request arena */
        if (h) {
            el_val_t r = h(EL_STR(dispatch_method), EL_STR(path), EL_STR(body));
            const char* rs = EL_CSTR(r);
            /* Copy response out BEFORE arena teardown.
             * For binary files, _tl_fs_read_len holds the real byte count —
             * use memcpy instead of strdup so null bytes are preserved. */
            size_t rlen = _tl_fs_read_len > 0 ? _tl_fs_read_len : (rs ? strlen(rs) : 0);
            response = malloc(rlen + 1);
            if (response && rs) { memcpy(response, rs, rlen); response[rlen] = '\0'; }
            else if (response) { response[0] = '\0'; }
        } else {
            response = el_strdup_persist("el-runtime: no http handler registered");
        }
        el_request_end();                           /* free all intermediate strings */
        _tl_http_head_only = head_only;
        http_send_response(fd, response);
        _tl_http_head_only = 0;
        free(response);
    }
    free(method); free(path); free(body);
    close(fd);
    /* release a slot */
    pthread_mutex_lock(&_http_conn_mu);
    _http_conn_active--;
    pthread_cond_signal(&_http_conn_cv);
    pthread_mutex_unlock(&_http_conn_mu);
    return NULL;
}

el_val_t http_serve(el_val_t port, el_val_t handler) {
    /* If `handler` looks like a string name, register it as the active handler. */
    const char* hname = EL_CSTR(handler);
    if (hname && looks_like_string(handler)) {
        http_set_handler(handler);
    }
    int p = (int)port;
    if (p <= 0 || p > 65535) { fprintf(stderr, "http_serve: invalid port %d\n", p); return 0; }
    /* Dual-stack: AF_INET6 with IPV6_V6ONLY=0 accepts both IPv4 and IPv6.
     * This makes `localhost` work in browsers that resolve it to ::1 first. */
    int sock = socket(AF_INET6, SOCK_STREAM, 0);
    if (sock < 0) { perror("socket"); return 0; }
    int yes = 1; int no = 0;
    setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));
    setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &no, sizeof(no));
    struct sockaddr_in6 addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin6_family = AF_INET6;
    addr.sin6_addr = in6addr_any;
    addr.sin6_port = htons((uint16_t)p);
    if (bind(sock, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
        perror("bind"); close(sock); return 0;
    }
    if (listen(sock, 64) < 0) { perror("listen"); close(sock); return 0; }
    fprintf(stderr, "[http] listening on [::]:%d (dual-stack)\n", p);
    while (1) {
        struct sockaddr_in6 cli;
        socklen_t clen = sizeof(cli);
        int cfd = accept(sock, (struct sockaddr*)&cli, &clen);
        if (cfd < 0) {
            if (errno == EINTR) continue;
            perror("accept"); break;
        }
        pthread_mutex_lock(&_http_conn_mu);
        while (_http_conn_active >= HTTP_MAX_CONNS) {
            pthread_cond_wait(&_http_conn_cv, &_http_conn_mu);
        }
        _http_conn_active++;
        pthread_mutex_unlock(&_http_conn_mu);
        HttpWorkerArg* arg = malloc(sizeof(HttpWorkerArg));
        if (!arg) { close(cfd); continue; }
        arg->fd = cfd;
        pthread_t tid;
        if (pthread_create(&tid, NULL, http_worker, arg) != 0) {
            close(cfd); free(arg);
            pthread_mutex_lock(&_http_conn_mu);
            _http_conn_active--;
            pthread_cond_signal(&_http_conn_cv);
            pthread_mutex_unlock(&_http_conn_mu);
            continue;
        }
        pthread_detach(tid);
    }
    close(sock);
    return 0;
}

/* ── HTTP server v2 — request headers + structured response ──────────────── */
/*
 * v2 widens the handler signature from
 *     (method, path, body) -> body_string
 * to
 *     (method, path, headers_map, body) -> body_string_or_envelope
 *
 * The response envelope is detected uniformly inside http_send_response — so
 * 4-arg handlers can return either a plain body or http_response(...). The
 * 3-arg path stays untouched in spirit (its handlers still build plain
 * bodies; the envelope tag, being `{"el_http_response":1`, will never
 * collide with normal JSON the legacy server.el routes return).
 *
 * Registry is parallel to the 3-arg handler registry: separate name table,
 * separate active-handler slot, separate dlsym fallback. Mixing v1 and v2
 * handlers in the same process is fine — they don't share the active slot. */

typedef el_val_t (*http_handler4_fn)(el_val_t method, el_val_t path,
                                     el_val_t headers_map, el_val_t body);

typedef struct {
    char*             name;
    http_handler4_fn  fn;
} HttpHandler4Entry;

static HttpHandler4Entry _http_handlers4[32];
static size_t            _http_handler4_count = 0;
static char*             _http_active_handler4 = NULL;

void el_runtime_register_handler_v2(const char* name, http_handler4_fn fn);
void el_runtime_register_handler_v2(const char* name, http_handler4_fn fn) {
    if (!name || !fn) return;
    pthread_mutex_lock(&_http_handler_mu);
    for (size_t i = 0; i < _http_handler4_count; i++) {
        if (strcmp(_http_handlers4[i].name, name) == 0) {
            _http_handlers4[i].fn = fn;
            pthread_mutex_unlock(&_http_handler_mu);
            return;
        }
    }
    if (_http_handler4_count <
        sizeof(_http_handlers4) / sizeof(_http_handlers4[0])) {
        _http_handlers4[_http_handler4_count].name = el_strdup(name);
        _http_handlers4[_http_handler4_count].fn   = fn;
        _http_handler4_count++;
    }
    pthread_mutex_unlock(&_http_handler_mu);
}

el_val_t http_set_handler_v2(el_val_t name) {
    const char* n = EL_CSTR(name);
    pthread_mutex_lock(&_http_handler_mu);
    free(_http_active_handler4);
    _http_active_handler4 = el_strdup(n ? n : "");
    if (n && *n) {
        int found = 0;
        for (size_t i = 0; i < _http_handler4_count; i++) {
            if (strcmp(_http_handlers4[i].name, n) == 0) { found = 1; break; }
        }
        if (!found) {
            void* sym = dlsym(RTLD_DEFAULT, n);
            if (sym && _http_handler4_count <
                sizeof(_http_handlers4) / sizeof(_http_handlers4[0])) {
                _http_handlers4[_http_handler4_count].name = el_strdup(n);
                _http_handlers4[_http_handler4_count].fn   =
                    (http_handler4_fn)sym;
                _http_handler4_count++;
            }
        }
    }
    pthread_mutex_unlock(&_http_handler_mu);
    return 0;
}

static http_handler4_fn http_lookup_active_v2(void) {
    http_handler4_fn out = NULL;
    pthread_mutex_lock(&_http_handler_mu);
    if (_http_active_handler4) {
        for (size_t i = 0; i < _http_handler4_count; i++) {
            if (strcmp(_http_handlers4[i].name,
                       _http_active_handler4) == 0) {
                out = _http_handlers4[i].fn; break;
            }
        }
    }
    pthread_mutex_unlock(&_http_handler_mu);
    return out;
}

/* Build an ElMap from the raw header block produced by http_read_request.
 * Keys are lowercased (RFC 7230 — case-insensitive); values have leading
 * whitespace trimmed. Repeated headers with the same name are joined with
 * ", " in arrival order, matching standard library behaviour elsewhere. */
static el_val_t http_build_headers_map(const char* hdr_block) {
    el_val_t m = el_map_new(0);
    if (!hdr_block || !*hdr_block) return m;
    const char* p = hdr_block;
    while (*p) {
        const char* line_end = strstr(p, "\r\n");
        const char* end = line_end ? line_end : p + strlen(p);
        const char* colon = NULL;
        for (const char* c = p; c < end; c++) {
            if (*c == ':') { colon = c; break; }
        }
        if (colon && colon > p) {
            size_t klen = (size_t)(colon - p);
            char* key = malloc(klen + 1);
            if (key) {
                for (size_t i = 0; i < klen; i++) {
                    unsigned char ch = (unsigned char)p[i];
                    key[i] = (char)tolower(ch);
                }
                key[klen] = '\0';
                const char* vstart = colon + 1;
                while (vstart < end && (*vstart == ' ' || *vstart == '\t')) vstart++;
                size_t vlen = (size_t)(end - vstart);
                /* Strip trailing OWS just in case. */
                while (vlen > 0
                       && (vstart[vlen - 1] == ' '
                        || vstart[vlen - 1] == '\t')) vlen--;
                /* Coalesce repeats: if key already present, append ", value". */
                el_val_t existing = el_map_get(m, EL_STR(key));
                if (existing != 0 && looks_like_string(existing)) {
                    const char* old = EL_CSTR(existing);
                    size_t olen = strlen(old);
                    char* combined = malloc(olen + 2 + vlen + 1);
                    if (combined) {
                        memcpy(combined, old, olen);
                        memcpy(combined + olen, ", ", 2);
                        memcpy(combined + olen + 2, vstart, vlen);
                        combined[olen + 2 + vlen] = '\0';
                        m = el_map_set(m, EL_STR(key), EL_STR(combined));
                    }
                    free(key);
                } else {
                    char* val = malloc(vlen + 1);
                    if (val) {
                        memcpy(val, vstart, vlen);
                        val[vlen] = '\0';
                        m = el_map_set(m, EL_STR(key), EL_STR(val));
                    } else {
                        free(key);
                    }
                }
            }
        }
        if (!line_end) break;
        p = line_end + 2;
    }
    return m;
}

static void* http_worker_v2(void* arg) {
    HttpWorkerArg* a = (HttpWorkerArg*)arg;
    int fd = a->fd;
    free(a);
    char *method = NULL, *path = NULL, *body = NULL, *hdr_block = NULL;
    if (http_read_request(fd, &method, &path, &body, &hdr_block) == 0) {
        http_handler4_fn h = http_lookup_active_v2();
        char* response = NULL;
        int head_only = (method && strcmp(method, "HEAD") == 0);
        const char* dispatch_method = head_only ? "GET" : method;
        el_request_start();                         /* begin per-request arena */
        if (h) {
            el_val_t hmap = http_build_headers_map(hdr_block ? hdr_block : "");
            el_val_t r = h(EL_STR(dispatch_method), EL_STR(path), hmap, EL_STR(body));
            const char* rs = EL_CSTR(r);
            size_t rlen = _tl_fs_read_len > 0 ? _tl_fs_read_len : (rs ? strlen(rs) : 0);
            response = malloc(rlen + 1);
            if (response && rs) { memcpy(response, rs, rlen); response[rlen] = '\0'; }
            else if (response) { response[0] = '\0'; }
            el_release(hmap);
        } else {
            response = el_strdup_persist(
                "el-runtime: no v2 http handler registered "
                "(call http_set_handler_v2)");
        }
        el_request_end();                           /* free all intermediate strings */
        _tl_http_head_only = head_only;
        http_send_response(fd, response);
        _tl_http_head_only = 0;
        free(response);
    }
    free(method); free(path); free(body); free(hdr_block);
    close(fd);
    pthread_mutex_lock(&_http_conn_mu);
    _http_conn_active--;
    pthread_cond_signal(&_http_conn_cv);
    pthread_mutex_unlock(&_http_conn_mu);
    return NULL;
}

el_val_t http_serve_v2(el_val_t port, el_val_t handler) {
    const char* hname = EL_CSTR(handler);
    if (hname && looks_like_string(handler)) {
        http_set_handler_v2(handler);
    }
    int p = (int)port;
    if (p <= 0 || p > 65535) {
        fprintf(stderr, "http_serve_v2: invalid port %d\n", p);
        return 0;
    }
    /* Dual-stack: same as http_serve - AF_INET6 + IPV6_V6ONLY=0. */
    int sock = socket(AF_INET6, SOCK_STREAM, 0);
    if (sock < 0) { perror("socket"); return 0; }
    int yes = 1; int no = 0;
    setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes));
    setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &no, sizeof(no));
    struct sockaddr_in6 addr;
    memset(&addr, 0, sizeof(addr));
    addr.sin6_family = AF_INET6;
    addr.sin6_addr = in6addr_any;
    addr.sin6_port = htons((uint16_t)p);
    if (bind(sock, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
        perror("bind"); close(sock); return 0;
    }
    if (listen(sock, 64) < 0) { perror("listen"); close(sock); return 0; }
    fprintf(stderr, "[http v2] listening on [::]:%d (dual-stack)\n", p);
    while (1) {
        struct sockaddr_in6 cli;
        socklen_t clen = sizeof(cli);
        int cfd = accept(sock, (struct sockaddr*)&cli, &clen);
        if (cfd < 0) {
            if (errno == EINTR) continue;
            perror("accept"); break;
        }
        pthread_mutex_lock(&_http_conn_mu);
        while (_http_conn_active >= HTTP_MAX_CONNS) {
            pthread_cond_wait(&_http_conn_cv, &_http_conn_mu);
        }
        _http_conn_active++;
        pthread_mutex_unlock(&_http_conn_mu);
        HttpWorkerArg* arg = malloc(sizeof(HttpWorkerArg));
        if (!arg) { close(cfd); continue; }
        arg->fd = cfd;
        pthread_t tid;
        if (pthread_create(&tid, NULL, http_worker_v2, arg) != 0) {
            close(cfd); free(arg);
            pthread_mutex_lock(&_http_conn_mu);
            _http_conn_active--;
            pthread_cond_signal(&_http_conn_cv);
            pthread_mutex_unlock(&_http_conn_mu);
            continue;
        }
        pthread_detach(tid);
    }
    close(sock);
    return 0;
}

/* Build the response envelope a 4-arg handler can return. We hand-write
 * the JSON so the discriminator key always lands first — the runtime's
 * http_parse_envelope() detects it via prefix match. headers_json must be
 * either "" (empty), "{}" (empty object), or a well-formed JSON object
 * literal; anything else will produce a malformed envelope and the runtime
 * will treat the whole string as a plain body (no envelope detected).   */
el_val_t http_response(el_val_t status, el_val_t headers_json, el_val_t body) {
    long sc = (long)status;
    if (sc < 100 || sc > 599) sc = 200;
    const char* hj = EL_CSTR(headers_json);
    if (!hj || !*hj) hj = "{}";
    /* Light validation: must start with '{' and end with '}'. */
    size_t hlen = strlen(hj);
    int hj_ok = (hlen >= 2 && hj[0] == '{' && hj[hlen - 1] == '}');
    if (!hj_ok) hj = "{}";
    const char* b = EL_CSTR(body);
    if (!b) b = "";

    /* Capture binary length BEFORE clearing _tl_fs_read_len.
     * If the body came from fs_read(), _tl_fs_read_len holds the real byte
     * count. jb_emit_escaped() stops at the first NUL byte, so we cannot
     * JSON-encode binary data directly. Instead we copy it to a thread-local
     * side-channel and write the sentinel "__el_binary__" into the envelope.
     * http_send_response() detects the sentinel and uses the side-channel. */
    size_t binary_len = _tl_fs_read_len;

    /* Clear the fs_read binary-length hint: the envelope we're about to build
     * is a fresh JSON string, not the raw file bytes.  Without this reset,
     * http_worker would use the stale _tl_fs_read_len (= original file size)
     * to copy the response — truncating the larger envelope before it reaches
     * http_send_response and http_parse_envelope.                            */
    _tl_fs_read_len = 0;

    if (binary_len > 0) {
        /* Binary body path: store raw bytes in thread-local, emit sentinel. */
        free(_tl_binary_body);        /* discard any stale binary from a prior error path */
        _tl_binary_body = malloc(binary_len);
        if (_tl_binary_body) {
            memcpy(_tl_binary_body, b, binary_len);
            _tl_binary_size = binary_len;
        } else {
            _tl_binary_size = 0;      /* malloc failed — fall through to empty body */
        }
    }

    JsonBuf out; jb_init(&out);
    jb_puts(&out, EL_HTTP_RESPONSE_TAG);  /* {"el_http_response":1 */
    jb_puts(&out, ",\"status\":");
    char num[32];
    snprintf(num, sizeof(num), "%ld", sc);
    jb_puts(&out, num);
    jb_puts(&out, ",\"headers\":");
    jb_puts(&out, hj);
    jb_puts(&out, ",\"body\":");
    if (binary_len > 0 && _tl_binary_body) {
        /* Sentinel: http_send_response() will substitute the real bytes. */
        jb_puts(&out, "\"__el_binary__\"");
    } else {
        jb_emit_escaped(&out, b);
    }
    jb_putc(&out, '}');
    return el_wrap_str(out.buf);
}

/* ── Filesystem ──────────────────────────────────────────────────────────── */

el_val_t fs_read(el_val_t pathv) {
    const char* path = EL_CSTR(pathv);
    _tl_fs_read_len = 0;
    if (!path) return el_wrap_str(el_strdup(""));
    FILE* f = fopen(path, "rb");
    if (!f) return el_wrap_str(el_strdup(""));
    fseek(f, 0, SEEK_END);
    long sz = ftell(f);
    rewind(f);
    if (sz < 0) { fclose(f); return el_wrap_str(el_strdup("")); } /* pipe/special file */
    char* buf = el_strbuf((size_t)sz);
    size_t got = fread(buf, 1, (size_t)sz, f);
    buf[got] = '\0';
    _tl_fs_read_len = got;   /* store real byte count for binary-safe send */
    fclose(f);
    return el_wrap_str(buf);
}

el_val_t fs_write(el_val_t pathv, el_val_t contentv) {
    const char* path    = EL_CSTR(pathv);
    const char* content = EL_CSTR(contentv);
    if (!path || !content) return 0;
    FILE* f = fopen(path, "wb");
    if (!f) return 0;
    size_t n       = strlen(content);
    size_t written = fwrite(content, 1, n, f);
    fclose(f);
    return written == n ? 1 : 0;
}

/* fs_write_bytes — explicit-length binary write. Bypasses strlen so embedded
 * NULs survive. Caller must know the byte count (e.g. from base64_decode,
 * or the fixed 32-byte sha256_bytes/hmac_sha256_bytes outputs).
 *
 * If `length` is negative, treats as failure. If `length` is 0, creates an
 * empty file (still useful as a "touch with content" primitive). */
el_val_t fs_write_bytes(el_val_t pathv, el_val_t bytesv, el_val_t lengthv) {
    const char* path  = EL_CSTR(pathv);
    const char* bytes = EL_CSTR(bytesv);
    int64_t     n     = (int64_t)lengthv;
    if (!path || !bytes) return 0;
    if (n < 0) return 0;
    FILE* f = fopen(path, "wb");
    if (!f) return 0;
    size_t written = (n > 0) ? fwrite(bytes, 1, (size_t)n, f) : 0;
    int flush_ok = (fflush(f) == 0);
    int close_ok = (fclose(f) == 0);
    if (!flush_ok || !close_ok || written != (size_t)n) {
        remove(path);
        return 0;
    }
    return 1;
}

// stdout_to_file / stdout_restore — redirect process stdout to a file and
// restore it. Used by the compiler's JS post-processing pipeline to capture
// codegen output before piping through terser / obfuscator.
#include <fcntl.h>
static int _el_saved_stdout_fd = -1;

el_val_t stdout_to_file(el_val_t pathv) {
    const char* path = EL_CSTR(pathv);
    if (!path) return (el_val_t)(int64_t)-1;
    fflush(stdout);
    _el_saved_stdout_fd = dup(STDOUT_FILENO);
    int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0600);
    if (fd < 0) return (el_val_t)(int64_t)-1;
    dup2(fd, STDOUT_FILENO);
    close(fd);
    return (el_val_t)(int64_t)0;
}

el_val_t stdout_restore(void) {
    if (_el_saved_stdout_fd >= 0) {
        fflush(stdout);
        dup2(_el_saved_stdout_fd, STDOUT_FILENO);
        close(_el_saved_stdout_fd);
        _el_saved_stdout_fd = -1;
    }
    return (el_val_t)(int64_t)0;
}

// exec_command — run a shell command, return exit code (0 = success).
// Used by elb and other El tooling to invoke subprocesses.
el_val_t exec_command(el_val_t cmdv) {
    const char* cmd = EL_CSTR(cmdv);
    if (!cmd) return (el_val_t)(int64_t)-1;
    int ret = system(cmd);
    return (el_val_t)(int64_t)ret;
}

// exec_capture — run a shell command, capture stdout, return as String.
// Returns "" on failure.
el_val_t exec_capture(el_val_t cmdv) {
    const char* cmd = EL_CSTR(cmdv);
    if (!cmd) return el_wrap_str(el_strdup(""));
    FILE* f = popen(cmd, "r");
    if (!f) return el_wrap_str(el_strdup(""));
    JsonBuf b; jb_init(&b);
    char buf[4096];
    while (fgets(buf, sizeof(buf), f)) jb_puts(&b, buf);
    pclose(f);
    return el_wrap_str(b.buf);
}

// exec — run a shell command via /bin/sh, capture stdout, return as String.
// Times out after 30 seconds. Returns "" on any error.
// El name: exec(cmd) -> String
el_val_t exec(el_val_t cmdv) {
    const char* cmd = EL_CSTR(cmdv);
    if (!cmd || !*cmd) return el_wrap_str(el_strdup(""));
    /* Build a time-limited command: wrap with timeout(1) if available,
     * otherwise rely on the 30s read loop guard below. We use the simple
     * popen approach with a deadline measured by wall clock so the caller
     * is never blocked indefinitely. */
    FILE* f = popen(cmd, "r");
    if (!f) return el_wrap_str(el_strdup(""));
    JsonBuf b; jb_init(&b);
    char buf[4096];
    /* 30-second wall-clock deadline */
    time_t deadline = time(NULL) + 30;
    while (time(NULL) < deadline) {
        if (fgets(buf, sizeof(buf), f) == NULL) break;
        jb_puts(&b, buf);
    }
    pclose(f);
    return el_wrap_str(b.buf);
}

// exec_bg — run a shell command in background, return PID as String.
// The child process runs independently; the caller is not blocked.
// Returns "" on fork failure.
// El name: exec_bg(cmd) -> String
el_val_t exec_bg(el_val_t cmdv) {
    const char* cmd = EL_CSTR(cmdv);
    if (!cmd || !*cmd) return el_wrap_str(el_strdup(""));
    pid_t pid = fork();
    if (pid < 0) {
        /* fork failed */
        return el_wrap_str(el_strdup(""));
    }
    if (pid == 0) {
        /* child: detach from parent's stdio, exec via shell */
        setsid();
        int devnull = open("/dev/null", O_RDWR);
        if (devnull >= 0) {
            dup2(devnull, STDIN_FILENO);
            dup2(devnull, STDOUT_FILENO);
            dup2(devnull, STDERR_FILENO);
            close(devnull);
        }
        execl("/bin/sh", "sh", "-c", cmd, (char*)NULL);
        _exit(127);
    }
    /* parent: convert pid to string and return immediately */
    char pidbuf[32];
    snprintf(pidbuf, sizeof(pidbuf), "%d", (int)pid);
    return el_wrap_str(el_strdup(pidbuf));
}

el_val_t fs_list(el_val_t pathv) {
    const char* path = EL_CSTR(pathv);
    el_val_t lst = el_list_empty();
    if (!path) return lst;
    DIR* d = opendir(path);
    if (!d) return lst;
    struct dirent* e;
    while ((e = readdir(d)) != NULL) {
        if (strcmp(e->d_name, ".") == 0 || strcmp(e->d_name, "..") == 0) continue;
        lst = el_list_append(lst, el_wrap_str(el_strdup(e->d_name)));
    }
    closedir(d);
    return lst;
}

/* fs_list_json — return directory entries as a JSON array of strings.
 * Returns "[]" for missing or non-directory paths. Excludes "." and "..". */
el_val_t fs_list_json(el_val_t pathv) {
    const char* path = EL_CSTR(pathv);
    if (!path) return EL_STR("[]");
    DIR* d = opendir(path);
    if (!d) return EL_STR("[]");
    /* Collect entries first so we can build the JSON in one pass. */
    char** names = NULL;
    size_t count = 0, cap = 0;
    struct dirent* e;
    while ((e = readdir(d)) != NULL) {
        if (strcmp(e->d_name, ".") == 0 || strcmp(e->d_name, "..") == 0) continue;
        if (count >= cap) {
            cap = cap ? cap * 2 : 16;
            names = realloc(names, cap * sizeof(char*));
            if (!names) { closedir(d); return EL_STR("[]"); }
        }
        names[count++] = strdup(e->d_name);
    }
    closedir(d);
    /* Build JSON array. */
    size_t sz = 3; /* "[]" + NUL */
    for (size_t i = 0; i < count; i++) sz += strlen(names[i]) * 2 + 6; /* conservative */
    char* buf = malloc(sz);
    if (!buf) { for (size_t i = 0; i < count; i++) free(names[i]); free(names); return EL_STR("[]"); }
    size_t pos = 0;
    buf[pos++] = '[';
    for (size_t i = 0; i < count; i++) {
        if (i > 0) buf[pos++] = ',';
        buf[pos++] = '"';
        for (const char* p = names[i]; *p; p++) {
            if (*p == '"' || *p == '\\') buf[pos++] = '\\';
            else if (*p == '\n') { buf[pos++] = '\\'; buf[pos++] = 'n'; continue; }
            else if (*p == '\t') { buf[pos++] = '\\'; buf[pos++] = 't'; continue; }
            buf[pos++] = *p;
        }
        buf[pos++] = '"';
        free(names[i]);
    }
    free(names);
    buf[pos++] = ']';
    buf[pos] = '\0';
    return el_wrap_str(buf);
}

/* fs_exists — true iff stat(path) succeeds. Symlinks are followed. */
el_val_t fs_exists(el_val_t pathv) {
    const char* path = EL_CSTR(pathv);
    if (!path || !*path) return 0;
    struct stat st;
    return (el_val_t)(stat(path, &st) == 0 ? 1 : 0);
}

/* fs_mkdir — create directory at path with mode 0755, mkdir -p semantics.
 * Returns 1 if path exists or was created (incl. all parents); 0 on failure.
 * Walks the path component-by-component so missing intermediate dirs are
 * also created. An existing leaf is not an error. */
el_val_t fs_mkdir(el_val_t pathv) {
    const char* path = EL_CSTR(pathv);
    if (!path || !*path) return 0;
    size_t n = strlen(path);
    char* buf = malloc(n + 1);
    if (!buf) return 0;
    memcpy(buf, path, n + 1);
    /* Walk components; create each prefix in turn. */
    for (size_t i = 1; i <= n; i++) {
        if (buf[i] == '/' || buf[i] == '\0') {
            char saved = buf[i];
            buf[i] = '\0';
            if (buf[0] != '\0') {
                if (mkdir(buf, 0755) != 0 && errno != EEXIST) {
                    /* Tolerate the case where this prefix exists as a non-dir
                     * only when stat says it's a directory. */
                    struct stat st;
                    if (stat(buf, &st) != 0 || !S_ISDIR(st.st_mode)) {
                        free(buf);
                        return 0;
                    }
                }
            }
            buf[i] = saved;
        }
    }
    free(buf);
    return 1;
}

/* ── URL encoding ─────────────────────────────────────────────────────────── */

/* RFC 3986 percent-encoding for URL components (form bodies, query strings).
 * Unreserved set: A-Z a-z 0-9 - _ . ~ — passed through verbatim.
 * Everything else (including space) becomes %XX hex. */
el_val_t url_encode(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return el_wrap_str(el_strdup(""));
    static const char hex[] = "0123456789ABCDEF";
    size_t n = strlen(s);
    char* out = el_strbuf(n * 3);
    size_t o = 0;
    for (size_t i = 0; i < n; i++) {
        unsigned char c = (unsigned char)s[i];
        if ((c >= 'A' && c <= 'Z') ||
            (c >= 'a' && c <= 'z') ||
            (c >= '0' && c <= '9') ||
            c == '-' || c == '_' || c == '.' || c == '~') {
            out[o++] = (char)c;
        } else {
            out[o++] = '%';
            out[o++] = hex[(c >> 4) & 0xF];
            out[o++] = hex[c & 0xF];
        }
    }
    out[o] = '\0';
    return el_wrap_str(out);
}

/* Decode percent-encoded URL component. '+' becomes space (form-encoded);
 * malformed %-escapes are emitted verbatim. */
el_val_t url_decode(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return el_wrap_str(el_strdup(""));
    size_t n = strlen(s);
    char* out = el_strbuf(n);
    size_t o = 0;
    for (size_t i = 0; i < n; i++) {
        char c = s[i];
        if (c == '+') {
            out[o++] = ' ';
        } else if (c == '%' && i + 2 < n) {
            char h1 = s[i + 1], h2 = s[i + 2];
            int v1 = (h1 >= '0' && h1 <= '9') ? h1 - '0'
                   : (h1 >= 'a' && h1 <= 'f') ? h1 - 'a' + 10
                   : (h1 >= 'A' && h1 <= 'F') ? h1 - 'A' + 10 : -1;
            int v2 = (h2 >= '0' && h2 <= '9') ? h2 - '0'
                   : (h2 >= 'a' && h2 <= 'f') ? h2 - 'a' + 10
                   : (h2 >= 'A' && h2 <= 'F') ? h2 - 'A' + 10 : -1;
            if (v1 >= 0 && v2 >= 0) {
                out[o++] = (char)((v1 << 4) | v2);
                i += 2;
            } else {
                out[o++] = c;
            }
        } else {
            out[o++] = c;
        }
    }
    out[o] = '\0';
    return el_wrap_str(out);
}

/* ── html_raw ────────────────────────────────────────────────────────────────
 * Identity passthrough for raw HTML template interpolation.
 * El's {raw(expr)} compiles to html_raw(expr) — the value is output as-is
 * without any escaping. The caller is responsible for safety.
 */
el_val_t html_raw(el_val_t s) {
    return s;
}

/* ── html_escape ─────────────────────────────────────────────────────────────
 * Escape < > " ' & for safe HTML text interpolation.
 * El's {expr} in HTML templates compiles to html_escape(expr).
 */
el_val_t html_escape(el_val_t sv) {
    const char* src = EL_CSTR(sv);
    if (!src) return EL_STR("");
    size_t len = strlen(src);
    /* Worst case: every byte → 6 chars (&quot;) */
    char* out = (char*)malloc(len * 6 + 1);
    if (!out) return sv;
    el_arena_track(out);
    char* p = out;
    for (size_t i = 0; i < len; i++) {
        unsigned char c = (unsigned char)src[i];
        switch (c) {
            case '&':  memcpy(p, "&amp;",  5); p += 5; break;
            case '<':  memcpy(p, "&lt;",   4); p += 4; break;
            case '>':  memcpy(p, "&gt;",   4); p += 4; break;
            case '"':  memcpy(p, "&quot;", 6); p += 6; break;
            case '\'': memcpy(p, "&#39;",  5); p += 5; break;
            default:   *p++ = (char)c;          break;
        }
    }
    *p = '\0';
    return el_wrap_str(out);
}

/* ── HTML allowlist sanitizer ────────────────────────────────────────────────
 * el_html_sanitize(input, allowlist_json)
 *
 * Strict allowlist HTML cleaner. Replaces the older denylist patterns
 * (str_replace cascades that wrapped dangerous tags in HTML comments and
 * renamed `on*` attributes). The denylist approach is fragile: comment-
 * wrapping can be re-broken by a literal `-->` inside an attacker-supplied
 * attribute value, and every new attack vector requires a code change.
 *
 * Design:
 *   - Single-pass byte-level state machine.
 *   - Tag and attribute names are matched case-insensitively against the
 *     allowlist. Unknown tags are dropped entirely (the open and close
 *     markers are stripped; their inner text content survives, escaped).
 *   - A small set of "dangerous container" tags (script, style, iframe,
 *     object, embed, form, plus a few rarer ones) drop themselves AND
 *     their full subtree — text between `<script>` and `</script>` is
 *     CDATA-like and must not be re-emitted as escaped text either.
 *   - Comments (<!-- -->), doctype (<!DOCTYPE>), CDATA (<![CDATA[...]]>),
 *     and processing instructions (<?...?>) are dropped entirely.
 *   - Text content outside dropped subtrees is HTML-escaped (&, <, >, ", ').
 *   - Attribute values are unquoted/dequoted, then re-emitted with double
 *     quotes around the cleanly-escaped value.
 *   - For `<a href>` and any `src` attribute, the URL scheme is validated:
 *     only http:, https:, mailto:, fragment-only `#anchor`, or relative
 *     paths are allowed. Anything else (javascript:, data:, vbscript:,
 *     about:, file:, etc.) drops the attribute.
 *   - Self-closing void tags (br, hr, img, etc.) emit without a close tag.
 *   - Malformed input (unclosed tag at EOF, bad attribute syntax) drops
 *     the pending tag and continues. Pre-encoded entities (&lt;, &amp;,
 *     etc.) are passed through verbatim — the browser will decode them
 *     safely on render.
 *
 * Allowlist format (JSON string):
 *   {"p":[],"a":["href","title"],"strong":[],...}
 *   - Key = lowercase tag name.
 *   - Value = JSON array of allowed attribute names (lowercase).
 *   - Empty array means tag allowed but no attributes survive.
 *
 * Output is a freshly-allocated arena-tracked el_val_t string. */

/* Internal byte buffer with realloc-doubling. Used during sanitization;
 * the final result is copied into an arena-tracked el_strbuf so the caller
 * sees standard runtime memory semantics. */
typedef struct {
    char*  data;
    size_t len;
    size_t cap;
} html_buf_t;

static void html_buf_init(html_buf_t* b) {
    b->cap = 256;
    b->data = malloc(b->cap);
    if (!b->data) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    b->len = 0;
}

static void html_buf_grow(html_buf_t* b, size_t need) {
    if (b->len + need + 1 <= b->cap) return;
    size_t nc = b->cap;
    while (b->len + need + 1 > nc) nc *= 2;
    char* nd = realloc(b->data, nc);
    if (!nd) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    b->data = nd;
    b->cap = nc;
}

static void html_buf_putc(html_buf_t* b, char c) {
    html_buf_grow(b, 1);
    b->data[b->len++] = c;
}

static void html_buf_puts(html_buf_t* b, const char* s) {
    if (!s) return;
    size_t n = strlen(s);
    html_buf_grow(b, n);
    memcpy(b->data + b->len, s, n);
    b->len += n;
}

static void html_buf_free(html_buf_t* b) {
    free(b->data);
    b->data = NULL;
    b->len = b->cap = 0;
}

/* ASCII tolower, locale-independent. */
static int html_tolower(int c) {
    return (c >= 'A' && c <= 'Z') ? c + 32 : c;
}

/* Case-insensitive ASCII compare of [a, a+n) against c-string `s`.
 * Returns 1 iff lengths match and bytes are equal under tolower. */
static int html_ieq_n(const char* a, size_t n, const char* s) {
    if (!a || !s) return 0;
    if (strlen(s) != n) return 0;
    for (size_t i = 0; i < n; i++) {
        if (html_tolower((unsigned char)a[i]) != html_tolower((unsigned char)s[i])) return 0;
    }
    return 1;
}

/* Case-insensitive ASCII compare of two byte slices. */
static int html_iemem(const char* a, const char* b, size_t n) {
    for (size_t i = 0; i < n; i++) {
        if (html_tolower((unsigned char)a[i]) != html_tolower((unsigned char)b[i])) return 0;
    }
    return 1;
}

/* Walk a JSON allowlist object and find the value (an array) for a given
 * tag key, comparing case-insensitively. On hit returns a pointer to the
 * opening `[` of the array and writes the byte length of the array span
 * (including the brackets) to *out_len. On miss returns NULL.
 *
 * The parser is intentionally tiny: it does not handle escapes inside
 * keys (allowlist authors do not need them), and it relies on balanced
 * brackets/quotes within the value array. */
static const char* html_allowlist_find(const char* allow, const char* tag,
                                       size_t tag_len, size_t* out_len) {
    if (!allow) return NULL;
    const char* p = allow;
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (*p != '{') return NULL;
    p++;
    while (*p) {
        while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r' || *p == ',') p++;
        if (*p == '}' || *p == 0) return NULL;
        if (*p != '"') return NULL;
        p++;
        const char* k = p;
        while (*p && *p != '"') p++;
        if (*p != '"') return NULL;
        size_t klen = (size_t)(p - k);
        p++;
        while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
        if (*p != ':') return NULL;
        p++;
        while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
        if (*p != '[') return NULL;
        const char* arr_start = p;
        int depth = 0;
        int in_str = 0;
        while (*p) {
            char c = *p;
            if (in_str) {
                if (c == '\\' && p[1]) { p += 2; continue; }
                if (c == '"') in_str = 0;
            } else {
                if (c == '"') in_str = 1;
                else if (c == '[') depth++;
                else if (c == ']') { depth--; if (depth == 0) { p++; break; } }
            }
            p++;
        }
        size_t alen = (size_t)(p - arr_start);
        int match = (klen == tag_len) && html_iemem(k, tag, klen);
        if (match) {
            if (out_len) *out_len = alen;
            return arr_start;
        }
    }
    return NULL;
}

/* Returns 1 iff `attr` (length attr_len) appears as a string element
 * in the JSON array slice [arr, arr+arr_len). Comparison is case-
 * insensitive. */
static int html_attr_in_array(const char* arr, size_t arr_len,
                              const char* attr, size_t attr_len) {
    if (!arr || arr_len < 2) return 0;
    const char* p = arr + 1;
    const char* end = arr + arr_len - 1;
    while (p < end) {
        while (p < end && (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r' || *p == ',')) p++;
        if (p >= end) return 0;
        if (*p != '"') return 0;
        p++;
        const char* s = p;
        while (p < end && *p != '"') {
            if (*p == '\\' && p + 1 < end) p++;
            p++;
        }
        if (p >= end) return 0;
        size_t slen = (size_t)(p - s);
        p++;
        if (slen == attr_len && html_iemem(s, attr, slen)) return 1;
    }
    return 0;
}

/* Hard-coded set of tags whose content is ALSO dropped (entire subtree). */
static int html_is_dangerous_container(const char* tag, size_t tag_len) {
    static const char* names[] = {
        "script", "style", "iframe", "object", "embed", "form",
        "noscript", "noembed", "template", "svg", "math", "frame",
        "frameset", "applet", "audio", "video", "source", "track",
        NULL
    };
    for (int i = 0; names[i]; i++) {
        if (html_ieq_n(tag, tag_len, names[i])) return 1;
    }
    return 0;
}

/* HTML void elements — emit without a close tag. */
static int html_is_void(const char* tag, size_t tag_len) {
    static const char* names[] = {
        "area", "base", "br", "col", "embed", "hr", "img", "input",
        "link", "meta", "param", "source", "track", "wbr",
        NULL
    };
    for (int i = 0; names[i]; i++) {
        if (html_ieq_n(tag, tag_len, names[i])) return 1;
    }
    return 0;
}

/* Append a single byte HTML-escaped into the output buffer. */
static void html_escape_byte(html_buf_t* out, unsigned char c) {
    switch (c) {
        case '<':  html_buf_puts(out, "&lt;");   break;
        case '>':  html_buf_puts(out, "&gt;");   break;
        case '"':  html_buf_puts(out, "&quot;"); break;
        case '\'': html_buf_puts(out, "&#39;");  break;
        default:   html_buf_putc(out, (char)c);  break;
    }
}

/* Validate a URL value against the allowlist of safe schemes for hrefs.
 * Returns 1 iff the URL is safe to emit. Acceptable forms:
 *   - http:// or https:// (case-insensitive)
 *   - mailto:
 *   - fragment-only `#anchor`
 *   - relative path that does not contain a colon before the first
 *     slash/?/# (so `foo/bar`, `/foo`, `?x=1` are OK; `javascript:x` is
 *     not — its colon precedes any path/hash/query separator).
 *
 * URL leading whitespace and embedded ASCII control bytes (TAB, LF, CR)
 * are stripped before the scheme test, mirroring how browsers normalise
 * URLs (these bytes are otherwise a known XSS bypass: `java\tscript:`). */
static int html_url_is_safe(const char* url, size_t len) {
    if (!url || len == 0) return 1;  /* empty href is harmless */
    size_t i = 0;
    while (i < len) {
        unsigned char c = (unsigned char)url[i];
        if (c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == 0x0B || c == 0x0C) {
            i++; continue;
        }
        break;
    }
    if (i >= len) return 1;  /* whitespace only */
    if (url[i] == '#') return 1;  /* fragment only */
    if (url[i] == '/' || url[i] == '?') return 1;  /* relative */
    /* Find the first scheme-terminating character. */
    size_t scheme_end = (size_t)-1;
    for (size_t j = i; j < len; j++) {
        char c = url[j];
        if (c == ':') { scheme_end = j; break; }
        if (c == '/' || c == '?' || c == '#') break;
    }
    if (scheme_end == (size_t)-1) return 1;  /* no colon → relative path */
    /* Lowercase the scheme, stripping embedded control bytes. */
    char scheme[32];
    size_t sl = 0;
    for (size_t j = i; j < scheme_end && sl < sizeof(scheme) - 1; j++) {
        unsigned char c = (unsigned char)url[j];
        if (c == '\t' || c == '\n' || c == '\r' || c == 0x0B || c == 0x0C) continue;
        scheme[sl++] = (char)html_tolower(c);
    }
    scheme[sl] = '\0';
    if (strcmp(scheme, "http") == 0) return 1;
    if (strcmp(scheme, "https") == 0) return 1;
    if (strcmp(scheme, "mailto") == 0) return 1;
    return 0;
}

el_val_t el_html_sanitize(el_val_t input_v, el_val_t allowlist_v) {
    const char* input = EL_CSTR(input_v);
    const char* allow = EL_CSTR(allowlist_v);
    if (!input) return el_wrap_str(el_strdup(""));
    if (!allow) allow = "{}";
    size_t in_len = strlen(input);

    html_buf_t out;
    html_buf_init(&out);

    size_t i = 0;
    while (i < in_len) {
        unsigned char c = (unsigned char)input[i];
        if (c != '<') {
            /* Plain text — escape and emit. We pass `&` through verbatim
             * to preserve pre-encoded entities (`&lt;`, `&amp;`, `&#x...;`)
             * which the browser will decode safely. */
            if (c == '&') html_buf_putc(&out, '&');
            else          html_escape_byte(&out, c);
            i++;
            continue;
        }
        /* `<` — try to parse a tag. */
        if (i + 1 >= in_len) {
            html_buf_puts(&out, "&lt;");
            i++;
            continue;
        }
        /* Comments, doctype, CDATA, processing instructions — drop entirely. */
        if (input[i + 1] == '!') {
            if (i + 3 < in_len && input[i + 2] == '-' && input[i + 3] == '-') {
                size_t j = i + 4;
                while (j + 2 < in_len && !(input[j] == '-' && input[j + 1] == '-' && input[j + 2] == '>')) j++;
                if (j + 2 < in_len) i = j + 3;
                else i = in_len;
                continue;
            }
            size_t j = i + 2;
            while (j < in_len && input[j] != '>') j++;
            i = (j < in_len) ? j + 1 : in_len;
            continue;
        }
        if (input[i + 1] == '?') {
            size_t j = i + 2;
            while (j < in_len && input[j] != '>') j++;
            i = (j < in_len) ? j + 1 : in_len;
            continue;
        }
        int is_close = 0;
        size_t name_start = i + 1;
        if (input[i + 1] == '/') {
            is_close = 1;
            name_start = i + 2;
        }
        if (name_start >= in_len) {
            html_buf_puts(&out, "&lt;");
            i++;
            continue;
        }
        unsigned char nc = (unsigned char)input[name_start];
        if (!((nc >= 'a' && nc <= 'z') || (nc >= 'A' && nc <= 'Z'))) {
            /* `<` followed by non-letter — emit as escaped text. */
            html_buf_puts(&out, "&lt;");
            i++;
            continue;
        }
        size_t name_end = name_start;
        while (name_end < in_len) {
            unsigned char x = (unsigned char)input[name_end];
            if ((x >= 'a' && x <= 'z') || (x >= 'A' && x <= 'Z') ||
                (x >= '0' && x <= '9') || x == '-' || x == '_' || x == ':') {
                name_end++;
            } else {
                break;
            }
        }
        const char* tag = input + name_start;
        size_t tag_len = name_end - name_start;
        /* Find the `>` that closes this tag, respecting quoted attrs. */
        size_t cur = name_end;
        int self_close = 0;
        while (cur < in_len) {
            unsigned char x = (unsigned char)input[cur];
            if (x == '"' || x == '\'') {
                unsigned char q = x;
                cur++;
                while (cur < in_len && (unsigned char)input[cur] != q) cur++;
                if (cur < in_len) cur++;  /* skip closing quote */
                continue;
            }
            if (x == '/' && cur + 1 < in_len && input[cur + 1] == '>') {
                self_close = 1;
                break;
            }
            if (x == '>') break;
            cur++;
        }
        if (cur >= in_len) {
            /* Malformed: unclosed tag at EOF. Drop the rest of the input. */
            i = in_len;
            continue;
        }
        size_t tag_end = self_close ? cur + 2 : cur + 1;  /* one past `>` */
        /* Dangerous container — drop the whole subtree. */
        if (!is_close && html_is_dangerous_container(tag, tag_len)) {
            if (self_close || html_is_void(tag, tag_len)) {
                i = tag_end;
                continue;
            }
            size_t scan = tag_end;
            int found_close = 0;
            while (scan < in_len) {
                if (input[scan] != '<') { scan++; continue; }
                if (scan + 1 < in_len && input[scan + 1] == '/') {
                    size_t cn_start = scan + 2;
                    size_t cn_end = cn_start;
                    while (cn_end < in_len) {
                        unsigned char x = (unsigned char)input[cn_end];
                        if ((x >= 'a' && x <= 'z') || (x >= 'A' && x <= 'Z') ||
                            (x >= '0' && x <= '9') || x == '-' || x == '_' || x == ':') {
                            cn_end++;
                        } else break;
                    }
                    if (cn_end - cn_start == tag_len &&
                        html_iemem(input + cn_start, tag, tag_len)) {
                        size_t end_close = cn_end;
                        while (end_close < in_len && input[end_close] != '>') end_close++;
                        i = (end_close < in_len) ? end_close + 1 : in_len;
                        found_close = 1;
                        break;
                    }
                }
                scan++;
            }
            if (!found_close) {
                /* No matching close — drop everything from here on. */
                i = in_len;
            }
            continue;
        }
        /* Look up the tag in the allowlist. */
        size_t arr_len = 0;
        const char* arr = html_allowlist_find(allow, tag, tag_len, &arr_len);
        if (!arr) {
            /* Tag not allowed. Drop the open/close marker; inner text is
             * processed by the outer loop and re-emitted as escaped text. */
            i = tag_end;
            continue;
        }
        if (is_close) {
            if (!html_is_void(tag, tag_len)) {
                html_buf_putc(&out, '<');
                html_buf_putc(&out, '/');
                for (size_t k = 0; k < tag_len; k++) {
                    html_buf_putc(&out, (char)html_tolower((unsigned char)tag[k]));
                }
                html_buf_putc(&out, '>');
            }
            i = tag_end;
            continue;
        }
        /* Allowed open tag. Emit `<name` and walk the attributes between
         * `name_end` and the closing `>`. */
        html_buf_putc(&out, '<');
        for (size_t k = 0; k < tag_len; k++) {
            html_buf_putc(&out, (char)html_tolower((unsigned char)tag[k]));
        }
        size_t a = name_end;
        while (a < cur) {
            unsigned char x = (unsigned char)input[a];
            if (x == ' ' || x == '\t' || x == '\n' || x == '\r' || x == '/') { a++; continue; }
            size_t an_start = a;
            while (a < cur) {
                unsigned char y = (unsigned char)input[a];
                if (y == '=' || y == ' ' || y == '\t' || y == '\n' || y == '\r' || y == '/' || y == '>') break;
                a++;
            }
            size_t an_len = a - an_start;
            if (an_len == 0) { a++; continue; }
            size_t av_start = 0;
            size_t av_len = 0;
            int has_value = 0;
            size_t b = a;
            while (b < cur && (input[b] == ' ' || input[b] == '\t' || input[b] == '\n' || input[b] == '\r')) b++;
            if (b < cur && input[b] == '=') {
                has_value = 1;
                b++;
                while (b < cur && (input[b] == ' ' || input[b] == '\t' || input[b] == '\n' || input[b] == '\r')) b++;
                if (b < cur && (input[b] == '"' || input[b] == '\'')) {
                    unsigned char q = (unsigned char)input[b];
                    b++;
                    av_start = b;
                    while (b < cur && (unsigned char)input[b] != q) b++;
                    av_len = b - av_start;
                    if (b < cur) b++;
                } else {
                    av_start = b;
                    while (b < cur) {
                        unsigned char y = (unsigned char)input[b];
                        if (y == ' ' || y == '\t' || y == '\n' || y == '\r' || y == '>') break;
                        b++;
                    }
                    av_len = b - av_start;
                }
                a = b;
            }
            if (!html_attr_in_array(arr, arr_len, input + an_start, an_len)) continue;
            int is_href = (an_len == 4 && html_iemem(input + an_start, "href", 4));
            int is_src  = (an_len == 3 && html_iemem(input + an_start, "src",  3));
            if ((is_href || is_src) && has_value) {
                if (!html_url_is_safe(input + av_start, av_len)) continue;
            }
            html_buf_putc(&out, ' ');
            for (size_t k = 0; k < an_len; k++) {
                html_buf_putc(&out, (char)html_tolower((unsigned char)input[an_start + k]));
            }
            if (has_value) {
                html_buf_puts(&out, "=\"");
                for (size_t k = 0; k < av_len; k++) {
                    unsigned char y = (unsigned char)input[av_start + k];
                    /* Re-escape so the emitted attribute is well-formed
                     * double-quoted HTML. `&` passes through to preserve
                     * pre-encoded entities. */
                    if (y == '"')      html_buf_puts(&out, "&quot;");
                    else if (y == '<') html_buf_puts(&out, "&lt;");
                    else if (y == '>') html_buf_puts(&out, "&gt;");
                    else                html_buf_putc(&out, (char)y);
                }
                html_buf_putc(&out, '"');
            }
        }
        html_buf_putc(&out, '>');
        i = tag_end;
    }
    /* Copy into arena-tracked buffer so the standard runtime memory model
     * applies to the returned string. */
    char* result = el_strbuf(out.len);
    memcpy(result, out.data, out.len);
    result[out.len] = '\0';
    html_buf_free(&out);
    return el_wrap_str(result);
}

/* ── JSON ────────────────────────────────────────────────────────────────── */

/* True iff the segment is non-empty and every byte is an ASCII digit. We treat
 * such segments as numeric array indices when walking a dot-path; mixed names
 * like "0a" remain object-key lookups, so a key named "0" still wins over an
 * index when the surrounding container is an object. */
static int json_path_seg_is_index(const char* seg, size_t n) {
    if (n == 0) return 0;
    for (size_t i = 0; i < n; i++) {
        if (seg[i] < '0' || seg[i] > '9') return 0;
    }
    return 1;
}

/* Skip JSON whitespace. */
static const char* json_skip_ws(const char* p) {
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    return p;
}

/* Descend one segment into the JSON cursor `p`.
 *   - If `p` points at an array `[...]` and the segment is all digits,
 *     advance to that element (zero-based).
 *   - Otherwise treat the segment as an object key and use json_find_key
 *     scoped to a one-level slice of the current container.
 * Returns NULL if the descent fails (segment not found, container mismatch).
 *
 * `seg` is a pointer into the original path string and `seg_len` is its
 * byte length — this avoids an extra alloc per segment. */
static const char* json_path_descend(const char* p, const char* seg, size_t seg_len) {
    if (!p || !seg) return NULL;
    p = json_skip_ws(p);
    if (*p == '[' && json_path_seg_is_index(seg, seg_len)) {
        long idx = 0;
        for (size_t i = 0; i < seg_len; i++) idx = idx * 10 + (seg[i] - '0');
        p++;  /* step past '[' */
        p = json_skip_ws(p);
        long cur = 0;
        while (*p && *p != ']') {
            if (cur == idx) return p;
            const char* end = json_skip_value(p);
            if (!end || end == p) return NULL;
            p = json_skip_ws(end);
            if (*p == ',') { p++; p = json_skip_ws(p); cur++; continue; }
            /* No comma after this element — only acceptable at the closing ']',
             * which means we ran out of elements. */
            break;
        }
        return NULL;
    }
    /* Object lookup. json_find_key walks at depth 1 of whatever container it
     * receives, so we slice from `p` onwards. Caller already positioned us at
     * the opening '{' (or at whitespace before it). */
    if (*p != '{') return NULL;
    /* Build a NUL-terminated copy of the key segment for the lookup. We only
     * pay this cost when the segment isn't a numeric index. */
    char stack_key[256];
    char* k = stack_key;
    if (seg_len + 1 > sizeof(stack_key)) {
        k = malloc(seg_len + 1);
        if (!k) return NULL;
    }
    memcpy(k, seg, seg_len);
    k[seg_len] = '\0';
    const char* found = json_find_key(p, k);
    if (k != stack_key) free(k);
    return found;
}

/* Read the JSON value at `p` into a freshly-allocated, arena-owned el_val_t.
 *   - String  -> unescaped, wrapped el_val_t string
 *   - Anything else -> raw JSON slice as a string (matches the historical
 *     json_get behaviour: numbers/bools/null come back stringified). */
static el_val_t json_read_value(const char* p) {
    p = json_skip_ws(p);
    if (*p == '"') {
        p++;
        size_t cap = strlen(p) + 1;
        char* out = el_strbuf(cap);
        char* w = out;
        while (*p && *p != '"') {
            if (*p == '\\' && *(p+1)) {
                p++;
                switch (*p) {
                    case '"':  *w++ = '"';  break;
                    case '\\': *w++ = '\\'; break;
                    case '/':  *w++ = '/';  break;
                    case 'n':  *w++ = '\n'; break;
                    case 'r':  *w++ = '\r'; break;
                    case 't':  *w++ = '\t'; break;
                    default:   *w++ = *p;   break;
                }
            } else {
                *w++ = *p;
            }
            p++;
        }
        *w = '\0';
        return el_wrap_str(out);
    }
    /* Object/array/number/bool/null — return the raw slice up to the value's
     * end. json_skip_value tracks brace/bracket/string state so nested objects
     * round-trip cleanly. */
    const char* end = json_skip_value(p);
    if (!end) end = p;
    size_t n = (size_t)(end - p);
    /* Strip trailing whitespace from scalar values so callers don't see
     * `123 ` when they parsed a pretty-printed number. */
    while (n > 0 && (p[n-1] == ' ' || p[n-1] == '\t' || p[n-1] == '\n' || p[n-1] == '\r')) {
        n--;
    }
    char* out = el_strbuf(n);
    memcpy(out, p, n);
    out[n] = '\0';
    return el_wrap_str(out);
}

el_val_t json_get(el_val_t jsonv, el_val_t keyv) {
    const char* json = EL_CSTR(jsonv);
    const char* key  = EL_CSTR(keyv);
    if (!json || !key) return el_wrap_str(el_strdup(""));

    /* Fast path: key contains no '.' — keep the historical single-segment
     * substring search so existing callers retain their O(strlen) cost
     * profile. The dot-path walker is only paid for when needed. */
    if (!strchr(key, '.')) {
        size_t klen = strlen(key);
        char stack_pat[512];
        char* pattern;
        if (klen + 5 <= sizeof(stack_pat)) {
            pattern = stack_pat;
        } else {
            pattern = malloc(klen + 5);
            if (!pattern) return el_wrap_str(el_strdup(""));
        }
        snprintf(pattern, klen + 5, "\"%s\":", key);
        const char* p = strstr(json, pattern);
        if (pattern != stack_pat) free(pattern);
        if (!p) return el_wrap_str(el_strdup(""));
        p += strlen(key) + 3; /* skip "key": */
        return json_read_value(p);
    }

    /* Dot-path traversal. Walk segments left to right; at each step, descend
     * into the current container by either array index (all-digit segment on
     * an array cursor) or object key. */
    const char* cursor = json_skip_ws(json);
    const char* seg_start = key;
    const char* k = key;
    while (1) {
        if (*k == '.' || *k == '\0') {
            size_t seg_len = (size_t)(k - seg_start);
            cursor = json_path_descend(cursor, seg_start, seg_len);
            if (!cursor) return el_wrap_str(el_strdup(""));
            if (*k == '\0') break;
            k++;
            seg_start = k;
            continue;
        }
        k++;
    }
    return json_read_value(cursor);
}

/* ── Float bit-cast helpers ──────────────────────────────────────────────── */
/* `el_to_float` and `el_from_float` are exposed in el_runtime.h as static
 * inlines so generated programs (which #include the header) can call them
 * for Float literals. No definitions are needed here. */

/* ── JSON parser (recursive descent) ─────────────────────────────────────── */
/*
 * Parsed JSON representation:
 *   - object  -> ElMap (keys & values are el_val_t)
 *   - array   -> ElList
 *   - string  -> EL_STR-wrapped char* (allocated)
 *   - number  -> int (el_val_t) if integer, otherwise el_from_float(double)
 *   - true    -> 1
 *   - false   -> 0
 *   - null    -> EL_NULL (0)
 *
 * Note: there is no runtime type tag — parsed numbers cannot be
 * distinguished from booleans by the runtime alone. The codegen tracks
 * types separately. This matches the rest of el_val_t's type-erased model.
 */

/* JsonParser struct is forward-declared near the HTTP/Engram section. */

static void jp_skip_ws(JsonParser* jp) {
    while (jp->p < jp->end) {
        char c = *jp->p;
        if (c == ' ' || c == '\t' || c == '\n' || c == '\r') jp->p++;
        else break;
    }
}

static el_val_t jp_parse_value(JsonParser* jp);

/* Parse a JSON string literal (the opening " has NOT yet been consumed). */
static char* jp_parse_string_raw(JsonParser* jp) {
    if (jp->p >= jp->end || *jp->p != '"') { jp->err = 1; return el_strdup(""); }
    jp->p++;
    size_t cap = 32, len = 0;
    char* out = malloc(cap);
    if (!out) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    while (jp->p < jp->end && *jp->p != '"') {
        char c = *jp->p++;
        if (c == '\\' && jp->p < jp->end) {
            char esc = *jp->p++;
            switch (esc) {
                case '"':  c = '"';  break;
                case '\\': c = '\\'; break;
                case '/':  c = '/';  break;
                case 'b':  c = '\b'; break;
                case 'f':  c = '\f'; break;
                case 'n':  c = '\n'; break;
                case 'r':  c = '\r'; break;
                case 't':  c = '\t'; break;
                case 'u': {
                    /* Skip 4 hex digits; emit '?' as a placeholder */
                    for (int i = 0; i < 4 && jp->p < jp->end; i++) jp->p++;
                    c = '?';
                    break;
                }
                default: c = esc; break;
            }
        }
        if (len + 1 >= cap) {
            cap *= 2;
            out = realloc(out, cap);
            if (!out) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
        }
        out[len++] = c;
    }
    if (jp->p < jp->end && *jp->p == '"') jp->p++;
    else jp->err = 1;
    out[len] = '\0';
    return out;
}

static el_val_t jp_parse_number(JsonParser* jp) {
    const char* start = jp->p;
    int is_float = 0;
    if (jp->p < jp->end && (*jp->p == '-' || *jp->p == '+')) jp->p++;
    while (jp->p < jp->end && isdigit((unsigned char)*jp->p)) jp->p++;
    if (jp->p < jp->end && *jp->p == '.') {
        is_float = 1; jp->p++;
        while (jp->p < jp->end && isdigit((unsigned char)*jp->p)) jp->p++;
    }
    if (jp->p < jp->end && (*jp->p == 'e' || *jp->p == 'E')) {
        is_float = 1; jp->p++;
        if (jp->p < jp->end && (*jp->p == '+' || *jp->p == '-')) jp->p++;
        while (jp->p < jp->end && isdigit((unsigned char)*jp->p)) jp->p++;
    }
    size_t n = (size_t)(jp->p - start);
    char buf[64];
    if (n >= sizeof(buf)) n = sizeof(buf) - 1;
    memcpy(buf, start, n);
    buf[n] = '\0';
    if (is_float) return el_from_float(strtod(buf, NULL));
    return (el_val_t)strtoll(buf, NULL, 10);
}

static el_val_t jp_parse_array(JsonParser* jp) {
    if (jp->p < jp->end && *jp->p == '[') jp->p++;
    el_val_t lst = el_list_empty();
    jp_skip_ws(jp);
    if (jp->p < jp->end && *jp->p == ']') { jp->p++; return lst; }
    while (jp->p < jp->end) {
        jp_skip_ws(jp);
        el_val_t v = jp_parse_value(jp);
        lst = el_list_append(lst, v);
        jp_skip_ws(jp);
        if (jp->p < jp->end && *jp->p == ',') { jp->p++; continue; }
        if (jp->p < jp->end && *jp->p == ']') { jp->p++; break; }
        jp->err = 1;
        break;
    }
    return lst;
}

static el_val_t jp_parse_object(JsonParser* jp) {
    if (jp->p < jp->end && *jp->p == '{') jp->p++;
    el_val_t m = el_map_new(0);
    jp_skip_ws(jp);
    if (jp->p < jp->end && *jp->p == '}') { jp->p++; return m; }
    while (jp->p < jp->end) {
        jp_skip_ws(jp);
        char* key = jp_parse_string_raw(jp);
        jp_skip_ws(jp);
        if (jp->p < jp->end && *jp->p == ':') jp->p++;
        else { jp->err = 1; free(key); break; }
        jp_skip_ws(jp);
        el_val_t v = jp_parse_value(jp);
        m = el_map_set(m, EL_STR(key), v);
        jp_skip_ws(jp);
        if (jp->p < jp->end && *jp->p == ',') { jp->p++; continue; }
        if (jp->p < jp->end && *jp->p == '}') { jp->p++; break; }
        jp->err = 1;
        break;
    }
    return m;
}

static el_val_t jp_parse_value(JsonParser* jp) {
    jp_skip_ws(jp);
    if (jp->p >= jp->end) { jp->err = 1; return EL_NULL; }
    char c = *jp->p;
    if (c == '"') return el_wrap_str(jp_parse_string_raw(jp));
    if (c == '{') return jp_parse_object(jp);
    if (c == '[') return jp_parse_array(jp);
    if (c == '-' || isdigit((unsigned char)c)) return jp_parse_number(jp);
    if (c == 't' && jp->p + 4 <= jp->end && strncmp(jp->p, "true", 4) == 0) { jp->p += 4; return 1; }
    if (c == 'f' && jp->p + 5 <= jp->end && strncmp(jp->p, "false", 5) == 0) { jp->p += 5; return 0; }
    if (c == 'n' && jp->p + 4 <= jp->end && strncmp(jp->p, "null", 4) == 0) { jp->p += 4; return EL_NULL; }
    jp->err = 1;
    return EL_NULL;
}

el_val_t json_parse(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return EL_NULL;
    JsonParser jp = { .p = s, .end = s + strlen(s), .err = 0 };
    el_val_t v = jp_parse_value(&jp);
    if (jp.err) return EL_NULL;
    return v;
}

/* ── JSON stringify ──────────────────────────────────────────────────────── */
/*
 * Stringify policy: el_val_t is type-erased, so we cannot perfectly
 * round-trip arbitrary values. We use these heuristics:
 *   - If value is an ElList pointer (in the heap range), serialize as array.
 *   - If value is an ElMap pointer, serialize as object.
 *   - If value looks like a printable string pointer, serialize as string.
 *   - Otherwise serialize as integer.
 * This is best-effort. Programs that need exact control should build the
 * string directly. A pointer test is the cheapest way to disambiguate
 * from small integers without a separate type tag.
 */

/* JsonBuf struct is forward-declared near the HTTP section so HTTP helpers
 * can use it. Its definition appears there. */

static void jb_init(JsonBuf* b) {
    b->cap = 64; b->len = 0;
    b->buf = malloc(b->cap);
    if (!b->buf) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    b->buf[0] = '\0';
}

static void jb_reserve(JsonBuf* b, size_t add) {
    if (b->len + add + 1 > b->cap) {
        while (b->len + add + 1 > b->cap) b->cap *= 2;
        b->buf = realloc(b->buf, b->cap);
        if (!b->buf) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    }
}

static void jb_putc(JsonBuf* b, char c) {
    jb_reserve(b, 1);
    b->buf[b->len++] = c;
    b->buf[b->len] = '\0';
}

static void jb_puts(JsonBuf* b, const char* s) {
    size_t n = strlen(s);
    jb_reserve(b, n);
    memcpy(b->buf + b->len, s, n);
    b->len += n;
    b->buf[b->len] = '\0';
}

static void jb_emit_escaped(JsonBuf* b, const char* s) {
    jb_putc(b, '"');
    for (; *s; s++) {
        unsigned char c = (unsigned char)*s;
        switch (c) {
            case '"':  jb_puts(b, "\\\""); break;
            case '\\': jb_puts(b, "\\\\"); break;
            case '\b': jb_puts(b, "\\b");  break;
            case '\f': jb_puts(b, "\\f");  break;
            case '\n': jb_puts(b, "\\n");  break;
            case '\r': jb_puts(b, "\\r");  break;
            case '\t': jb_puts(b, "\\t");  break;
            default:
                if (c < 0x20) {
                    char tmp[8];
                    snprintf(tmp, sizeof(tmp), "\\u%04x", c);
                    jb_puts(b, tmp);
                } else {
                    jb_putc(b, (char)c);
                }
                break;
        }
    }
    jb_putc(b, '"');
}

/* Heuristic: is this el_val_t likely a pointer to an ElList?
 * We can't fully verify, but pointers are large addresses, integers small.
 * Treat values whose magnitude exceeds 2^32 as potential pointers and
 * sniff by reading the header conservatively.
 *
 * Simpler heuristic: if the value reads as a printable string, treat as
 * string; otherwise as integer. Lists/Maps are encoded as struct pointers,
 * which have leading binary bytes — so they won't look like strings. */

static int looks_like_string(el_val_t v) {
    if (v == 0) return 0;
    /* Treat plausible heap addresses as candidates.
     * Threshold: 4 GiB (0x100000000). On 64-bit systems heap addresses from
     * malloc/mmap start well above 4 GiB (ASLR pushes them to ~0x7f...).
     * El integer values (counters, unix timestamps up to ~2106) all fit below
     * 0x100000000 (4294967296). The old threshold of 1,000,000 caused unix
     * timestamps (~1.7e9) to be misidentified as string pointers — a segfault
     * risk in json_stringify and jb_emit_value. */
    uintptr_t p = (uintptr_t)v;
    if (p < 0x100000000ULL) return 0;   /* integers, timestamps, counters */
    if (p < 0x1000) return 0;
    /* Sniff first bytes for printable */
    const unsigned char* s = (const unsigned char*)p;
    for (int i = 0; i < 16; i++) {
        unsigned char c = s[i];
        if (c == '\0') return 1; /* terminated string (empty string is still a valid string) */
        /* Reject C0 control chars (non-whitespace), allow UTF-8 high bytes.
         * 0x09-0x0d = tab/newline/cr/vt/ff (whitespace, OK)
         * 0x20-0x7e = printable ASCII (OK)
         * 0x7f      = DEL (reject)
         * 0x80-0xff = UTF-8 continuation/lead bytes (OK for multi-byte chars) */
        if (c < 0x09 || (c > 0x0d && c < 0x20) || c == 0x7f) return 0;
    }
    return 1; /* 16+ printable bytes — call it a string */
}

static void jb_emit_value(JsonBuf* b, el_val_t v);

static void jb_emit_int(JsonBuf* b, int64_t n) {
    char tmp[32];
    snprintf(tmp, sizeof(tmp), "%lld", (long long)n);
    jb_puts(b, tmp);
}

static void jb_emit_value(JsonBuf* b, el_val_t v) {
    if (v == EL_NULL) { jb_puts(b, "null"); return; }
    if (looks_like_string(v)) {
        jb_emit_escaped(b, EL_CSTR(v));
        return;
    }
    jb_emit_int(b, (int64_t)v);
}

el_val_t json_stringify(el_val_t v) {
    JsonBuf b; jb_init(&b);
    jb_emit_value(&b, v);
    return el_wrap_str(b.buf);
}

/* ── JSON substring accessors ────────────────────────────────────────────── */
/*
 * These walk the raw JSON string looking for "key": at the top level (depth 1)
 * of an object. They handle escaped quotes, nested objects/arrays, and
 * whitespace around the colon.
 */

/* Find "key": at object-depth == 1 inside the JSON object string `s`.
 * Returns pointer to the first byte of the value, or NULL.            */
static const char* json_find_key(const char* s, const char* key) {
    if (!s || !key) return NULL;
    size_t klen = strlen(key);
    int depth = 0;
    int in_str = 0;
    int escape = 0;
    const char* p = s;
    while (*p) {
        char c = *p;
        if (in_str) {
            if (escape) { escape = 0; }
            else if (c == '\\') { escape = 1; }
            else if (c == '"') {
                /* End of string. If we're at depth 1, check if this was a key. */
                p++;
                if (depth == 1) {
                    /* The string just ended at p-1. Check if it matches key
                     * and is followed by a colon. We need to backtrack to find
                     * the start of this string and compare. */
                }
                in_str = 0;
                continue;
            }
            p++;
            continue;
        }
        if (c == '"') {
            /* Start of a string literal */
            const char* str_start = p + 1;
            const char* q = str_start;
            int e = 0;
            while (*q) {
                if (e) { e = 0; q++; continue; }
                if (*q == '\\') { e = 1; q++; continue; }
                if (*q == '"') break;
                q++;
            }
            size_t slen = (size_t)(q - str_start);
            const char* after = (*q == '"') ? q + 1 : q;
            /* If at depth 1 and matches key and followed by ':' -> got it */
            if (depth == 1 && slen == klen && strncmp(str_start, key, klen) == 0) {
                const char* r = after;
                while (*r == ' ' || *r == '\t' || *r == '\n' || *r == '\r') r++;
                if (*r == ':') {
                    r++;
                    while (*r == ' ' || *r == '\t' || *r == '\n' || *r == '\r') r++;
                    return r;
                }
            }
            p = after;
            continue;
        }
        if (c == '{' || c == '[') depth++;
        else if (c == '}' || c == ']') depth--;
        p++;
    }
    return NULL;
}

/* Skip a JSON value starting at p; return pointer past the value end.   */
static const char* json_skip_value(const char* p) {
    if (!p || !*p) return p;
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (*p == '"') {
        p++;
        int e = 0;
        while (*p) {
            if (e) { e = 0; p++; continue; }
            if (*p == '\\') { e = 1; p++; continue; }
            if (*p == '"') { p++; break; }
            p++;
        }
        return p;
    }
    if (*p == '{' || *p == '[') {
        char open  = *p;
        char close = (open == '{') ? '}' : ']';
        int depth = 0;
        int in_str = 0;
        int e = 0;
        while (*p) {
            char c = *p;
            if (in_str) {
                if (e) { e = 0; }
                else if (c == '\\') { e = 1; }
                else if (c == '"') in_str = 0;
                p++;
                continue;
            }
            if (c == '"') { in_str = 1; p++; continue; }
            if (c == open) depth++;
            else if (c == close) { depth--; p++; if (depth == 0) return p; continue; }
            p++;
        }
        return p;
    }
    /* scalar: number, true/false/null */
    while (*p && *p != ',' && *p != '}' && *p != ']' &&
           *p != ' ' && *p != '\t' && *p != '\n' && *p != '\r') p++;
    return p;
}

el_val_t json_get_string(el_val_t json_str, el_val_t key) {
    const char* json = EL_CSTR(json_str);
    const char* k    = EL_CSTR(key);
    const char* p = json_find_key(json, k);
    if (!p || *p != '"') return el_wrap_str(el_strdup(""));
    p++;
    JsonParser jp = { .p = p - 1, .end = json + (json ? strlen(json) : 0), .err = 0 };
    char* parsed = jp_parse_string_raw(&jp);
    if (jp.err) { free(parsed); return el_wrap_str(el_strdup("")); }
    return el_wrap_str(parsed);
}

el_val_t json_get_int(el_val_t json_str, el_val_t key) {
    const char* json = EL_CSTR(json_str);
    const char* k    = EL_CSTR(key);
    const char* p = json_find_key(json, k);
    if (!p) return 0;
    if (*p == '"' || *p == '{' || *p == '[') return 0;
    return (el_val_t)strtoll(p, NULL, 10);
}

el_val_t json_get_float(el_val_t json_str, el_val_t key) {
    const char* json = EL_CSTR(json_str);
    const char* k    = EL_CSTR(key);
    const char* p = json_find_key(json, k);
    if (!p) return 0;
    if (*p == '"' || *p == '{' || *p == '[') return 0;
    return el_from_float(strtod(p, NULL));
}

el_val_t json_get_bool(el_val_t json_str, el_val_t key) {
    const char* json = EL_CSTR(json_str);
    const char* k    = EL_CSTR(key);
    const char* p = json_find_key(json, k);
    if (!p) return 0;
    if (strncmp(p, "true", 4) == 0) return 1;
    return 0;
}

el_val_t json_get_raw(el_val_t json_str, el_val_t key) {
    const char* json = EL_CSTR(json_str);
    const char* k    = EL_CSTR(key);
    const char* p = json_find_key(json, k);
    /* Clear fs_read binary-length hint — result is a fresh null-terminated
     * string, not the raw file bytes, so Content-Length must use strlen. */
    _tl_fs_read_len = 0;
    if (!p) return el_wrap_str(el_strdup(""));
    const char* end = json_skip_value(p);
    size_t n = (size_t)(end - p);
    char* out = el_strbuf(n);
    memcpy(out, p, n);
    out[n] = '\0';
    return el_wrap_str(out);
}

el_val_t json_set(el_val_t json_str, el_val_t key, el_val_t value) {
    const char* json = EL_CSTR(json_str);
    const char* k    = EL_CSTR(key);
    /* raw_val is the JSON value as-is (already encoded by the caller).
     * If it looks like a plain (non-JSON) string, wrap it as a JSON string.
     * Convention: callers pass pre-encoded values like "\"bob\"" for strings,
     * "42" for numbers, "true"/"false" for booleans. */
    const char* raw_val = EL_CSTR(value);
    if (!k) k = "";
    if (!raw_val) raw_val = "null";
    if (!json || !*json) {
        /* Build a fresh object */
        JsonBuf b; jb_init(&b);
        jb_putc(&b, '{');
        jb_emit_escaped(&b, k);
        jb_putc(&b, ':');
        jb_puts(&b, raw_val);
        jb_putc(&b, '}');
        return el_wrap_str(b.buf);
    }
    const char* existing = json_find_key(json, k);
    JsonBuf b; jb_init(&b);
    if (existing) {
        const char* end = json_skip_value(existing);
        /* Copy [json .. existing) */
        size_t prefix = (size_t)(existing - json);
        jb_reserve(&b, prefix);
        memcpy(b.buf + b.len, json, prefix);
        b.len += prefix;
        b.buf[b.len] = '\0';
        jb_puts(&b, raw_val);
        jb_puts(&b, end);
        return el_wrap_str(b.buf);
    }
    /* Insert before closing '}'. Find last '}' */
    size_t jl = strlen(json);
    if (jl == 0) { free(b.buf); return el_wrap_str(el_strdup("{}")); }
    /* Find last '}' from the end */
    ssize_t close_idx = -1;
    for (ssize_t i = (ssize_t)jl - 1; i >= 0; i--) {
        if (json[i] == '}') { close_idx = i; break; }
    }
    if (close_idx < 0) {
        free(b.buf);
        return el_wrap_str(el_strdup(json));
    }
    /* Determine if object is empty: scan between last '{' and '}' for non-ws */
    int empty = 1;
    for (ssize_t i = close_idx - 1; i >= 0; i--) {
        char c = json[i];
        if (c == '{') break;
        if (c != ' ' && c != '\t' && c != '\n' && c != '\r') { empty = 0; break; }
    }
    /* Copy json[0..close_idx) */
    jb_reserve(&b, (size_t)close_idx);
    memcpy(b.buf + b.len, json, (size_t)close_idx);
    b.len += (size_t)close_idx;
    b.buf[b.len] = '\0';
    if (!empty) jb_putc(&b, ',');
    jb_emit_escaped(&b, k);
    jb_putc(&b, ':');
    jb_puts(&b, raw_val);
    /* Append from close_idx onward */
    jb_puts(&b, json + close_idx);
    return el_wrap_str(b.buf);
}

el_val_t json_array_len(el_val_t json_str) {
    const char* s = EL_CSTR(json_str);
    if (!s) return 0;
    while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++;
    if (*s != '[') return 0;
    s++;
    while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++;
    if (*s == ']') return 0;
    int64_t count = 0;
    while (*s) {
        const char* end = json_skip_value(s);
        if (end == s) break;
        count++;
        s = end;
        while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++;
        if (*s == ',') { s++; continue; }
        if (*s == ']' || *s == '\0') break;
    }
    return (el_val_t)count;
}

/* json_array_get — return the i-th element of a JSON array as a JSON
 * fragment string. Nested objects and arrays are returned verbatim
 * (json_skip_value tracks brace/bracket depth so nested structures are
 * preserved intact). Out-of-range index → "". */
el_val_t json_array_get(el_val_t json_str, el_val_t index) {
    const char* s = EL_CSTR(json_str);
    int64_t  idx = (int64_t)index;
    if (!s || idx < 0) return el_wrap_str(el_strdup(""));
    while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++;
    if (*s != '[') return el_wrap_str(el_strdup(""));
    s++;
    while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++;
    if (*s == ']') return el_wrap_str(el_strdup(""));
    int64_t i = 0;
    while (*s) {
        const char* start = s;
        const char* end   = json_skip_value(s);
        if (end == s) break;
        if (i == idx) {
            size_t n = (size_t)(end - start);
            char* out = el_strbuf(n);
            memcpy(out, start, n);
            out[n] = '\0';
            return el_wrap_str(out);
        }
        i++;
        s = end;
        while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++;
        if (*s == ',') { s++; while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++; continue; }
        if (*s == ']' || *s == '\0') break;
    }
    return el_wrap_str(el_strdup(""));
}

/* json_array_get_string — same as json_array_get, but assume the element
 * is a JSON string and return the unquoted/unescaped value. Non-string
 * elements yield "". */
el_val_t json_array_get_string(el_val_t json_str, el_val_t index) {
    el_val_t raw = json_array_get(json_str, index);
    const char* s = EL_CSTR(raw);
    if (!s || *s != '"') return el_wrap_str(el_strdup(""));
    JsonParser jp = {
        .p   = s,
        .end = s + strlen(s),
        .err = 0,
    };
    char* parsed = jp_parse_string_raw(&jp);
    if (jp.err) {
        free(parsed);
        return el_wrap_str(el_strdup(""));
    }
    return el_wrap_str(parsed);
}

/* json_escape_string — escape a string value for embedding in JSON.
 * Returns the escaped content WITHOUT surrounding quotes.
 * "say \"hello\"" -> "say \\\"hello\\\""  */
el_val_t json_escape_string(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return el_wrap_str(el_strdup(""));
    size_t n = strlen(s);
    /* Worst case: every char needs a 2-char escape. */
    char* out = malloc(n * 2 + 1);
    if (!out) return el_wrap_str(el_strdup(""));
    size_t j = 0;
    for (size_t i = 0; i < n; i++) {
        unsigned char c = (unsigned char)s[i];
        if      (c == '"')  { out[j++] = '\\'; out[j++] = '"'; }
        else if (c == '\\') { out[j++] = '\\'; out[j++] = '\\'; }
        else if (c == '\n') { out[j++] = '\\'; out[j++] = 'n'; }
        else if (c == '\r') { out[j++] = '\\'; out[j++] = 'r'; }
        else if (c == '\t') { out[j++] = '\\'; out[j++] = 't'; }
        else { out[j++] = (char)c; }
    }
    out[j] = '\0';
    el_val_t result = el_wrap_str(el_strdup(out));
    free(out);
    return result;
}

/* json_build_object — build a JSON object from a flat key-value list.
 * kvs is [key0, val0, key1, val1, ...]. Values are raw JSON (pass
 * strings as "\"value\"" or use json_escape_string). */
el_val_t json_build_object(el_val_t kvs) {
    el_val_t list = kvs;
    int64_t n = el_list_len(list);
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '{');
    int first = 1;
    for (int64_t i = 0; i + 1 < n; i += 2) {
        el_val_t k = el_list_get(list, (el_val_t)i);
        el_val_t v = el_list_get(list, (el_val_t)(i + 1));
        const char* ks = EL_CSTR(k);
        const char* vs = EL_CSTR(v);
        if (!ks || !vs) continue;
        if (!first) jb_putc(&b, ',');
        first = 0;
        jb_putc(&b, '"');
        jb_puts(&b, ks);
        jb_puts(&b, "\":\"");
        /* escape the value string */
        size_t vn = strlen(vs);
        for (size_t j = 0; j < vn; j++) {
            unsigned char c = (unsigned char)vs[j];
            if      (c == '"')  { jb_putc(&b, '\\'); jb_putc(&b, '"'); }
            else if (c == '\\') { jb_putc(&b, '\\'); jb_putc(&b, '\\'); }
            else if (c == '\n') { jb_putc(&b, '\\'); jb_putc(&b, 'n'); }
            else if (c == '\r') { jb_putc(&b, '\\'); jb_putc(&b, 'r'); }
            else if (c == '\t') { jb_putc(&b, '\\'); jb_putc(&b, 't'); }
            else { jb_putc(&b, (char)c); }
        }
        jb_putc(&b, '"');
    }
    jb_putc(&b, '}');
    return el_wrap_str(b.buf);
}

/* json_build_array — build a JSON array from a list of raw JSON values.
 * items is ["\"alpha\"", "\"beta\"", "42", "true", ...]. */
el_val_t json_build_array(el_val_t items) {
    el_val_t list = items;
    int64_t n = el_list_len(list);
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '[');
    for (int64_t i = 0; i < n; i++) {
        el_val_t v = el_list_get(list, (el_val_t)i);
        const char* vs = EL_CSTR(v);
        if (!vs) continue;
        if (i > 0) jb_putc(&b, ',');
        jb_puts(&b, vs);
    }
    jb_putc(&b, ']');
    return el_wrap_str(b.buf);
}

/* ── Time ────────────────────────────────────────────────────────────────── */

el_val_t time_now(void) {
    struct timeval tv;
    gettimeofday(&tv, NULL);
    int64_t ms = (int64_t)tv.tv_sec * 1000LL + (int64_t)tv.tv_usec / 1000LL;
    return (el_val_t)ms;
}

el_val_t time_now_utc(void) {
    return time_now();
}

el_val_t time_format(el_val_t ts, el_val_t fmt) {
    int64_t ms = (int64_t)ts;
    time_t  s  = (time_t)(ms / 1000);
    int     msec = (int)(ms % 1000);
    if (msec < 0) { msec += 1000; s -= 1; }
    struct tm tm;
    gmtime_r(&s, &tm);
    const char* fmt_str = EL_CSTR(fmt);
    if (!fmt_str || *fmt_str == '\0' || strcmp(fmt_str, "ISO") == 0) {
        char buf[64];
        snprintf(buf, sizeof(buf), "%04d-%02d-%02dT%02d:%02d:%02d.%03dZ",
                 tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
                 tm.tm_hour, tm.tm_min, tm.tm_sec, msec);
        return el_wrap_str(el_strdup(buf));
    }
    char buf[256];
    if (strftime(buf, sizeof(buf), fmt_str, &tm) == 0) buf[0] = '\0';
    return el_wrap_str(el_strdup(buf));
}

el_val_t time_to_parts(el_val_t ts) {
    int64_t ms = (int64_t)ts;
    time_t  s  = (time_t)(ms / 1000);
    int     msec = (int)(ms % 1000);
    if (msec < 0) { msec += 1000; s -= 1; }
    struct tm tm;
    gmtime_r(&s, &tm);
    /* Return a JSON string so callers can use json_get to extract fields. */
    char buf[256];
    snprintf(buf, sizeof(buf),
        "{\"year\":%d,\"month\":%d,\"day\":%d,\"hour\":%d,\"minute\":%d,\"second\":%d,\"ms\":%d}",
        tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
        tm.tm_hour, tm.tm_min, tm.tm_sec, msec);
    return el_wrap_str(el_strdup(buf));
}

el_val_t time_from_parts(el_val_t secs, el_val_t ns, el_val_t tz) {
    (void)tz;
    int64_t s  = (int64_t)secs;
    int64_t n  = (int64_t)ns;
    int64_t ms = s * 1000LL + n / 1000000LL;
    return (el_val_t)ms;
}

el_val_t time_add(el_val_t ts, el_val_t n, el_val_t unit) {
    const char* u = EL_CSTR(unit);
    int64_t cur = (int64_t)ts;
    int64_t d   = (int64_t)n;
    int64_t add_ms = d;
    if (u) {
        if      (strcmp(u, "ms")   == 0) add_ms = d;
        else if (strcmp(u, "sec")  == 0) add_ms = d * 1000LL;
        else if (strcmp(u, "min")  == 0) add_ms = d * 60000LL;
        else if (strcmp(u, "hour") == 0) add_ms = d * 3600000LL;
        else if (strcmp(u, "day")  == 0) add_ms = d * 86400000LL;
    }
    return (el_val_t)(cur + add_ms);
}

el_val_t time_diff(el_val_t ts1, el_val_t ts2, el_val_t unit) {
    int64_t d = (int64_t)ts2 - (int64_t)ts1;
    const char* u = EL_CSTR(unit);
    if (!u || strcmp(u, "ms") == 0) return (el_val_t)d;
    if (strcmp(u, "sec")  == 0) return (el_val_t)(d / 1000LL);
    if (strcmp(u, "min")  == 0) return (el_val_t)(d / 60000LL);
    if (strcmp(u, "hour") == 0) return (el_val_t)(d / 3600000LL);
    if (strcmp(u, "day")  == 0) return (el_val_t)(d / 86400000LL);
    return (el_val_t)d;
}

/* Block the calling thread for `secs` seconds. Negative values are clamped
 * to 0. Used by El programs that poll external resources (e.g. RunPod
 * /status, Engram readiness probes). */
el_val_t sleep_secs(el_val_t secs) {
    int64_t s = (int64_t)secs;
    if (s < 0) s = 0;
    struct timespec ts;
    ts.tv_sec  = (time_t)s;
    ts.tv_nsec = 0;
    nanosleep(&ts, NULL);
    return 0;
}

el_val_t sleep_ms(el_val_t ms) {
    int64_t m = (int64_t)ms;
    if (m < 0) m = 0;
    struct timespec ts;
    ts.tv_sec  = (time_t)(m / 1000LL);
    ts.tv_nsec = (long)((m % 1000LL) * 1000000LL);
    nanosleep(&ts, NULL);
    return 0;
}

/* ── Instant + Duration: first-class temporal types ──────────────────────────
 * El's substrate (Neuron) is a temporal cognition system. Memory salience
 * decay, the six-tier pacemaker, TTL caches, and supersession are all
 * temporal. Treating time as a raw Int (now() returning ms-since-epoch and
 * arithmetic done with mixed unit literals) lets bugs through the type
 * system: `(now - cached_at) < 60` cannot tell ms from sec, and `sleep(30)`
 * is ambiguous. This block introduces two dedicated representations.
 *
 * Representation:
 *   Instant   — int64 nanoseconds since the Unix epoch
 *   Duration  — int64 nanoseconds (signed; negative durations are legal,
 *               e.g. when a deadline has passed)
 *
 * Both share the el_val_t (int64) slot the rest of the runtime uses, so no
 * boxing / arena allocation is needed. Type discipline is enforced at the
 * codegen layer: `let x: Duration = ...` registers `x` in __duration_names,
 * and BinOp dispatches through typed wrappers (el_duration_add, etc.) that
 * make intent explicit in the generated C. Mismatched ops (Instant+Instant,
 * Duration+Int) are surfaced via #error directives at codegen time so the
 * downstream cc step fails with a clear El-source-level message.
 *
 * Nanosecond precision matches POSIX clock_gettime / nanosleep granularity.
 * 2^63 nanos covers ~292 years from epoch — comfortably past 2200, plenty
 * for a memory-system runtime that never schedules outside a human lifespan.
 */

/* now() — current Instant. Wraps clock_gettime(CLOCK_REALTIME) for nanosecond
 * precision. Falls back to gettimeofday on systems where clock_gettime is
 * unavailable (defensive — every supported platform has it). */
el_val_t el_now_instant(void) {
    struct timespec ts;
    if (clock_gettime(CLOCK_REALTIME, &ts) == 0) {
        int64_t ns = (int64_t)ts.tv_sec * 1000000000LL + (int64_t)ts.tv_nsec;
        return (el_val_t)ns;
    }
    struct timeval tv;
    gettimeofday(&tv, NULL);
    int64_t ns = (int64_t)tv.tv_sec * 1000000000LL
               + (int64_t)tv.tv_usec * 1000LL;
    return (el_val_t)ns;
}

el_val_t now(void) {
    return el_now_instant();
}

/* now_ns — return current Unix time as nanoseconds (Int).
 * Thin wrapper over el_now_instant for use in test timing. */
el_val_t now_ns(void) {
    return el_now_instant();
}

/* unix_seconds(n)  — Instant from a Unix-epoch second count.
 * unix_millis(n)   — Instant from a Unix-epoch millisecond count.            */
el_val_t unix_seconds(el_val_t n) {
    int64_t s = (int64_t)n;
    return (el_val_t)(s * 1000000000LL);
}

el_val_t unix_millis(el_val_t n) {
    int64_t m = (int64_t)n;
    return (el_val_t)(m * 1000000LL);
}

/* instant_from_iso8601 — parse a strict subset:
 *   YYYY-MM-DDTHH:MM:SS[.fff]Z
 * Returns 0 (the Unix-epoch sentinel) on parse failure. Callers that need to
 * distinguish epoch-zero from a parse error should use a wider sentinel
 * representation; the current zero-on-failure choice matches existing El
 * runtime conventions for parse builtins (str_to_int, parse_int).            */
el_val_t instant_from_iso8601(el_val_t s) {
    const char* str = EL_CSTR(s);
    if (!str) return (el_val_t)0;
    int Y, M, D, h, m, sec, frac = 0;
    int n = sscanf(str, "%d-%d-%dT%d:%d:%d.%3d", &Y, &M, &D, &h, &m, &sec, &frac);
    if (n < 6) {
        n = sscanf(str, "%d-%d-%dT%d:%d:%dZ", &Y, &M, &D, &h, &m, &sec);
        if (n < 6) return (el_val_t)0;
    }
    struct tm tm;
    memset(&tm, 0, sizeof(tm));
    tm.tm_year = Y - 1900;
    tm.tm_mon  = M - 1;
    tm.tm_mday = D;
    tm.tm_hour = h;
    tm.tm_min  = m;
    tm.tm_sec  = sec;
    /* timegm — UTC. POSIX-Y but available on macOS and glibc. */
    time_t t = timegm(&tm);
    if (t == (time_t)-1) return (el_val_t)0;
    int64_t ns = (int64_t)t * 1000000000LL + (int64_t)frac * 1000000LL;
    return (el_val_t)ns;
}

/* Duration constructors. The El-side postfix literals (30.seconds, 1.hour)
 * are lowered by the codegen directly into a literal int64 of nanoseconds —
 * these constructors are for runtime values where the count is dynamic. */
el_val_t el_duration_from_nanos(el_val_t ns) {
    return (el_val_t)(int64_t)ns;
}

el_val_t duration_seconds(el_val_t n) {
    int64_t s = (int64_t)n;
    return (el_val_t)(s * 1000000000LL);
}

el_val_t duration_millis(el_val_t n) {
    int64_t m = (int64_t)n;
    return (el_val_t)(m * 1000000LL);
}

el_val_t duration_nanos(el_val_t n) {
    return (el_val_t)(int64_t)n;
}

/* Arithmetic — typed wrappers. At the C level these are no-op casts, but
 * the codegen routes Instant/Duration BinOps through them so the generated
 * C says `el_instant_add_dur(start, dur)` rather than `start + dur`. The
 * intent is explicit, the operand order is documented, and a future change
 * to the underlying representation (saturating arithmetic, overflow guards)
 * has a single chokepoint.                                                  */
el_val_t el_instant_add_dur(el_val_t inst, el_val_t dur) {
    return (el_val_t)((int64_t)inst + (int64_t)dur);
}

el_val_t el_instant_sub_dur(el_val_t inst, el_val_t dur) {
    return (el_val_t)((int64_t)inst - (int64_t)dur);
}

el_val_t el_instant_diff(el_val_t a, el_val_t b) {
    /* a - b — yields a Duration (negative if b is later than a). */
    return (el_val_t)((int64_t)a - (int64_t)b);
}

el_val_t el_duration_add(el_val_t a, el_val_t b) {
    return (el_val_t)((int64_t)a + (int64_t)b);
}

el_val_t el_duration_sub(el_val_t a, el_val_t b) {
    return (el_val_t)((int64_t)a - (int64_t)b);
}

el_val_t el_duration_scale(el_val_t dur, el_val_t scalar) {
    return (el_val_t)((int64_t)dur * (int64_t)scalar);
}

el_val_t el_duration_div(el_val_t dur, el_val_t scalar) {
    int64_t s = (int64_t)scalar;
    if (s == 0) return (el_val_t)0;
    return (el_val_t)((int64_t)dur / s);
}

/* Comparisons. Return 1/0 in el_val_t convention. */
el_val_t el_instant_lt(el_val_t a, el_val_t b)  { return (el_val_t)((int64_t)a <  (int64_t)b ? 1 : 0); }
el_val_t el_instant_le(el_val_t a, el_val_t b)  { return (el_val_t)((int64_t)a <= (int64_t)b ? 1 : 0); }
el_val_t el_instant_gt(el_val_t a, el_val_t b)  { return (el_val_t)((int64_t)a >  (int64_t)b ? 1 : 0); }
el_val_t el_instant_ge(el_val_t a, el_val_t b)  { return (el_val_t)((int64_t)a >= (int64_t)b ? 1 : 0); }
el_val_t el_instant_eq(el_val_t a, el_val_t b)  { return (el_val_t)((int64_t)a == (int64_t)b ? 1 : 0); }
el_val_t el_instant_ne(el_val_t a, el_val_t b)  { return (el_val_t)((int64_t)a != (int64_t)b ? 1 : 0); }
el_val_t el_duration_lt(el_val_t a, el_val_t b) { return (el_val_t)((int64_t)a <  (int64_t)b ? 1 : 0); }
el_val_t el_duration_le(el_val_t a, el_val_t b) { return (el_val_t)((int64_t)a <= (int64_t)b ? 1 : 0); }
el_val_t el_duration_gt(el_val_t a, el_val_t b) { return (el_val_t)((int64_t)a >  (int64_t)b ? 1 : 0); }
el_val_t el_duration_ge(el_val_t a, el_val_t b) { return (el_val_t)((int64_t)a >= (int64_t)b ? 1 : 0); }
el_val_t el_duration_eq(el_val_t a, el_val_t b) { return (el_val_t)((int64_t)a == (int64_t)b ? 1 : 0); }
el_val_t el_duration_ne(el_val_t a, el_val_t b) { return (el_val_t)((int64_t)a != (int64_t)b ? 1 : 0); }

/* Conversions. */
el_val_t instant_to_unix_seconds(el_val_t i) {
    return (el_val_t)((int64_t)i / 1000000000LL);
}

el_val_t instant_to_unix_millis(el_val_t i) {
    return (el_val_t)((int64_t)i / 1000000LL);
}

el_val_t instant_to_iso8601(el_val_t i) {
    int64_t ns = (int64_t)i;
    time_t s = (time_t)(ns / 1000000000LL);
    int    msec = (int)((ns / 1000000LL) % 1000LL);
    if (msec < 0) { msec += 1000; s -= 1; }
    struct tm tm;
    gmtime_r(&s, &tm);
    char buf[64];
    snprintf(buf, sizeof(buf), "%04d-%02d-%02dT%02d:%02d:%02d.%03dZ",
             tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
             tm.tm_hour, tm.tm_min, tm.tm_sec, msec);
    return el_wrap_str(el_strdup(buf));
}

el_val_t duration_to_seconds(el_val_t d) {
    return (el_val_t)((int64_t)d / 1000000000LL);
}

el_val_t duration_to_millis(el_val_t d) {
    return (el_val_t)((int64_t)d / 1000000LL);
}

el_val_t duration_to_nanos(el_val_t d) {
    return (el_val_t)(int64_t)d;
}

/* sleep(Duration) — Phase 1 replacement for ambiguous sleep(Int). The runtime
 * still exposes sleep_secs/sleep_ms for legacy call sites; codegen lowers
 * sleep(Duration) to el_sleep_duration(d). Negative durations clamp to 0 so a
 * stale deadline doesn't block forever. */
el_val_t el_sleep_duration(el_val_t dur) {
    int64_t ns = (int64_t)dur;
    if (ns < 0) ns = 0;
    struct timespec ts;
    ts.tv_sec  = (time_t)(ns / 1000000000LL);
    ts.tv_nsec = (long)(ns % 1000000000LL);
    nanosleep(&ts, NULL);
    return (el_val_t)0;
}

/* unix_timestamp() — back-compat. Existing El callers expect an Int seconds
 * value; this stays an Int returner so the type system isn't disturbed for
 * legacy code. New code should call now() and convert when needed.          */
el_val_t unix_timestamp(void) {
    return instant_to_unix_seconds(el_now_instant());
}

/* TTL cache helpers. Backed by the existing process-wide K/V (state_set/get)
 * with a sibling __ttl_set_at_<key> entry recording the Instant of the last
 * write. ttl_cache_get returns "" if the entry is missing or stale, so call
 * sites can branch on `if v == "" { miss } else { hit }` — the same shape
 * existing get-with-default code uses. No more (now - cached_at) < 60. */
el_val_t ttl_cache_set(el_val_t key, el_val_t value) {
    const char* k = EL_CSTR(key);
    if (!k) return (el_val_t)0;
    /* Store the value at the user's key. */
    state_set(key, value);
    /* Stamp set_at — opaque schema, namespaced under __ttl: prefix so user
     * keys can't collide with stamps. */
    size_t klen = strlen(k);
    char* stamp_key = (char*)malloc(klen + 16);
    if (!stamp_key) return (el_val_t)0;
    snprintf(stamp_key, klen + 16, "__ttl_at:%s", k);
    int64_t now_ns = (int64_t)el_now_instant();
    char buf[32];
    snprintf(buf, sizeof(buf), "%lld", (long long)now_ns);
    state_set(EL_STR(stamp_key), EL_STR(buf));
    free(stamp_key);
    return (el_val_t)1;
}

el_val_t ttl_cache_get(el_val_t key, el_val_t max_age) {
    const char* k = EL_CSTR(key);
    if (!k) return el_wrap_str(el_strdup(""));
    /* Look up stamp. */
    size_t klen = strlen(k);
    char* stamp_key = (char*)malloc(klen + 16);
    if (!stamp_key) return el_wrap_str(el_strdup(""));
    snprintf(stamp_key, klen + 16, "__ttl_at:%s", k);
    el_val_t stamp = state_get(EL_STR(stamp_key));
    free(stamp_key);
    const char* sv = EL_CSTR(stamp);
    if (!sv || !*sv) return el_wrap_str(el_strdup(""));
    int64_t set_at = (int64_t)atoll(sv);
    int64_t now_ns = (int64_t)el_now_instant();
    int64_t age    = now_ns - set_at;
    int64_t max_ns = (int64_t)max_age;
    if (age < 0)       return el_wrap_str(el_strdup(""));   /* clock skew — treat as miss */
    if (age > max_ns)  return el_wrap_str(el_strdup(""));   /* expired */
    return state_get(key);
}

el_val_t ttl_cache_age(el_val_t key) {
    const char* k = EL_CSTR(key);
    if (!k) return (el_val_t)INT64_MAX;
    size_t klen = strlen(k);
    char* stamp_key = (char*)malloc(klen + 16);
    if (!stamp_key) return (el_val_t)INT64_MAX;
    snprintf(stamp_key, klen + 16, "__ttl_at:%s", k);
    el_val_t stamp = state_get(EL_STR(stamp_key));
    free(stamp_key);
    const char* sv = EL_CSTR(stamp);
    if (!sv || !*sv) return (el_val_t)INT64_MAX;
    int64_t set_at = (int64_t)atoll(sv);
    int64_t now_ns = (int64_t)el_now_instant();
    return (el_val_t)(now_ns - set_at);
}

/* ── Calendar + CalendarTime + Rhythm + LocalDate/Time/DateTime ──────────────
 * Phase 1.5. Calendar is pluggable: EarthCalendar (IANA zones + Gregorian +
 * DST), MarsCalendar (sols, MTC), CycleCalendar(period), NoCycleCalendar,
 * RelativeCalendar(epoch). Phase 1 zone wrapping folds INTO EarthCalendar;
 * UTC and IANA zones are themselves Earth-parochial and cannot live at the
 * lowest type layer.
 *
 * A Rhythm is a small AST that asks the Calendar for cycle phase, weekday,
 * etc. Most rhythm logic is calendar-agnostic at runtime: rhythm_cycle_phase
 * means "midpoint of cycle" whether the cycle is 24h on Earth or 30h on a
 * station or 300y on a long-cycle world.                                     */

/* Magic headers — used by the runtime to recognize boxed temporal values
 * arriving through el_val_t. Distinct constants so accidental misuse fails
 * loudly rather than silently.                                              */
#define EL_CAL_MAGIC      0xE1CA1EDDU
#define EL_CALTIME_MAGIC  0xE1CA1747U
#define EL_RHYTHM_MAGIC   0xE1287A11U
#define EL_LDATE_MAGIC    0xE1DA7E00U
#define EL_LDT_MAGIC      0xE1DA7E1DU
#define EL_ZONE_MAGIC     0xE12017E0U

typedef enum {
    EL_CALENDAR_EARTH    = 1,
    EL_CALENDAR_MARS     = 2,
    EL_CALENDAR_CYCLE    = 3,
    EL_CALENDAR_NO_CYCLE = 4,
    EL_CALENDAR_RELATIVE = 5
} el_calendar_kind_t;

typedef struct {
    uint32_t magic;
    char*    id;        /* IANA name or "+HH:MM" / "-HH:MM" */
    int      fixed;     /* 1 for fixed offset, 0 for IANA */
    int64_t  offset_ns; /* fixed offset in nanos (only when fixed) */
} el_zone_t;

typedef struct {
    uint32_t            magic;
    el_calendar_kind_t  kind;
    el_zone_t*          zone;          /* EarthCalendar; MarsCalendar uses MTC */
    int64_t             cycle_period_ns;/* CycleCalendar; computed for Earth (86400 s) and Mars (88775.244 s) */
    int64_t             epoch_ns;      /* RelativeCalendar; Unix-epoch zero otherwise */
} el_calendar_t;

typedef struct {
    uint32_t        magic;
    int64_t         instant_ns;
    el_calendar_t*  cal;
} el_caltime_t;

/* Rhythm AST. */
typedef enum {
    EL_RHYTHM_CYCLE_START   = 1,
    EL_RHYTHM_CYCLE_PHASE   = 2,
    EL_RHYTHM_DURATION      = 3,
    EL_RHYTHM_SESSION_START = 4,
    EL_RHYTHM_EVENT         = 5,
    EL_RHYTHM_AND           = 6,
    EL_RHYTHM_OR            = 7,
    EL_RHYTHM_WEEKDAY       = 8,
    EL_RHYTHM_WEEKLY_AT     = 9
} el_rhythm_kind_t;

typedef struct el_rhythm_s {
    uint32_t            magic;
    el_rhythm_kind_t    kind;
    double              phase;       /* CYCLE_PHASE */
    int64_t             period_ns;   /* DURATION */
    int                 weekday;     /* 1..7 Mon..Sun */
    int                 hour;
    int                 minute;
    char*               event_name;  /* EVENT */
    struct el_rhythm_s* a;           /* AND/OR */
    struct el_rhythm_s* b;
} el_rhythm_t;

typedef struct {
    uint32_t magic;
    int      year;
    int      month;
    int      day;
} el_localdate_t;

typedef struct {
    uint32_t        magic;
    el_localdate_t* date;
    int64_t         time_ns; /* nanos since midnight */
} el_localdt_t;

/* Magic-tag check helpers — peek the first 4 bytes of an el_val_t pointer
 * and compare against the expected magic. Strings are NUL-terminated and
 * never start with our magic byte sequence, so this is safe.               */
static int el_is_magic(el_val_t v, uint32_t want) {
    if (v == 0) return 0;
    /* Defensive: only follow pointers in plausible address space.
     * On 64-bit unix processes pointers are above 0x10000. */
    if ((uint64_t)v < 0x10000ULL) return 0;
    uint32_t got = *(volatile uint32_t*)(uintptr_t)v;
    return got == want;
}

/* Sol length on Mars in nanoseconds: 88775.244 seconds. */
#define EL_MARS_SOL_NS  ((int64_t)88775244000000LL)
/* Earth solar day in nanoseconds: 86400 seconds. */
#define EL_EARTH_DAY_NS ((int64_t)86400000000000LL)

/* ── Zone construction ──────────────────────────────────────────────────────
 * Zones intern by id string so equality comparisons are pointer-compares. */

#define EL_ZONE_TABLE_CAP 64
static el_zone_t* _el_zone_table[EL_ZONE_TABLE_CAP];
static int        _el_zone_count = 0;

static el_zone_t* _el_zone_intern(const char* id, int fixed, int64_t offset_ns) {
    for (int i = 0; i < _el_zone_count; i++) {
        el_zone_t* z = _el_zone_table[i];
        if (z->fixed == fixed && z->offset_ns == offset_ns &&
            strcmp(z->id ? z->id : "", id ? id : "") == 0) {
            return z;
        }
    }
    if (_el_zone_count >= EL_ZONE_TABLE_CAP) {
        /* Out of slots: build a non-interned zone. Equality will fail across
         * such zones but the program still runs. */
        el_zone_t* z = (el_zone_t*)malloc(sizeof(el_zone_t));
        z->magic = EL_ZONE_MAGIC;
        z->id = el_strdup_persist(id ? id : "");
        z->fixed = fixed;
        z->offset_ns = offset_ns;
        return z;
    }
    el_zone_t* z = (el_zone_t*)malloc(sizeof(el_zone_t));
    z->magic = EL_ZONE_MAGIC;
    z->id = el_strdup_persist(id ? id : "");
    z->fixed = fixed;
    z->offset_ns = offset_ns;
    _el_zone_table[_el_zone_count++] = z;
    return z;
}

el_val_t zone(el_val_t id) {
    const char* s = EL_CSTR(id);
    if (!s || !*s) return (el_val_t)(uintptr_t)_el_zone_intern("UTC", 0, 0);
    /* Fixed-offset shortcut: "+HH:MM" or "-HH:MM". */
    if ((s[0] == '+' || s[0] == '-') && strlen(s) >= 6 && s[3] == ':') {
        int sign = (s[0] == '-') ? -1 : 1;
        int hh = (s[1] - '0') * 10 + (s[2] - '0');
        int mm = (s[4] - '0') * 10 + (s[5] - '0');
        int64_t off = (int64_t)sign * ((int64_t)hh * 3600LL + (int64_t)mm * 60LL) * 1000000000LL;
        return (el_val_t)(uintptr_t)_el_zone_intern(s, 1, off);
    }
    return (el_val_t)(uintptr_t)_el_zone_intern(s, 0, 0);
}

el_val_t zone_utc(void) {
    return (el_val_t)(uintptr_t)_el_zone_intern("UTC", 1, 0);
}

el_val_t zone_local(void) {
    /* Resolve the local zone via TZ env or system default. tzset() picks
     * up TZ if set; otherwise the C library reads /etc/localtime. We store
     * the zone id as "LOCAL" so subsequent equality holds; resolution is
     * lazy at use time. */
    return (el_val_t)(uintptr_t)_el_zone_intern("LOCAL", 0, 0);
}

el_val_t zone_offset(el_val_t hours, el_val_t minutes) {
    int hh = (int)(int64_t)hours;
    int mm = (int)(int64_t)minutes;
    int sign = (hh < 0 || mm < 0) ? -1 : 1;
    if (hh < 0) hh = -hh;
    if (mm < 0) mm = -mm;
    int64_t off = (int64_t)sign * ((int64_t)hh * 3600LL + (int64_t)mm * 60LL) * 1000000000LL;
    char buf[16];
    snprintf(buf, sizeof(buf), "%c%02d:%02d", sign < 0 ? '-' : '+', hh, mm);
    return (el_val_t)(uintptr_t)_el_zone_intern(buf, 1, off);
}

/* ── Calendar interning ──────────────────────────────────────────────────── */

#define EL_CAL_TABLE_CAP 64
static el_calendar_t* _el_cal_table[EL_CAL_TABLE_CAP];
static int            _el_cal_count = 0;

static el_calendar_t* _el_cal_intern(el_calendar_kind_t kind, el_zone_t* z,
                                     int64_t period_ns, int64_t epoch_ns) {
    for (int i = 0; i < _el_cal_count; i++) {
        el_calendar_t* c = _el_cal_table[i];
        if (c->kind == kind && c->zone == z &&
            c->cycle_period_ns == period_ns && c->epoch_ns == epoch_ns) {
            return c;
        }
    }
    el_calendar_t* c = (el_calendar_t*)malloc(sizeof(el_calendar_t));
    c->magic = EL_CAL_MAGIC;
    c->kind = kind;
    c->zone = z;
    c->cycle_period_ns = period_ns;
    c->epoch_ns = epoch_ns;
    if (_el_cal_count < EL_CAL_TABLE_CAP) _el_cal_table[_el_cal_count++] = c;
    return c;
}

el_val_t earth_calendar(el_val_t z_val) {
    el_zone_t* z = NULL;
    if (z_val != 0 && el_is_magic(z_val, EL_ZONE_MAGIC)) {
        z = (el_zone_t*)(uintptr_t)z_val;
    } else {
        z = (el_zone_t*)(uintptr_t)zone_local();
    }
    return (el_val_t)(uintptr_t)_el_cal_intern(EL_CALENDAR_EARTH, z, EL_EARTH_DAY_NS, 0);
}

el_val_t earth_calendar_default(void) {
    return earth_calendar(zone_local());
}

el_val_t mars_calendar(void) {
    el_zone_t* z = (el_zone_t*)(uintptr_t)_el_zone_intern("MTC", 1, 0);
    return (el_val_t)(uintptr_t)_el_cal_intern(EL_CALENDAR_MARS, z, EL_MARS_SOL_NS, 0);
}

el_val_t cycle_calendar(el_val_t period_dur) {
    int64_t period = (int64_t)period_dur;
    if (period <= 0) period = 1;
    return (el_val_t)(uintptr_t)_el_cal_intern(EL_CALENDAR_CYCLE, NULL, period, 0);
}

el_val_t no_cycle_calendar(void) {
    return (el_val_t)(uintptr_t)_el_cal_intern(EL_CALENDAR_NO_CYCLE, NULL, 0, 0);
}

el_val_t relative_calendar(el_val_t epoch_inst) {
    int64_t ep = (int64_t)epoch_inst;
    return (el_val_t)(uintptr_t)_el_cal_intern(EL_CALENDAR_RELATIVE, NULL, 0, ep);
}

/* ── CalendarTime ───────────────────────────────────────────────────────── */

static el_caltime_t* _el_caltime_alloc(int64_t inst, el_calendar_t* c) {
    el_caltime_t* ct = (el_caltime_t*)malloc(sizeof(el_caltime_t));
    ct->magic = EL_CALTIME_MAGIC;
    ct->instant_ns = inst;
    ct->cal = c;
    return ct;
}

static el_calendar_t* _el_resolve_cal(el_val_t cal_val) {
    if (cal_val == 0 || !el_is_magic(cal_val, EL_CAL_MAGIC)) {
        return (el_calendar_t*)(uintptr_t)earth_calendar_default();
    }
    return (el_calendar_t*)(uintptr_t)cal_val;
}

el_val_t now_in(el_val_t cal_val) {
    el_calendar_t* c = _el_resolve_cal(cal_val);
    int64_t ns = (int64_t)el_now_instant();
    return (el_val_t)(uintptr_t)_el_caltime_alloc(ns, c);
}

el_val_t in_calendar(el_val_t inst, el_val_t cal_val) {
    el_calendar_t* c = _el_resolve_cal(cal_val);
    return (el_val_t)(uintptr_t)_el_caltime_alloc((int64_t)inst, c);
}

el_val_t cal_to_instant(el_val_t ct_val) {
    if (!el_is_magic(ct_val, EL_CALTIME_MAGIC)) return (el_val_t)0;
    el_caltime_t* ct = (el_caltime_t*)(uintptr_t)ct_val;
    return (el_val_t)ct->instant_ns;
}

el_val_t cal_in(el_val_t ct_val, el_val_t cal_val) {
    if (!el_is_magic(ct_val, EL_CALTIME_MAGIC)) return (el_val_t)0;
    el_caltime_t* ct = (el_caltime_t*)(uintptr_t)ct_val;
    el_calendar_t* c = _el_resolve_cal(cal_val);
    return (el_val_t)(uintptr_t)_el_caltime_alloc(ct->instant_ns, c);
}

el_val_t cal_cycle_phase(el_val_t ct_val) {
    if (!el_is_magic(ct_val, EL_CALTIME_MAGIC)) return el_from_float(0.0);
    el_caltime_t* ct = (el_caltime_t*)(uintptr_t)ct_val;
    el_calendar_t* c = ct->cal;
    if (c->kind == EL_CALENDAR_NO_CYCLE) {
        return el_from_float(0.0/0.0); /* NaN sentinel */
    }
    int64_t period = c->cycle_period_ns;
    if (period <= 0) return el_from_float(0.0);
    int64_t base = ct->instant_ns - c->epoch_ns;
    int64_t phase_ns = base % period;
    if (phase_ns < 0) phase_ns += period;
    double phase = (double)phase_ns / (double)period;
    return el_from_float(phase);
}

/* ── Earth zone resolution: TZ-based offset lookup ──────────────────────────
 * For an EarthCalendar(zone), we want to convert an instant_ns into local
 * y/m/d/h/m/s, including DST. Approach: setenv("TZ", id), tzset(), use
 * localtime_r, then restore. This is not thread-safe by design — El's
 * runtime is single-threaded for the request handler path. Cache the
 * computed (instant -> tm) to avoid the syscall churn on repeat formats. */

static void _el_apply_zone(el_zone_t* z) {
    if (!z) { unsetenv("TZ"); tzset(); return; }
    if (z->fixed && strcmp(z->id, "UTC") == 0) {
        setenv("TZ", "UTC0", 1);
        tzset();
        return;
    }
    if (z->fixed) {
        /* Fixed offset: POSIX TZ uses inverted sign (sign convention of
         * "hours WEST of UTC" rather than east). Build the spec accordingly. */
        char buf[32];
        int neg_secs = (int)(-z->offset_ns / 1000000000LL);
        int sign = neg_secs < 0 ? -1 : 1;
        int abs_secs = neg_secs < 0 ? -neg_secs : neg_secs;
        int hh = abs_secs / 3600;
        int mm = (abs_secs % 3600) / 60;
        snprintf(buf, sizeof(buf), "FIX%c%d:%02d", sign < 0 ? '-' : '+', hh, mm);
        setenv("TZ", buf, 1);
        tzset();
        return;
    }
    if (strcmp(z->id, "LOCAL") == 0) {
        unsetenv("TZ");
        tzset();
        return;
    }
    setenv("TZ", z->id, 1);
    tzset();
}

static int _el_decompose_earth(el_caltime_t* ct, struct tm* tm_out, int* abbr_len, char* abbr_buf, size_t abbr_cap) {
    el_calendar_t* c = ct->cal;
    el_zone_t* z = c->zone;
    _el_apply_zone(z);
    time_t s = (time_t)(ct->instant_ns / 1000000000LL);
    struct tm tm;
    localtime_r(&s, &tm);
    *tm_out = tm;
    if (abbr_buf && abbr_cap > 0) {
        const char* z_str = tm.tm_zone ? tm.tm_zone : "";
        size_t n = strlen(z_str);
        if (n >= abbr_cap) n = abbr_cap - 1;
        memcpy(abbr_buf, z_str, n);
        abbr_buf[n] = '\0';
        if (abbr_len) *abbr_len = (int)n;
    }
    return 0;
}

/* Format an Earth CalendarTime under a Java-DateTimeFormatter-ish pattern.
 * We support a useful core: yyyy MM dd HH mm ss z EEE MMM d h a — enough for
 * the acceptance tests. Single quotes denote literal text. */
static const char* _el_weekday_short[] = {"Sun","Mon","Tue","Wed","Thu","Fri","Sat"};
static const char* _el_month_short[]   = {"Jan","Feb","Mar","Apr","May","Jun",
                                          "Jul","Aug","Sep","Oct","Nov","Dec"};

static char* _el_format_earth(el_caltime_t* ct, const char* pattern) {
    struct tm tm;
    char abbr[16] = {0};
    int abbr_len = 0;
    _el_decompose_earth(ct, &tm, &abbr_len, abbr, sizeof(abbr));
    size_t cap = strlen(pattern) * 4 + 64;
    char* out = (char*)malloc(cap);
    size_t pos = 0;
    size_t i = 0;
    size_t plen = strlen(pattern);
    while (i < plen) {
        char ch = pattern[i];
        /* Quoted literal */
        if (ch == '\'') {
            i++;
            while (i < plen && pattern[i] != '\'') {
                if (pos + 1 >= cap) { cap *= 2; out = realloc(out, cap); }
                out[pos++] = pattern[i++];
            }
            if (i < plen) i++;
            continue;
        }
        /* Count run of same letter */
        size_t run = 1;
        while (i + run < plen && pattern[i + run] == ch) run++;
        char tmp[64];
        tmp[0] = '\0';
        if (ch == 'y') {
            if (run >= 4) snprintf(tmp, sizeof(tmp), "%04d", tm.tm_year + 1900);
            else snprintf(tmp, sizeof(tmp), "%02d", (tm.tm_year + 1900) % 100);
        } else if (ch == 'M') {
            if (run >= 3) snprintf(tmp, sizeof(tmp), "%s", _el_month_short[tm.tm_mon]);
            else if (run == 2) snprintf(tmp, sizeof(tmp), "%02d", tm.tm_mon + 1);
            else snprintf(tmp, sizeof(tmp), "%d", tm.tm_mon + 1);
        } else if (ch == 'd') {
            if (run >= 2) snprintf(tmp, sizeof(tmp), "%02d", tm.tm_mday);
            else snprintf(tmp, sizeof(tmp), "%d", tm.tm_mday);
        } else if (ch == 'H') {
            if (run >= 2) snprintf(tmp, sizeof(tmp), "%02d", tm.tm_hour);
            else snprintf(tmp, sizeof(tmp), "%d", tm.tm_hour);
        } else if (ch == 'h') {
            int h12 = tm.tm_hour % 12; if (h12 == 0) h12 = 12;
            if (run >= 2) snprintf(tmp, sizeof(tmp), "%02d", h12);
            else snprintf(tmp, sizeof(tmp), "%d", h12);
        } else if (ch == 'm') {
            if (run >= 2) snprintf(tmp, sizeof(tmp), "%02d", tm.tm_min);
            else snprintf(tmp, sizeof(tmp), "%d", tm.tm_min);
        } else if (ch == 's') {
            if (run >= 2) snprintf(tmp, sizeof(tmp), "%02d", tm.tm_sec);
            else snprintf(tmp, sizeof(tmp), "%d", tm.tm_sec);
        } else if (ch == 'a') {
            snprintf(tmp, sizeof(tmp), "%s", tm.tm_hour < 12 ? "AM" : "PM");
        } else if (ch == 'E') {
            snprintf(tmp, sizeof(tmp), "%s", _el_weekday_short[tm.tm_wday]);
        } else if (ch == 'z') {
            snprintf(tmp, sizeof(tmp), "%s", abbr);
        } else {
            for (size_t k = 0; k < run; k++) {
                if (pos + 1 >= cap) { cap *= 2; out = realloc(out, cap); }
                out[pos++] = ch;
            }
            i += run;
            continue;
        }
        size_t tl = strlen(tmp);
        if (pos + tl + 1 >= cap) { cap = (cap + tl) * 2; out = realloc(out, cap); }
        memcpy(out + pos, tmp, tl);
        pos += tl;
        i += run;
    }
    out[pos] = '\0';
    char* result = el_strdup(out);
    free(out);
    return result;
}

/* Format a Mars CalendarTime: %sol prints the integer sol number since
 * mission epoch (Unix epoch fallback), %phase prints cycle_phase as a
 * 0..1 decimal. Other %-specifiers fall through. */
static char* _el_format_mars(el_caltime_t* ct, const char* pattern) {
    el_calendar_t* c = ct->cal;
    int64_t period = c->cycle_period_ns > 0 ? c->cycle_period_ns : EL_MARS_SOL_NS;
    int64_t base = ct->instant_ns - c->epoch_ns;
    int64_t sol = base / period;
    int64_t phase_ns = base % period;
    if (phase_ns < 0) { phase_ns += period; sol -= 1; }
    double phase = (double)phase_ns / (double)period;
    size_t cap = strlen(pattern) * 4 + 64;
    char* out = (char*)malloc(cap);
    size_t pos = 0;
    for (size_t i = 0; pattern[i]; i++) {
        if (pattern[i] == '%' && pattern[i+1]) {
            char tmp[64];
            tmp[0] = '\0';
            if (strncmp(pattern + i + 1, "sol", 3) == 0) {
                snprintf(tmp, sizeof(tmp), "%lld", (long long)sol);
                i += 3;
            } else if (strncmp(pattern + i + 1, "phase", 5) == 0) {
                snprintf(tmp, sizeof(tmp), "%.4f", phase);
                i += 5;
            } else if (pattern[i+1] == 'd') {
                snprintf(tmp, sizeof(tmp), "%lld", (long long)sol);
                i += 1;
            } else {
                tmp[0] = pattern[i+1]; tmp[1] = '\0';
                i += 1;
            }
            size_t tl = strlen(tmp);
            if (pos + tl + 1 >= cap) { cap = (cap + tl) * 2; out = realloc(out, cap); }
            memcpy(out + pos, tmp, tl);
            pos += tl;
        } else {
            if (pos + 1 >= cap) { cap *= 2; out = realloc(out, cap); }
            out[pos++] = pattern[i];
        }
    }
    out[pos] = '\0';
    char* result = el_strdup(out);
    free(out);
    return result;
}

/* Format a CycleCalendar CalendarTime: %cycle and %phase. */
static char* _el_format_cycle(el_caltime_t* ct, const char* pattern) {
    el_calendar_t* c = ct->cal;
    int64_t period = c->cycle_period_ns > 0 ? c->cycle_period_ns : 1;
    int64_t base = ct->instant_ns - c->epoch_ns;
    int64_t cycle = base / period;
    int64_t phase_ns = base % period;
    if (phase_ns < 0) { phase_ns += period; cycle -= 1; }
    double phase = (double)phase_ns / (double)period;
    size_t cap = strlen(pattern) * 4 + 64;
    char* out = (char*)malloc(cap);
    size_t pos = 0;
    for (size_t i = 0; pattern[i]; i++) {
        if (pattern[i] == '%' && pattern[i+1]) {
            char tmp[64];
            tmp[0] = '\0';
            if (strncmp(pattern + i + 1, "cycle", 5) == 0) {
                snprintf(tmp, sizeof(tmp), "%lld", (long long)cycle);
                i += 5;
            } else if (strncmp(pattern + i + 1, "phase", 5) == 0) {
                snprintf(tmp, sizeof(tmp), "%.4f", phase);
                i += 5;
            } else if (pattern[i+1] == 'd') {
                snprintf(tmp, sizeof(tmp), "%lld", (long long)cycle);
                i += 1;
            } else if (pattern[i+1] == 'f') {
                snprintf(tmp, sizeof(tmp), "%.2f", phase);
                i += 1;
            } else {
                /* Pass through unknown specifier */
                tmp[0] = '%'; tmp[1] = pattern[i+1]; tmp[2] = '\0';
                i += 1;
            }
            size_t tl = strlen(tmp);
            if (pos + tl + 1 >= cap) { cap = (cap + tl) * 2; out = realloc(out, cap); }
            memcpy(out + pos, tmp, tl);
            pos += tl;
        } else {
            if (pos + 1 >= cap) { cap *= 2; out = realloc(out, cap); }
            out[pos++] = pattern[i];
        }
    }
    out[pos] = '\0';
    char* result = el_strdup(out);
    free(out);
    return result;
}

el_val_t cal_format(el_val_t ct_val, el_val_t pattern_val) {
    if (!el_is_magic(ct_val, EL_CALTIME_MAGIC)) return el_wrap_str(el_strdup(""));
    el_caltime_t* ct = (el_caltime_t*)(uintptr_t)ct_val;
    const char* pat = EL_CSTR(pattern_val);
    if (!pat) pat = "";
    char* result = NULL;
    switch (ct->cal->kind) {
        case EL_CALENDAR_EARTH:    result = _el_format_earth(ct, pat); break;
        case EL_CALENDAR_MARS:     result = _el_format_mars(ct, pat);  break;
        case EL_CALENDAR_CYCLE:    result = _el_format_cycle(ct, pat); break;
        case EL_CALENDAR_RELATIVE: result = _el_format_cycle(ct, pat); break;
        case EL_CALENDAR_NO_CYCLE: {
            char buf[64];
            snprintf(buf, sizeof(buf), "instant:%lld", (long long)ct->instant_ns);
            result = el_strdup(buf);
            break;
        }
        default: result = el_strdup("");
    }
    return el_wrap_str(result);
}

/* ── LocalDate / LocalTime / LocalDateTime ──────────────────────────────── */

static int _el_days_in_month(int y, int m) {
    static const int dim[12] = {31,28,31,30,31,30,31,31,30,31,30,31};
    if (m == 2) {
        int leap = ((y % 4 == 0) && (y % 100 != 0)) || (y % 400 == 0);
        return 28 + (leap ? 1 : 0);
    }
    if (m < 1 || m > 12) return 30;
    return dim[m - 1];
}

el_val_t local_date(el_val_t y, el_val_t m, el_val_t d) {
    el_localdate_t* ld = (el_localdate_t*)malloc(sizeof(el_localdate_t));
    ld->magic = EL_LDATE_MAGIC;
    ld->year = (int)(int64_t)y;
    ld->month = (int)(int64_t)m;
    ld->day = (int)(int64_t)d;
    return (el_val_t)(uintptr_t)ld;
}

el_val_t local_time(el_val_t h, el_val_t m, el_val_t s, el_val_t ns) {
    int64_t hh = (int64_t)h;
    int64_t mm = (int64_t)m;
    int64_t ss = (int64_t)s;
    int64_t nn = (int64_t)ns;
    int64_t total = hh * 3600000000000LL + mm * 60000000000LL + ss * 1000000000LL + nn;
    return (el_val_t)total;
}

el_val_t local_datetime(el_val_t date_val, el_val_t time_val) {
    if (!el_is_magic(date_val, EL_LDATE_MAGIC)) return (el_val_t)0;
    el_localdt_t* ldt = (el_localdt_t*)malloc(sizeof(el_localdt_t));
    ldt->magic = EL_LDT_MAGIC;
    ldt->date = (el_localdate_t*)(uintptr_t)date_val;
    ldt->time_ns = (int64_t)time_val;
    return (el_val_t)(uintptr_t)ldt;
}

el_val_t zoned(el_val_t date_val, el_val_t time_val, el_val_t cal_val) {
    if (!el_is_magic(date_val, EL_LDATE_MAGIC)) return (el_val_t)0;
    el_localdate_t* ld = (el_localdate_t*)(uintptr_t)date_val;
    el_calendar_t* c = _el_resolve_cal(cal_val);
    int64_t time_ns = (int64_t)time_val;
    /* Convert (LocalDate, LocalTime, EarthCalendar) -> Instant.
     * For non-Earth calendars we use day-anchored conversion: treat the
     * LocalDate's (y,m,d) as a Gregorian projection, convert to seconds via
     * mktime under the calendar's zone, then add nanos-since-midnight. */
    if (c->kind == EL_CALENDAR_EARTH) {
        _el_apply_zone(c->zone);
        struct tm tm; memset(&tm, 0, sizeof(tm));
        tm.tm_year = ld->year - 1900;
        tm.tm_mon  = ld->month - 1;
        tm.tm_mday = ld->day;
        tm.tm_hour = (int)(time_ns / 3600000000000LL);
        tm.tm_min  = (int)((time_ns / 60000000000LL) % 60);
        tm.tm_sec  = (int)((time_ns / 1000000000LL) % 60);
        tm.tm_isdst = -1;
        time_t t = mktime(&tm);
        if (t == (time_t)-1) return (el_val_t)0;
        int64_t ns = (int64_t)t * 1000000000LL + (time_ns % 1000000000LL);
        return (el_val_t)(uintptr_t)_el_caltime_alloc(ns, c);
    }
    /* Non-Earth fallback: project as if Earth UTC then attach calendar. */
    struct tm tm; memset(&tm, 0, sizeof(tm));
    tm.tm_year = ld->year - 1900;
    tm.tm_mon  = ld->month - 1;
    tm.tm_mday = ld->day;
    tm.tm_hour = (int)(time_ns / 3600000000000LL);
    tm.tm_min  = (int)((time_ns / 60000000000LL) % 60);
    tm.tm_sec  = (int)((time_ns / 1000000000LL) % 60);
    time_t t = timegm(&tm);
    if (t == (time_t)-1) return (el_val_t)0;
    int64_t ns = (int64_t)t * 1000000000LL + (time_ns % 1000000000LL);
    return (el_val_t)(uintptr_t)_el_caltime_alloc(ns, c);
}

el_val_t local_date_year(el_val_t v) {
    if (!el_is_magic(v, EL_LDATE_MAGIC)) return (el_val_t)0;
    return (el_val_t)((el_localdate_t*)(uintptr_t)v)->year;
}
el_val_t local_date_month(el_val_t v) {
    if (!el_is_magic(v, EL_LDATE_MAGIC)) return (el_val_t)0;
    return (el_val_t)((el_localdate_t*)(uintptr_t)v)->month;
}
el_val_t local_date_day(el_val_t v) {
    if (!el_is_magic(v, EL_LDATE_MAGIC)) return (el_val_t)0;
    return (el_val_t)((el_localdate_t*)(uintptr_t)v)->day;
}
el_val_t local_time_hour(el_val_t v) {
    int64_t t = (int64_t)v;
    return (el_val_t)(t / 3600000000000LL);
}
el_val_t local_time_minute(el_val_t v) {
    int64_t t = (int64_t)v;
    return (el_val_t)((t / 60000000000LL) % 60);
}
el_val_t local_time_second(el_val_t v) {
    int64_t t = (int64_t)v;
    return (el_val_t)((t / 1000000000LL) % 60);
}
el_val_t local_time_nanos(el_val_t v) {
    int64_t t = (int64_t)v;
    return (el_val_t)(t % 1000000000LL);
}

el_val_t el_local_date_add_dur(el_val_t ld_val, el_val_t dur_val) {
    if (!el_is_magic(ld_val, EL_LDATE_MAGIC)) return ld_val;
    el_localdate_t* ld = (el_localdate_t*)(uintptr_t)ld_val;
    int64_t dur_ns = (int64_t)dur_val;
    int64_t days = dur_ns / EL_EARTH_DAY_NS;
    int y = ld->year, m = ld->month, d = ld->day;
    /* Walk days forward/backward in canonical Gregorian. */
    while (days > 0) {
        int dim = _el_days_in_month(y, m);
        if (d + days <= dim) { d += (int)days; days = 0; break; }
        days -= (dim - d + 1);
        d = 1;
        m++;
        if (m > 12) { m = 1; y++; }
    }
    while (days < 0) {
        if (d + days >= 1) { d += (int)days; days = 0; break; }
        days += d;
        m--;
        if (m < 1) { m = 12; y--; }
        d = _el_days_in_month(y, m);
    }
    return local_date((el_val_t)y, (el_val_t)m, (el_val_t)d);
}

el_val_t el_local_time_add_dur(el_val_t lt_val, el_val_t dur_val) {
    int64_t t = (int64_t)lt_val + (int64_t)dur_val;
    /* Wrap mod 24h on Earth-default. CycleCalendar wrapping requires the
     * caller to use cal_in / cal_format for the right modulus. */
    int64_t day = EL_EARTH_DAY_NS;
    int64_t r = t % day;
    if (r < 0) r += day;
    return (el_val_t)r;
}

el_val_t el_local_date_lt(el_val_t a_val, el_val_t b_val) {
    if (!el_is_magic(a_val, EL_LDATE_MAGIC) || !el_is_magic(b_val, EL_LDATE_MAGIC)) return (el_val_t)0;
    el_localdate_t* a = (el_localdate_t*)(uintptr_t)a_val;
    el_localdate_t* b = (el_localdate_t*)(uintptr_t)b_val;
    if (a->year != b->year) return (el_val_t)(a->year < b->year ? 1 : 0);
    if (a->month != b->month) return (el_val_t)(a->month < b->month ? 1 : 0);
    return (el_val_t)(a->day < b->day ? 1 : 0);
}

el_val_t el_local_date_eq(el_val_t a_val, el_val_t b_val) {
    if (!el_is_magic(a_val, EL_LDATE_MAGIC) || !el_is_magic(b_val, EL_LDATE_MAGIC)) return (el_val_t)0;
    el_localdate_t* a = (el_localdate_t*)(uintptr_t)a_val;
    el_localdate_t* b = (el_localdate_t*)(uintptr_t)b_val;
    return (el_val_t)((a->year == b->year && a->month == b->month && a->day == b->day) ? 1 : 0);
}

/* ── Rhythm ──────────────────────────────────────────────────────────────── */

static el_rhythm_t* _el_rhythm_alloc(el_rhythm_kind_t k) {
    el_rhythm_t* r = (el_rhythm_t*)calloc(1, sizeof(el_rhythm_t));
    r->magic = EL_RHYTHM_MAGIC;
    r->kind = k;
    return r;
}

el_val_t rhythm_cycle_start(void) {
    return (el_val_t)(uintptr_t)_el_rhythm_alloc(EL_RHYTHM_CYCLE_START);
}

el_val_t rhythm_cycle_phase(el_val_t phase_val) {
    el_rhythm_t* r = _el_rhythm_alloc(EL_RHYTHM_CYCLE_PHASE);
    r->phase = el_to_float(phase_val);
    return (el_val_t)(uintptr_t)r;
}

el_val_t rhythm_duration(el_val_t d_val) {
    el_rhythm_t* r = _el_rhythm_alloc(EL_RHYTHM_DURATION);
    r->period_ns = (int64_t)d_val;
    return (el_val_t)(uintptr_t)r;
}

el_val_t rhythm_session_start(void) {
    return (el_val_t)(uintptr_t)_el_rhythm_alloc(EL_RHYTHM_SESSION_START);
}

el_val_t rhythm_event(el_val_t name_val) {
    el_rhythm_t* r = _el_rhythm_alloc(EL_RHYTHM_EVENT);
    const char* n = EL_CSTR(name_val);
    r->event_name = el_strdup_persist(n ? n : "");
    return (el_val_t)(uintptr_t)r;
}

el_val_t rhythm_and(el_val_t a_val, el_val_t b_val) {
    el_rhythm_t* r = _el_rhythm_alloc(EL_RHYTHM_AND);
    r->a = el_is_magic(a_val, EL_RHYTHM_MAGIC) ? (el_rhythm_t*)(uintptr_t)a_val : NULL;
    r->b = el_is_magic(b_val, EL_RHYTHM_MAGIC) ? (el_rhythm_t*)(uintptr_t)b_val : NULL;
    return (el_val_t)(uintptr_t)r;
}

el_val_t rhythm_or(el_val_t a_val, el_val_t b_val) {
    el_rhythm_t* r = _el_rhythm_alloc(EL_RHYTHM_OR);
    r->a = el_is_magic(a_val, EL_RHYTHM_MAGIC) ? (el_rhythm_t*)(uintptr_t)a_val : NULL;
    r->b = el_is_magic(b_val, EL_RHYTHM_MAGIC) ? (el_rhythm_t*)(uintptr_t)b_val : NULL;
    return (el_val_t)(uintptr_t)r;
}

el_val_t rhythm_weekday(el_val_t day) {
    el_rhythm_t* r = _el_rhythm_alloc(EL_RHYTHM_WEEKDAY);
    r->weekday = (int)(int64_t)day;
    return (el_val_t)(uintptr_t)r;
}

el_val_t rhythm_weekly_at(el_val_t day, el_val_t hour, el_val_t minute) {
    el_rhythm_t* r = _el_rhythm_alloc(EL_RHYTHM_WEEKLY_AT);
    r->weekday = (int)(int64_t)day;
    r->hour = (int)(int64_t)hour;
    r->minute = (int)(int64_t)minute;
    return (el_val_t)(uintptr_t)r;
}

/* Compute the next instant on or after `after` when rhythm `r` matches,
 * under calendar `cal`. */
static int64_t _el_next_after(el_rhythm_t* r, int64_t after_ns, el_calendar_t* cal) {
    if (!r) return after_ns;
    int64_t period = cal->cycle_period_ns > 0 ? cal->cycle_period_ns : EL_EARTH_DAY_NS;
    switch (r->kind) {
        case EL_RHYTHM_CYCLE_START: {
            int64_t base = after_ns - cal->epoch_ns;
            int64_t cyc = (base / period) + 1;
            return cal->epoch_ns + cyc * period;
        }
        case EL_RHYTHM_CYCLE_PHASE: {
            int64_t base = after_ns - cal->epoch_ns;
            int64_t cyc_ns = (int64_t)(r->phase * (double)period);
            int64_t cur_cyc = base / period;
            int64_t candidate = cal->epoch_ns + cur_cyc * period + cyc_ns;
            if (candidate <= after_ns) candidate += period;
            return candidate;
        }
        case EL_RHYTHM_DURATION: {
            return after_ns + (r->period_ns > 0 ? r->period_ns : 1);
        }
        case EL_RHYTHM_WEEKDAY:
        case EL_RHYTHM_WEEKLY_AT: {
            if (cal->kind != EL_CALENDAR_EARTH) {
                /* Non-Earth calendars: fall back to cycle math, treating
                 * weekday as a 7-cycle-per-period proxy. */
                return after_ns + period;
            }
            _el_apply_zone(cal->zone);
            time_t s = (time_t)(after_ns / 1000000000LL);
            struct tm tm;
            localtime_r(&s, &tm);
            /* tm_wday: 0=Sun..6=Sat. We use 1=Mon..7=Sun. */
            int target = r->weekday >= 1 && r->weekday <= 7 ? r->weekday : 1;
            int target_wday = target == 7 ? 0 : target; /* 7→Sun=0, 1→Mon=1 */
            int days_ahead = (target_wday - tm.tm_wday + 7) % 7;
            int hour = (r->kind == EL_RHYTHM_WEEKLY_AT) ? r->hour : 0;
            int minute = (r->kind == EL_RHYTHM_WEEKLY_AT) ? r->minute : 0;
            struct tm cand = tm;
            cand.tm_mday += days_ahead;
            cand.tm_hour = hour;
            cand.tm_min  = minute;
            cand.tm_sec  = 0;
            cand.tm_isdst = -1;
            time_t cand_t = mktime(&cand);
            int64_t cand_ns = (int64_t)cand_t * 1000000000LL;
            if (cand_ns <= after_ns) {
                cand.tm_mday += 7;
                cand.tm_isdst = -1;
                cand_t = mktime(&cand);
                cand_ns = (int64_t)cand_t * 1000000000LL;
            }
            return cand_ns;
        }
        case EL_RHYTHM_AND: {
            int64_t a = _el_next_after(r->a, after_ns, cal);
            int64_t b = _el_next_after(r->b, after_ns, cal);
            return a > b ? a : b;
        }
        case EL_RHYTHM_OR: {
            int64_t a = _el_next_after(r->a, after_ns, cal);
            int64_t b = _el_next_after(r->b, after_ns, cal);
            return a < b ? a : b;
        }
        case EL_RHYTHM_SESSION_START:
        case EL_RHYTHM_EVENT:
        default:
            return after_ns;
    }
}

el_val_t rhythm_next_after(el_val_t r_val, el_val_t after_val, el_val_t cal_val) {
    if (!el_is_magic(r_val, EL_RHYTHM_MAGIC)) return after_val;
    el_rhythm_t* r = (el_rhythm_t*)(uintptr_t)r_val;
    el_calendar_t* c = _el_resolve_cal(cal_val);
    int64_t out = _el_next_after(r, (int64_t)after_val, c);
    return (el_val_t)out;
}

el_val_t rhythm_matches(el_val_t r_val, el_val_t ct_val) {
    if (!el_is_magic(r_val, EL_RHYTHM_MAGIC)) return (el_val_t)0;
    if (!el_is_magic(ct_val, EL_CALTIME_MAGIC)) return (el_val_t)0;
    el_rhythm_t* r = (el_rhythm_t*)(uintptr_t)r_val;
    el_caltime_t* ct = (el_caltime_t*)(uintptr_t)ct_val;
    int64_t period = ct->cal->cycle_period_ns > 0 ? ct->cal->cycle_period_ns : EL_EARTH_DAY_NS;
    int64_t base = ct->instant_ns - ct->cal->epoch_ns;
    int64_t phase_ns = base % period;
    if (phase_ns < 0) phase_ns += period;
    double phase = (double)phase_ns / (double)period;
    switch (r->kind) {
        case EL_RHYTHM_CYCLE_START: return (el_val_t)(phase_ns == 0 ? 1 : 0);
        case EL_RHYTHM_CYCLE_PHASE: {
            double diff = phase - r->phase;
            if (diff < 0) diff = -diff;
            return (el_val_t)(diff < 0.001 ? 1 : 0);
        }
        default: return (el_val_t)0;
    }
}

/* ── UUID v4 ─────────────────────────────────────────────────────────────── */

static int _el_uuid_seeded = 0;

static void _el_uuid_seed(void) {
    if (!_el_uuid_seeded) {
        srand((unsigned)time(NULL) ^ (unsigned)(uintptr_t)&_el_uuid_seeded);
        _el_uuid_seeded = 1;
    }
}

el_val_t uuid_new(void) {
    _el_uuid_seed();
    unsigned char b[16];
    for (int i = 0; i < 16; i++) b[i] = (unsigned char)(rand() & 0xff);
    /* Version 4 */
    b[6] = (b[6] & 0x0f) | 0x40;
    /* RFC 4122 variant */
    b[8] = (b[8] & 0x3f) | 0x80;
    char buf[37];
    snprintf(buf, sizeof(buf),
             "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
             b[0], b[1], b[2], b[3],
             b[4], b[5],
             b[6], b[7],
             b[8], b[9],
             b[10], b[11], b[12], b[13], b[14], b[15]);
    return el_wrap_str(el_strdup(buf));
}

el_val_t uuid_v4(void) { return uuid_new(); }

/* ── Environment ─────────────────────────────────────────────────────────── */

el_val_t env(el_val_t key) {
    const char* k = EL_CSTR(key);
    if (!k) return el_wrap_str(el_strdup(""));
    const char* v = getenv(k);
    return el_wrap_str(el_strdup(v ? v : ""));
}

/* ── In-process state K/V ────────────────────────────────────────────────── */

typedef struct {
    char* key;
    char* value;
} StateEntry;

static StateEntry*      _state_entries = NULL;
static size_t           _state_count   = 0;
static size_t           _state_cap     = 0;
/* Mutex protecting all _state_entries access. state_set/state_get are called
 * concurrently from 64 HTTP worker threads — without this lock, realloc and
 * free race, producing corruption, double-free, and segfaults. */
static pthread_mutex_t  _state_mu = PTHREAD_MUTEX_INITIALIZER;

static StateEntry* state_find(const char* key) {
    for (size_t i = 0; i < _state_count; i++) {
        if (strcmp(_state_entries[i].key, key) == 0) return &_state_entries[i];
    }
    return NULL;
}

el_val_t state_set(el_val_t key, el_val_t value) {
    const char* k = EL_CSTR(key);
    const char* v = EL_CSTR(value);
    if (!k) return 0;
    if (!v) v = "";
    pthread_mutex_lock(&_state_mu);
    StateEntry* e = state_find(k);
    if (e) {
        free(e->value);
        e->value = el_strdup_persist(v);
        pthread_mutex_unlock(&_state_mu);
        return 1;
    }
    if (_state_count >= _state_cap) {
        size_t nc = _state_cap == 0 ? 16 : _state_cap * 2;
        StateEntry* grown = realloc(_state_entries, nc * sizeof(StateEntry));
        if (!grown) { pthread_mutex_unlock(&_state_mu); fputs("el_runtime: out of memory\n", stderr); exit(1); }
        _state_entries = grown;
        _state_cap = nc;
    }
    _state_entries[_state_count].key   = el_strdup_persist(k);
    _state_entries[_state_count].value = el_strdup_persist(v);
    _state_count++;
    pthread_mutex_unlock(&_state_mu);
    return 1;
}

el_val_t state_get(el_val_t key) {
    const char* k = EL_CSTR(key);
    if (!k) return el_wrap_str(el_strdup(""));
    pthread_mutex_lock(&_state_mu);
    StateEntry* e = state_find(k);
    char* result = el_strdup_persist(e ? e->value : "");
    pthread_mutex_unlock(&_state_mu);
    /* wrap in arena-tracked copy for the caller's request lifetime */
    char* copy = el_strdup(result);
    return el_wrap_str(copy);
}

el_val_t state_del(el_val_t key) {
    const char* k = EL_CSTR(key);
    if (!k) return 0;
    pthread_mutex_lock(&_state_mu);
    for (size_t i = 0; i < _state_count; i++) {
        if (strcmp(_state_entries[i].key, k) == 0) {
            free(_state_entries[i].key);
            free(_state_entries[i].value);
            for (size_t j = i + 1; j < _state_count; j++) {
                _state_entries[j - 1] = _state_entries[j];
            }
            _state_count--;
            pthread_mutex_unlock(&_state_mu);
            return 1;
        }
    }
    pthread_mutex_unlock(&_state_mu);
    return 1;
}

el_val_t state_keys(void) {
    pthread_mutex_lock(&_state_mu);
    /* Build a JSON array string: ["key1","key2",...] */
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '[');
    for (size_t i = 0; i < _state_count; i++) {
        if (i > 0) jb_putc(&b, ',');
        jb_putc(&b, '"');
        jb_emit_escaped(&b, _state_entries[i].key);
        jb_putc(&b, '"');
    }
    jb_putc(&b, ']');
    pthread_mutex_unlock(&_state_mu);
    return el_wrap_str(b.buf);
}

/* Returns 1 (true) if the key is present in the state store, else 0 (false). */
el_val_t state_has(el_val_t key) {
    const char* k = EL_CSTR(key);
    if (!k) return 0;
    pthread_mutex_lock(&_state_mu);
    StateEntry* e = state_find(k);
    int found = (e != NULL) ? 1 : 0;
    pthread_mutex_unlock(&_state_mu);
    return (el_val_t)found;
}

/* Returns the value for key, or default_val if the key is absent. */
el_val_t state_get_or(el_val_t key, el_val_t default_val) {
    const char* k = EL_CSTR(key);
    if (!k) return default_val;
    pthread_mutex_lock(&_state_mu);
    StateEntry* e = state_find(k);
    if (e) {
        char* copy = el_strdup(e->value);
        pthread_mutex_unlock(&_state_mu);
        return el_wrap_str(copy);
    }
    pthread_mutex_unlock(&_state_mu);
    return default_val;
}

/* ── Float formatting ────────────────────────────────────────────────────── */

el_val_t float_to_str(el_val_t f) {
    char buf[64];
    double v = el_to_float(f);
    /* Normalize NaN to "nan" regardless of sign — platform-independent. */
    if (isnan(v)) {
        snprintf(buf, sizeof(buf), "nan");
    } else {
        snprintf(buf, sizeof(buf), "%g", v);
    }
    return el_wrap_str(el_strdup(buf));
}

el_val_t int_to_float(el_val_t n) {
    return el_from_float((double)(int64_t)n);
}

el_val_t float_to_int(el_val_t f) {
    return (el_val_t)(int64_t)el_to_float(f);
}

el_val_t format_float(el_val_t f, el_val_t decimals) {
    int d = (int)(int64_t)decimals;
    if (d < 0)   d = 0;
    if (d > 30)  d = 30;
    char buf[128];
    snprintf(buf, sizeof(buf), "%.*f", d, el_to_float(f));
    return el_wrap_str(el_strdup(buf));
}

el_val_t decimal_round(el_val_t f, el_val_t decimals) {
    int d = (int)(int64_t)decimals;
    if (d < 0)  d = 0;
    if (d > 15) d = 15;
    double mul = pow(10.0, (double)d);
    double v = el_to_float(f);
    double r = (v >= 0.0 ? floor(v * mul + 0.5) : -floor(-v * mul + 0.5)) / mul;
    return el_from_float(r);
}

el_val_t str_to_float(el_val_t s) {
    const char* str = EL_CSTR(s);
    if (!str) return el_from_float(0.0);
    return el_from_float(strtod(str, NULL));
}

/* ── Math (Float-aware) ──────────────────────────────────────────────────── */

el_val_t math_sqrt(el_val_t f) { return el_from_float(sqrt(el_to_float(f))); }
el_val_t math_log(el_val_t f)  { return el_from_float(log(el_to_float(f))); }
el_val_t math_ln(el_val_t f)   { return el_from_float(log(el_to_float(f))); }
el_val_t math_sin(el_val_t f)  { return el_from_float(sin(el_to_float(f))); }
el_val_t math_cos(el_val_t f)  { return el_from_float(cos(el_to_float(f))); }
el_val_t math_pi(void)         { return el_from_float(3.141592653589793238462643383279502884); }

/* ── String additions ────────────────────────────────────────────────────── */

el_val_t str_index_of(el_val_t s, el_val_t sub) {
    const char* str = EL_CSTR(s);
    const char* sb  = EL_CSTR(sub);
    if (!str || !sb) return -1;
    const char* hit = strstr(str, sb);
    if (!hit) return -1;
    return (el_val_t)(int64_t)(hit - str);
}

el_val_t str_split(el_val_t s, el_val_t sep) {
    const char* str = EL_CSTR(s);
    const char* sp  = EL_CSTR(sep);
    el_val_t lst = el_list_empty();
    if (!str) return lst;
    if (!sp || !*sp) {
        lst = el_list_append(lst, el_wrap_str(el_strdup(str)));
        return lst;
    }
    size_t lp = strlen(sp);
    const char* p = str;
    const char* hit;
    while ((hit = strstr(p, sp)) != NULL) {
        size_t n = (size_t)(hit - p);
        char* out = el_strbuf(n);
        memcpy(out, p, n);
        out[n] = '\0';
        lst = el_list_append(lst, el_wrap_str(out));
        p = hit + lp;
    }
    lst = el_list_append(lst, el_wrap_str(el_strdup(p)));
    return lst;
}

el_val_t str_char_at(el_val_t s, el_val_t i) {
    const char* str = EL_CSTR(s);
    int64_t idx = (int64_t)i;
    if (!str) return el_wrap_str(el_strdup(""));
    int64_t n = (int64_t)strlen(str);
    if (idx < 0 || idx >= n) return el_wrap_str(el_strdup(""));
    char buf[2];
    buf[0] = str[idx];
    buf[1] = '\0';
    return el_wrap_str(el_strdup(buf));
}

el_val_t str_char_code(el_val_t s, el_val_t i) {
    const char* str = EL_CSTR(s);
    int64_t idx = (int64_t)i;
    if (!str) return 0;
    int64_t n = (int64_t)strlen(str);
    if (idx < 0 || idx >= n) return 0;
    return (el_val_t)(unsigned char)str[idx];
}

static el_val_t str_pad(const char* s, int64_t width, const char* pad, int left) {
    if (!s) s = "";
    if (!pad || !*pad) pad = " ";
    int64_t lp = (int64_t)strlen(pad);
    int64_t ls = (int64_t)strlen(s);
    if (ls >= width) return el_wrap_str(el_strdup(s));
    int64_t need = width - ls;
    char* out = el_strbuf((size_t)width);
    if (left) {
        for (int64_t i = 0; i < need; i++) out[i] = pad[i % lp];
        memcpy(out + need, s, (size_t)ls);
    } else {
        memcpy(out, s, (size_t)ls);
        for (int64_t i = 0; i < need; i++) out[ls + i] = pad[i % lp];
    }
    out[width] = '\0';
    return el_wrap_str(out);
}

el_val_t str_pad_left(el_val_t s, el_val_t width, el_val_t pad) {
    return str_pad(EL_CSTR(s), (int64_t)width, EL_CSTR(pad), 1);
}

el_val_t str_pad_right(el_val_t s, el_val_t width, el_val_t pad) {
    return str_pad(EL_CSTR(s), (int64_t)width, EL_CSTR(pad), 0);
}

el_val_t str_format(el_val_t fmt, el_val_t data) {
    const char* tpl = EL_CSTR(fmt);
    if (!tpl) return el_wrap_str(el_strdup(""));
    JsonBuf b; jb_init(&b);
    const char* p = tpl;
    while (*p) {
        if (*p == '{') {
            const char* q = p + 1;
            while (*q && *q != '}') q++;
            if (*q == '}') {
                size_t klen = (size_t)(q - p - 1);
                char keybuf[256];
                if (klen < sizeof(keybuf)) {
                    memcpy(keybuf, p + 1, klen);
                    keybuf[klen] = '\0';
                    el_val_t v = el_map_get(data, EL_STR(keybuf));
                    if (v != 0 && looks_like_string(v)) {
                        jb_puts(&b, EL_CSTR(v));
                        p = q + 1;
                        continue;
                    } else if (v != 0) {
                        jb_emit_int(&b, (int64_t)v);
                        p = q + 1;
                        continue;
                    }
                }
                /* Unknown key — leave {key} verbatim */
                jb_reserve(&b, klen + 2);
                memcpy(b.buf + b.len, p, klen + 2);
                b.len += klen + 2;
                b.buf[b.len] = '\0';
                p = q + 1;
                continue;
            }
        }
        jb_putc(&b, *p);
        p++;
    }
    return el_wrap_str(b.buf);
}

el_val_t str_lower(el_val_t s) { return str_to_lower(s); }
el_val_t str_upper(el_val_t s) { return str_to_upper(s); }

/* ── Text-processing primitives (Phase 1: byte/codepoint, ASCII char classes)
 *
 * Phase 1 covers the operations every text-handling caller used to roll by
 * hand on top of str_index_of + str_slice. The character-class predicates
 * (is_letter / is_digit / ...) are ASCII only — Unicode-grapheme awareness,
 * NFC/NFD normalization, and regex are Phase 2. Single-char input checks the
 * first byte; multi-char input requires ALL bytes to match (false otherwise).
 *
 * Counting:
 *   str_count            non-overlapping occurrences of sub in s
 *   str_count_chars      codepoint count (UTF-8 leading-byte count)
 *   str_count_bytes      explicit byte length (alias of str_len)
 *   str_count_lines      \n-delimited line count (\r\n folded to \n)
 *   str_count_words      whitespace-delimited tokens, non-empty only
 *   str_count_letters    ASCII [A-Za-z]
 *   str_count_digits     ASCII [0-9]
 *
 * Find / position:
 *   str_index_of_all     all byte offsets of sub, [] if none
 *   str_last_index_of    last byte offset of sub, -1 if not found
 *   str_find_chars       first index of any char in any_of, -1 if none
 *
 * Transform:
 *   str_repeat           s * n (non-negative)
 *   str_reverse          codepoint-reversed (NOT grapheme-aware)
 *   str_strip_prefix     s without prefix if present, else s
 *   str_strip_suffix     s without suffix if present, else s
 *   str_strip_chars      strip leading+trailing chars matching any in chars
 *   str_lstrip           strip leading whitespace
 *   str_rstrip           strip trailing whitespace
 *
 * Char classification (Bool):
 *   is_letter, is_digit, is_alphanumeric, is_whitespace,
 *   is_punctuation, is_uppercase, is_lowercase
 *
 * Splitting:
 *   str_split_lines      \n-delimited (\r\n folded). Trailing empty dropped.
 *   str_split_chars      alias of native_string_chars in str_ namespace
 *   str_split_n          split into at most n parts (last part keeps the
 *                        rest verbatim, including any further separators)
 *
 * Joining:
 *   str_join             [String] -> String, sep between elements
 */

/* Count non-overlapping occurrences of sub in s. Empty sub returns 0. */
el_val_t str_count(el_val_t sv, el_val_t subv) {
    const char* s   = EL_CSTR(sv);
    const char* sub = EL_CSTR(subv);
    if (!s || !sub || !*sub) return 0;
    size_t lp = strlen(sub);
    int64_t count = 0;
    const char* p = s;
    while ((p = strstr(p, sub)) != NULL) {
        count++;
        p += lp;   /* non-overlapping advance */
    }
    return (el_val_t)count;
}

/* Codepoint count: walk bytes, count those NOT matching 10xxxxxx. */
el_val_t str_count_chars(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return 0;
    int64_t count = 0;
    for (const unsigned char* p = (const unsigned char*)s; *p; p++) {
        if ((*p & 0xC0) != 0x80) count++;
    }
    return (el_val_t)count;
}

el_val_t str_count_bytes(el_val_t sv) {
    return str_len(sv);
}

el_val_t str_count_lines(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s || !*s) return 0;
    int64_t count = 0;
    int has_content = 0;
    for (const char* p = s; *p; p++) {
        has_content = 1;
        if (*p == '\n') {
            count++;
            has_content = 0;   /* the \n closed the line */
        }
    }
    if (has_content) count++;   /* trailing line with no terminator */
    return (el_val_t)count;
}

el_val_t str_count_words(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return 0;
    int64_t count = 0;
    int in_word = 0;
    for (const unsigned char* p = (const unsigned char*)s; *p; p++) {
        if (isspace(*p)) {
            in_word = 0;
        } else if (!in_word) {
            in_word = 1;
            count++;
        }
    }
    return (el_val_t)count;
}

el_val_t str_count_letters(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return 0;
    int64_t count = 0;
    for (const unsigned char* p = (const unsigned char*)s; *p; p++) {
        if ((*p >= 'A' && *p <= 'Z') || (*p >= 'a' && *p <= 'z')) count++;
    }
    return (el_val_t)count;
}

el_val_t str_count_digits(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return 0;
    int64_t count = 0;
    for (const unsigned char* p = (const unsigned char*)s; *p; p++) {
        if (*p >= '0' && *p <= '9') count++;
    }
    return (el_val_t)count;
}

el_val_t str_index_of_all(el_val_t sv, el_val_t subv) {
    const char* s   = EL_CSTR(sv);
    const char* sub = EL_CSTR(subv);
    el_val_t lst = el_list_empty();
    if (!s || !sub || !*sub) return lst;
    size_t lp = strlen(sub);
    const char* p = s;
    const char* hit;
    while ((hit = strstr(p, sub)) != NULL) {
        lst = el_list_append(lst, (el_val_t)(int64_t)(hit - s));
        p = hit + lp;
    }
    return lst;
}

el_val_t str_last_index_of(el_val_t sv, el_val_t subv) {
    const char* s   = EL_CSTR(sv);
    const char* sub = EL_CSTR(subv);
    if (!s || !sub || !*sub) return -1;
    size_t lp = strlen(sub);
    int64_t last = -1;
    const char* p = s;
    const char* hit;
    while ((hit = strstr(p, sub)) != NULL) {
        last = (int64_t)(hit - s);
        p = hit + lp;
    }
    return (el_val_t)last;
}

el_val_t str_find_chars(el_val_t sv, el_val_t any_of_v) {
    const char* s     = EL_CSTR(sv);
    const char* any   = EL_CSTR(any_of_v);
    if (!s || !any || !*any) return -1;
    for (const char* p = s; *p; p++) {
        if (strchr(any, *p)) return (el_val_t)(int64_t)(p - s);
    }
    return -1;
}

el_val_t str_repeat(el_val_t sv, el_val_t nv) {
    const char* s = EL_CSTR(sv);
    int64_t n = (int64_t)nv;
    if (!s || n <= 0) return el_wrap_str(el_strdup(""));
    size_t ls = strlen(s);
    if (ls == 0) return el_wrap_str(el_strdup(""));
    size_t total = ls * (size_t)n;
    char* out = el_strbuf(total);
    for (int64_t i = 0; i < n; i++) {
        memcpy(out + i * ls, s, ls);
    }
    out[total] = '\0';
    return el_wrap_str(out);
}

/* Reverse by codepoint: walk codepoints, copy each backwards into the output.
 * NOT grapheme-aware (Phase 2). Combining marks attached to a base codepoint
 * will detach. ASCII strings are byte-reverse equivalent. */
el_val_t str_reverse(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return el_wrap_str(el_strdup(""));
    size_t n = strlen(s);
    char* out = el_strbuf(n);
    /* Walk forward, find each codepoint's byte length, then copy from the end. */
    size_t out_pos = n;
    const unsigned char* p = (const unsigned char*)s;
    while (*p) {
        int cp_len;
        if      ((*p & 0x80) == 0x00) cp_len = 1;
        else if ((*p & 0xE0) == 0xC0) cp_len = 2;
        else if ((*p & 0xF0) == 0xE0) cp_len = 3;
        else if ((*p & 0xF8) == 0xF0) cp_len = 4;
        else                          cp_len = 1;   /* invalid byte: passthrough */
        out_pos -= cp_len;
        memcpy(out + out_pos, p, cp_len);
        p += cp_len;
    }
    out[n] = '\0';
    return el_wrap_str(out);
}

el_val_t str_strip_prefix(el_val_t sv, el_val_t prefv) {
    const char* s    = EL_CSTR(sv);
    const char* pref = EL_CSTR(prefv);
    if (!s) return el_wrap_str(el_strdup(""));
    if (!pref || !*pref) return el_wrap_str(el_strdup(s));
    size_t lp = strlen(pref);
    size_t ls = strlen(s);
    if (lp <= ls && strncmp(s, pref, lp) == 0) {
        char* out = el_strbuf(ls - lp);
        memcpy(out, s + lp, ls - lp);
        out[ls - lp] = '\0';
        return el_wrap_str(out);
    }
    return el_wrap_str(el_strdup(s));
}

el_val_t str_strip_suffix(el_val_t sv, el_val_t sufv) {
    const char* s   = EL_CSTR(sv);
    const char* suf = EL_CSTR(sufv);
    if (!s) return el_wrap_str(el_strdup(""));
    if (!suf || !*suf) return el_wrap_str(el_strdup(s));
    size_t ls   = strlen(s);
    size_t lsuf = strlen(suf);
    if (lsuf <= ls && strcmp(s + ls - lsuf, suf) == 0) {
        char* out = el_strbuf(ls - lsuf);
        memcpy(out, s, ls - lsuf);
        out[ls - lsuf] = '\0';
        return el_wrap_str(out);
    }
    return el_wrap_str(el_strdup(s));
}

el_val_t str_strip_chars(el_val_t sv, el_val_t charsv) {
    const char* s     = EL_CSTR(sv);
    const char* chars = EL_CSTR(charsv);
    if (!s) return el_wrap_str(el_strdup(""));
    if (!chars || !*chars) return el_wrap_str(el_strdup(s));
    const char* start = s;
    while (*start && strchr(chars, *start)) start++;
    size_t n = strlen(start);
    while (n > 0 && strchr(chars, start[n - 1])) n--;
    char* out = el_strbuf(n);
    memcpy(out, start, n);
    out[n] = '\0';
    return el_wrap_str(out);
}

el_val_t str_lstrip(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return el_wrap_str(el_strdup(""));
    while (*s && isspace((unsigned char)*s)) s++;
    return el_wrap_str(el_strdup(s));
}

el_val_t str_rstrip(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) return el_wrap_str(el_strdup(""));
    size_t n = strlen(s);
    while (n > 0 && isspace((unsigned char)s[n - 1])) n--;
    char* out = el_strbuf(n);
    memcpy(out, s, n);
    out[n] = '\0';
    return el_wrap_str(out);
}

/* Character classification.
 * Empty input returns false. Multi-char input requires ALL bytes to match.
 * ASCII range only; Phase 2 will widen to Unicode. */
static int s_all_match(el_val_t sv, int (*pred)(unsigned char)) {
    const char* s = EL_CSTR(sv);
    if (!s || !*s) return 0;
    for (const unsigned char* p = (const unsigned char*)s; *p; p++) {
        if (!pred(*p)) return 0;
    }
    return 1;
}

static int p_letter(unsigned char c)   { return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z'); }
static int p_digit(unsigned char c)    { return c >= '0' && c <= '9'; }
static int p_alnum(unsigned char c)    { return p_letter(c) || p_digit(c); }
static int p_white(unsigned char c)    { return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == '\f' || c == '\v'; }
static int p_punct(unsigned char c)    { return ispunct(c) ? 1 : 0; }
static int p_upper(unsigned char c)    { return c >= 'A' && c <= 'Z'; }
static int p_lower(unsigned char c)    { return c >= 'a' && c <= 'z'; }

el_val_t is_letter(el_val_t s)        { return (el_val_t)s_all_match(s, p_letter); }
el_val_t is_digit(el_val_t s)         { return (el_val_t)s_all_match(s, p_digit); }
el_val_t is_alphanumeric(el_val_t s)  { return (el_val_t)s_all_match(s, p_alnum); }
el_val_t is_whitespace(el_val_t s)    { return (el_val_t)s_all_match(s, p_white); }
el_val_t is_punctuation(el_val_t s)   { return (el_val_t)s_all_match(s, p_punct); }
el_val_t is_uppercase(el_val_t s)     { return (el_val_t)s_all_match(s, p_upper); }
el_val_t is_lowercase(el_val_t s)     { return (el_val_t)s_all_match(s, p_lower); }

/* Split on \n. \r\n is folded to \n first. Trailing empty after final \n
 * is dropped (so "a\nb\n" -> ["a", "b"], not ["a", "b", ""]). */
el_val_t str_split_lines(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    el_val_t lst = el_list_empty();
    if (!s) return lst;
    size_t n = strlen(s);
    /* Pre-scan: build into a normalized buffer with \r\n folded. */
    const char* line_start = s;
    for (size_t i = 0; i <= n; i++) {
        if (s[i] == '\n' || s[i] == '\0') {
            size_t len = (size_t)(s + i - line_start);
            /* Drop trailing \r if this was \r\n. */
            if (len > 0 && line_start[len - 1] == '\r') len--;
            /* Drop final trailing-empty-after-newline. */
            if (s[i] == '\0' && len == 0 && i > 0 && s[i - 1] == '\n') break;
            char* out = el_strbuf(len);
            memcpy(out, line_start, len);
            out[len] = '\0';
            lst = el_list_append(lst, el_wrap_str(out));
            if (s[i] == '\0') break;
            line_start = s + i + 1;
        }
    }
    return lst;
}

el_val_t str_split_chars(el_val_t s) {
    return native_string_chars(s);
}

/* Split into at most n parts. The (n-1)th split point is the LAST split;
 * after it, the remainder is appended verbatim including any further
 * separators. n <= 0 returns an empty list. n == 1 returns [s]. */
el_val_t str_split_n(el_val_t sv, el_val_t sepv, el_val_t nv) {
    const char* s   = EL_CSTR(sv);
    const char* sep = EL_CSTR(sepv);
    int64_t n = (int64_t)nv;
    el_val_t lst = el_list_empty();
    if (!s) return lst;
    if (n <= 0) return lst;
    if (n == 1 || !sep || !*sep) {
        lst = el_list_append(lst, el_wrap_str(el_strdup(s)));
        return lst;
    }
    size_t lp = strlen(sep);
    const char* p = s;
    int64_t parts = 0;
    const char* hit;
    while (parts < n - 1 && (hit = strstr(p, sep)) != NULL) {
        size_t len = (size_t)(hit - p);
        char* out = el_strbuf(len);
        memcpy(out, p, len);
        out[len] = '\0';
        lst = el_list_append(lst, el_wrap_str(out));
        p = hit + lp;
        parts++;
    }
    /* Remainder verbatim. */
    lst = el_list_append(lst, el_wrap_str(el_strdup(p)));
    return lst;
}

/* Join a [String] with a separator. Empty list -> "". Single-element ->
 * that element. Non-string elements are stringified via int_to_str. */
el_val_t str_join(el_val_t listv, el_val_t sepv) {
    return list_join(listv, sepv);
}

/* ── List additions ──────────────────────────────────────────────────────── */

el_val_t list_push(el_val_t list, el_val_t elem) {
    return el_list_append(list, elem);
}

el_val_t list_push_front(el_val_t listv, el_val_t elem) {
    ElList* lst = (ElList*)(uintptr_t)listv;
    if (!lst) {
        el_val_t nl = el_list_empty();
        return el_list_append(nl, elem);
    }
    /* Append to grow capacity, then shift right */
    listv = el_list_append(listv, elem);
    lst = (ElList*)(uintptr_t)listv;
    for (int64_t i = lst->length - 1; i > 0; i--) {
        lst->elems[i] = lst->elems[i - 1];
    }
    lst->elems[0] = elem;
    return EL_STR(lst);
}

el_val_t list_join(el_val_t listv, el_val_t sep) {
    ElList* lst = (ElList*)(uintptr_t)listv;
    const char* sp = EL_CSTR(sep);
    if (!sp) sp = "";
    if (!lst || lst->length == 0) return el_wrap_str(el_strdup(""));
    JsonBuf b; jb_init(&b);
    for (int64_t i = 0; i < lst->length; i++) {
        if (i > 0) jb_puts(&b, sp);
        el_val_t v = lst->elems[i];
        if (v == 0) continue;
        if (looks_like_string(v)) {
            jb_puts(&b, EL_CSTR(v));
        } else {
            char tmp[32];
            snprintf(tmp, sizeof(tmp), "%lld", (long long)v);
            jb_puts(&b, tmp);
        }
    }
    return el_wrap_str(b.buf);
}

el_val_t list_range(el_val_t start, el_val_t end) {
    int64_t a = (int64_t)start;
    int64_t b = (int64_t)end;
    el_val_t lst = el_list_empty();
    for (int64_t i = a; i < b; i++) lst = el_list_append(lst, (el_val_t)i);
    return lst;
}

/* ── Bool helpers ────────────────────────────────────────────────────────── */

el_val_t bool_to_str(el_val_t b) {
    return el_wrap_str(el_strdup(b ? "true" : "false"));
}

/* ── Numeric parsing ─────────────────────────────────────────────────────── */

/* parse_int — strtoll with a default. str_to_int already exists but does not
 * distinguish "0" from a parse failure, so callers that need a sentinel use
 * this. Skips leading whitespace; accepts an optional leading +/-; returns
 * default_val on empty input or no consumed digits. Trailing junk is ignored
 * (atoi-style). */
el_val_t parse_int(el_val_t sv, el_val_t default_val) {
    const char* s = EL_CSTR(sv);
    if (!s) return default_val;
    while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++;
    if (*s == '\0') return default_val;
    char* end = NULL;
    long long n = strtoll(s, &end, 10);
    if (end == s) return default_val;
    return (el_val_t)n;
}

/* ── Process ─────────────────────────────────────────────────────────────── */

el_val_t exit_program(el_val_t code) {
    exit((int)code);
    return 0; /* unreachable */
}

/* getpid_now — current process id. Named with the _now suffix to avoid
 * colliding with the libc `getpid` declaration that the runtime already
 * sees via <unistd.h> (calling it `getpid` would fight the prototype). */
el_val_t getpid_now(void) {
    return (el_val_t)getpid();
}

/* el_mem_check — self-terminating memory guard for long-running compiler runs.
 *
 * Call this periodically (e.g. after each function compiled) to detect runaway
 * memory growth before the OS OOM-killer fires. Reads the limit from the env
 * var ELC_MAX_MEM_MB (default 512 MB). If resident set size exceeds the limit,
 * prints a diagnostic to stderr and exits with code 1 so the caller (elb or a
 * CI script) can handle the failure gracefully instead of having the whole
 * machine go down.
 *
 * Platform notes:
 *   macOS  — ru_maxrss is in bytes.
 *   Linux  — ru_maxrss is in kilobytes.
 * We normalise to MB before comparing.
 *
 * Returns 0 always (the only non-return path is the exit() branch).
 */
el_val_t el_mem_check(void) {
    /* Read limit from env; default 512 MB. */
    long limit_mb = 512;
    const char *env_val = getenv("ELC_MAX_MEM_MB");
    if (env_val && *env_val) {
        long v = atol(env_val);
        if (v > 0) limit_mb = v;
    }

    struct rusage ru;
    if (getrusage(RUSAGE_SELF, &ru) != 0) return 0; /* can't read — skip check */

    long rss_mb;
#if defined(__APPLE__) || defined(__MACH__)
    /* macOS: ru_maxrss is bytes */
    rss_mb = (long)(ru.ru_maxrss / (1024L * 1024L));
#else
    /* Linux: ru_maxrss is kilobytes */
    rss_mb = (long)(ru.ru_maxrss / 1024L);
#endif

    if (rss_mb >= limit_mb) {
        fprintf(stderr, "elc: memory limit exceeded (%ldMB), aborting\n", limit_mb);
        exit(1);
    }
    return 0;
}

/* ── args() — command-line argument access ──────────────────────────────────
 * Compiled El programs call args() to get a list of CLI arguments.
 * Call el_runtime_init_args(argc, argv) at the start of C main() to populate.
 * The args list excludes argv[0] (the program name).               */

static el_val_t _el_args_list = 0;

void el_runtime_init_args(int argc, char** argv) {
    _el_args_list = el_list_empty();
    for (int i = 1; i < argc; i++) {
        _el_args_list = el_list_append(_el_args_list, EL_STR(argv[i]));
    }
}

el_val_t args(void) {
    if (!_el_args_list) _el_args_list = el_list_empty();
    return _el_args_list;
}

/* ── CGI identity ────────────────────────────────────────────────────────────
 * Called once at program start by the generated main() of a cgi {} program.
 * Stores CGI identity so dharma_* builtins can reference it.               */

static const char* _el_cgi_name      = NULL;
static const char* _el_cgi_dharma_id = NULL;
static const char* _el_cgi_principal = NULL;
static const char* _el_cgi_network   = NULL;
static const char* _el_cgi_engram    = NULL;

void el_cgi_init(el_val_t name, el_val_t dharma_id, el_val_t principal,
                 el_val_t network, el_val_t engram) {
    _el_cgi_name      = EL_CSTR(name);
    _el_cgi_dharma_id = EL_CSTR(dharma_id);
    _el_cgi_principal = EL_CSTR(principal);
    _el_cgi_network   = EL_CSTR(network)   ? EL_CSTR(network)   : "dharma-mainnet";
    _el_cgi_engram    = EL_CSTR(engram)    ? EL_CSTR(engram)    : "http://localhost:8742";
    printf("[cgi] identity: name=%s dharma_id=%s principal=%s network=%s engram=%s\n",
           _el_cgi_name      ? _el_cgi_name      : "(unset)",
           _el_cgi_dharma_id ? _el_cgi_dharma_id : "(unset)",
           _el_cgi_principal ? _el_cgi_principal : "(unset)",
           _el_cgi_network,
           _el_cgi_engram);
}


/* ── Batch 3: Engram in-process graph store ──────────────────────────────── */
/*
 * Single global EngramStore allocated lazily on first call. All node and
 * edge content strings are owned (strdup'd) by the store. Linear arrays
 * with doubling capacity for both nodes and edges.
 *
 * Two-layer activation algorithm (engram_activate):
 *
 * LAYER 1 — Broad fan-out (background activation):
 *   1. Find seed nodes whose content/label/tags contain query (case-insens).
 *   2. BFS up to `depth` hops along ALL edges (excitatory and inhibitory).
 *      Every reachable node fires — nothing is filtered at this layer.
 *   3. bg_act = seed.salience * temporal_decay * dampening
 *      propagated as: new_bg = parent_bg * edge_weight * 0.7 * (1 + tbonus)
 *      where tbonus ∈ {0, 0.10, 0.20} for co-temporal nodes.
 *   4. If reached by multiple paths, take max background_activation.
 *   5. Persist background_activation to EngramNode.background_activation.
 *
 * LAYER 2 — Executive filter (working memory promotion):
 *   6. For each inhibitory edge where source has background_activation > 0:
 *        inhibition[target] = max(bg[source] * e->weight)
 *   7. For each background-activated node:
 *        raw_wm = bg * goal_bias(node, query) * confidence
 *               * (1 - (1 - INHIBITION_FACTOR) * inhibition)
 *   8. Per-type threshold gate: raw_wm >= type_threshold → promoted.
 *        Safety/DharmaSelf: 0.05  Canonical: 0.15  Lesson: 0.25
 *        Belief/Entity: 0.30      Note/Memory/Working: 0.40
 *   9. If not promoted: suppression_count++. After
 *      ENGRAM_SUPPRESSION_BREAKTHROUGH suppressions → force breakthrough
 *      at ENGRAM_BREAKTHROUGH_WEIGHT (latent tension surfacing).
 *  10. Persist working_memory_weight to EngramNode.working_memory_weight.
 *  11. Sort: promoted nodes (wm > 0) first by wm desc, then background-
 *      only by bg desc. Context compilation uses ONLY promoted nodes.
 *
 * Temporal decay:
 *   decay_factor = exp(-lambda * age_hours / T_half)
 *   T_half = 168.0 h (one week), lambda = ln(2)
 *
 * Activation dampening:
 *   dampen = 1.0 / (1.0 + log(1 + activation_count))
 *
 * engram_query_range(start_ms, end_ms):
 *   Returns nodes whose created_at OR last_activated falls within
 *   [start_ms, end_ms], sorted by created_at ascending.
 */

/* Temporal decay constants.
 * T_HALF_HOURS: half-life in hours — one week. After one week of no
 * activation a node retains 50% of its base salience contribution.
 * DECAY_LAMBDA: ln(2) ≈ 0.693147 */
#define ENGRAM_T_HALF_HOURS  168.0
#define ENGRAM_DECAY_LAMBDA  0.693147

/* Two-layer activation constants.
 * ENGRAM_WM_THRESHOLD: minimum background_activation for a node to be
 *   considered for working-memory promotion (layer 2 candidate gate).
 * ENGRAM_WM_DECAY: per-turn decay applied to working_memory_weight for
 *   nodes NOT re-activated in the current turn (conversational thread
 *   continuity: a node promoted in turn N persists with reduced weight
 *   into turn N+1 without re-activation cost).
 * ENGRAM_SUPPRESSION_BREAKTHROUGH: after this many consecutive suppressions
 *   a latent node forces itself into working memory at reduced weight,
 *   modelling the brain's "intrusive thought" / unresolved-tension surfacing.
 * ENGRAM_BREAKTHROUGH_WEIGHT: the reduced working_memory_weight assigned
 *   when a suppressed node breaks through.
 * ENGRAM_INHIBITION_FACTOR: multiplier applied to working_memory_weight when
 *   an inhibitory edge fires against a node (0 = full suppress, 0.3 = partial). */
#define ENGRAM_WM_THRESHOLD          0.15
#define ENGRAM_WM_DECAY              0.7
#define ENGRAM_SUPPRESSION_BREAKTHROUGH 5
#define ENGRAM_BREAKTHROUGH_WEIGHT   0.25
#define ENGRAM_INHIBITION_FACTOR     0.1

/* ── Layered consciousness architecture ──────────────────────────────────────
 *
 * The engram graph is stratified into LAYERS that gate which suppressions
 * apply during the executive filter pass. Layers are ordered shallow-to-deep
 * by `activation_priority`; the deepest layer (priority 0, conventionally
 * "safety") is the structural floor of the soul: nodes here cannot be
 * silenced by inhibitory edges from any other layer. Higher layers
 * (core-identity, domain-knowledge, imprint, suit) are normally
 * suppressible — they participate in attentional inhibition and goal
 * focus the way the prior single-graph implementation did.
 *
 * The five canonical layers (see engram_init_layers):
 *   0. safety          — structural, transparent, non-injectable, non-suppressible
 *   1. core-identity   — default for legacy nodes; suppressible
 *   2. domain-knowledge— suppressible
 *   3. imprint         — runtime-injectable (an Imprint package can add/remove)
 *   4. suit            — runtime-injectable (a Suit overlays domain skill)
 *
 * Three-pass activation (engram_activate):
 *   Pass 1 — Background fan-out: BFS spreads activation across ALL layers
 *            (existing behavior preserved). Inhibitory edges propagate at
 *            this layer too; no filtering happens here.
 *   Pass 2 — Working memory promotion: type-threshold gate, goal bias,
 *            confidence weighting, inhibitory suppression. Inhibitory edges
 *            ONLY apply against nodes whose layer is `suppressible == 1`.
 *            Nodes in non-suppressible layers (Layer 0) ignore inhibition.
 *   Pass 3 — Layer 0 override: every node in a non-suppressible layer that
 *            received background activation has its working_memory_weight
 *            forced to >= ENGRAM_LAYER0_OVERRIDE_WEIGHT. The sacred fire —
 *            safety nodes that touched any seed unconditionally surface,
 *            even when the executive filter would have silenced them.
 *
 * Layer fields:
 *   suppressible : 0 → inhibitory edges are ignored against nodes in this
 *                       layer during pass 2. Pass 3 also force-promotes them.
 *                  1 → standard behavior (most layers).
 *   transparent  : 1 → emitted into the prompt context so its content shapes
 *                       output, but filtered out of "what do you know about
 *                       yourself?" introspection queries (engram_search and
 *                       friends do not return transparent-layer nodes by
 *                       default). 0 → fully visible to introspection.
 *   injectable   : 1 → can be added/removed at runtime via engram_add_layer
 *                       and engram_remove_layer (imprints, suits).
 *                  0 → built-in, fixed at engram_get() initialization.
 *
 * Backward compatibility:
 *   Nodes and edges loaded from snapshots without a `layer_id` field default
 *   to layer 1 (core-identity). The five canonical layers are always present.
 */
#define ENGRAM_LAYER_SAFETY          0u
#define ENGRAM_LAYER_CORE_IDENTITY   1u
#define ENGRAM_LAYER_DOMAIN          2u
#define ENGRAM_LAYER_IMPRINT         3u
#define ENGRAM_LAYER_SUIT            4u
#define ENGRAM_LAYER_DEFAULT         ENGRAM_LAYER_CORE_IDENTITY

/* Pass 3 override floor. Layer 0 nodes that received any background
 * activation are force-promoted to AT LEAST this working_memory_weight,
 * regardless of inhibitory suppression in pass 2. */
#define ENGRAM_LAYER0_OVERRIDE_WEIGHT 1.0

/* Per-node-type activation thresholds.
 * Lower tier / safety-critical nodes fire more readily. */
static double engram_type_threshold(const char* node_type, const char* tier) {
    if (node_type) {
        if (strcmp(node_type, "DharmaSelf") == 0) return 0.05;
        if (strcmp(node_type, "Safety")     == 0) return 0.05;
    }
    if (tier) {
        if (strcmp(tier, "Canonical") == 0) return 0.15;
        if (strcmp(tier, "Lesson")    == 0) return 0.25;
    }
    if (node_type) {
        if (strcmp(node_type, "Belief") == 0) return 0.30;
        if (strcmp(node_type, "Entity") == 0) return 0.30;
    }
    return 0.40; /* Note / Memory / Working (most nodes) */
}

typedef struct EngramNode {
    char*   id;
    char*   content;
    char*   node_type;
    char*   label;
    char*   tier;
    char*   tags;
    char*   metadata;
    double  salience;
    double  importance;
    double  confidence;
    double  temporal_decay_rate; /* per-node override for lambda; 0 = use default */
    int64_t activation_count;
    int64_t last_activated;
    int64_t created_at;
    int64_t updated_at;
    /* Two-layer activation fields ─────────────────────────────────────────
     * background_activation: Layer 1. Set by BFS fan-out on every query.
     *   Every reachable node fires here — nothing is filtered at this stage.
     *   Models the brain's massive parallel sub-threshold activation of all
     *   associated content in response to a stimulus.
     * working_memory_weight: Layer 2. Executive filter output. Only nodes
     *   that survive goal-state / attentional-bias scoring receive a
     *   non-zero weight here. Context compilation ONLY uses this field.
     *   Background-activated nodes with working_memory_weight == 0 remain
     *   latent — real, available, but silent.
     * suppression_count: Consecutive turn count where this node was
     *   background-activated but NOT promoted to working memory. High
     *   values signal the node "wants to surface." After
     *   ENGRAM_SUPPRESSION_BREAKTHROUGH consecutive suppressions the node
     *   is force-promoted at a reduced weight (breakthrough activation). */
    double  background_activation;
    double  working_memory_weight;
    int32_t suppression_count;
    /* Layered consciousness — see ENGRAM_LAYER_* macros and engram_init_layers.
     * Defaults to ENGRAM_LAYER_DEFAULT (1, core-identity) for legacy nodes
     * created via engram_node / engram_node_full and for snapshots that
     * predate the layered schema. */
    uint32_t layer_id;
} EngramNode;

typedef struct EngramEdge {
    char*   id;
    char*   from_id;
    char*   to_id;
    char*   relation;
    char*   metadata;
    double  weight;
    double  confidence;
    int64_t created_at;
    int64_t updated_at;
    int64_t last_fired;
    /* Inhibitory flag: when 1, activating the source node SUPPRESSES the
     * working_memory_weight of the target node rather than exciting it.
     * Models attentional inhibition: "I am focused on code work" creates
     * inhibitory edges to personal/emotional nodes, preventing them from
     * surfacing even if they have high background_activation. */
    int     inhibitory;
    /* Layered consciousness — edges carry a layer assignment for
     * categorization/visualization. Pass 2 inhibitory gating is decided by
     * the TARGET node's layer (whether it's suppressible), not by the edge
     * layer. Defaults to ENGRAM_LAYER_DEFAULT. */
    uint32_t layer_id;
} EngramEdge;

/* Layered consciousness — runtime layer registry entry. */
typedef struct EngramLayer {
    uint32_t layer_id;             /* 0 = deepest (safety/limbic) */
    char*    name;                 /* persistent — owned by the store */
    uint32_t activation_priority;  /* lower = fires earlier; safety = 0 */
    int      suppressible;         /* can higher layers suppress nodes here? */
    int      transparent;          /* invisible to introspection queries? */
    int      injectable;           /* can be added/removed at runtime? */
} EngramLayer;

typedef struct EngramStore {
    EngramNode*  nodes;
    int64_t      node_count;
    int64_t      node_capacity;
    EngramEdge*  edges;
    int64_t      edge_count;
    int64_t      edge_capacity;
    /* Layer registry — see engram_init_layers. The five canonical layers
     * are always present; injectable layers (imprint, suit) are extended
     * via engram_add_layer at runtime. layer_id values are assigned
     * monotonically; removed injectable layers leave a NULL `name` slot
     * (tombstone) so existing layer_id references on nodes stay stable. */
    EngramLayer* layers;
    size_t       layer_count;
    size_t       layer_capacity;
} EngramStore;

static EngramStore* engram_global = NULL;

/* Initialize the five canonical layers on a fresh store. Called once from
 * engram_get(). Layer ids 0..4 are reserved; runtime-injected imprint/suit
 * layers (engram_add_layer) get ids 5+. */
static void engram_init_layers(EngramStore* g) {
    g->layer_capacity = 16;
    g->layers = calloc(g->layer_capacity, sizeof(EngramLayer));
    if (!g->layers) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    g->layer_count = 0;

    /* Layer 0 — safety. Structural floor. Non-suppressible; transparent
     * (filtered out of introspection but still shapes output); not
     * runtime-injectable. */
    g->layers[g->layer_count++] = (EngramLayer){
        .layer_id = ENGRAM_LAYER_SAFETY,
        .name = el_strdup_persist("safety"),
        .activation_priority = 0,
        .suppressible = 0,
        .transparent = 1,
        .injectable = 0
    };
    /* Layer 1 — core-identity. The default home for legacy nodes. */
    g->layers[g->layer_count++] = (EngramLayer){
        .layer_id = ENGRAM_LAYER_CORE_IDENTITY,
        .name = el_strdup_persist("core-identity"),
        .activation_priority = 10,
        .suppressible = 1,
        .transparent = 0,
        .injectable = 0
    };
    /* Layer 2 — domain-knowledge. */
    g->layers[g->layer_count++] = (EngramLayer){
        .layer_id = ENGRAM_LAYER_DOMAIN,
        .name = el_strdup_persist("domain-knowledge"),
        .activation_priority = 20,
        .suppressible = 1,
        .transparent = 0,
        .injectable = 0
    };
    /* Layer 3 — imprint. Injectable: an imprint package adds/removes this
     * layer (and the nodes assigned to it) as a unit. */
    g->layers[g->layer_count++] = (EngramLayer){
        .layer_id = ENGRAM_LAYER_IMPRINT,
        .name = el_strdup_persist("imprint"),
        .activation_priority = 30,
        .suppressible = 1,
        .transparent = 0,
        .injectable = 1
    };
    /* Layer 4 — suit. Injectable: a Suit overlays domain skill (e.g.
     * "enterprise advisor", "divorce lawyer") and can be detached. */
    g->layers[g->layer_count++] = (EngramLayer){
        .layer_id = ENGRAM_LAYER_SUIT,
        .name = el_strdup_persist("suit"),
        .activation_priority = 40,
        .suppressible = 1,
        .transparent = 0,
        .injectable = 1
    };
}

static EngramStore* engram_get(void) {
    if (engram_global) return engram_global;
    engram_global = calloc(1, sizeof(EngramStore));
    if (!engram_global) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    engram_global->node_capacity = 16;
    engram_global->nodes = calloc((size_t)engram_global->node_capacity, sizeof(EngramNode));
    engram_global->edge_capacity = 16;
    engram_global->edges = calloc((size_t)engram_global->edge_capacity, sizeof(EngramEdge));
    engram_init_layers(engram_global);
    return engram_global;
}

/* Resolve a layer record by id. Returns NULL if no layer with that id
 * exists (e.g. a removed injectable layer or a malformed snapshot). */
static EngramLayer* engram_find_layer(uint32_t layer_id) {
    EngramStore* g = engram_get();
    for (size_t i = 0; i < g->layer_count; i++) {
        EngramLayer* L = &g->layers[i];
        if (!L->name) continue; /* tombstone for removed injectable layer */
        if (L->layer_id == layer_id) return L;
    }
    return NULL;
}

/* Resolve a layer record by name. Returns NULL if not found. */
static EngramLayer* engram_find_layer_by_name(const char* name) {
    if (!name || !*name) return NULL;
    EngramStore* g = engram_get();
    for (size_t i = 0; i < g->layer_count; i++) {
        EngramLayer* L = &g->layers[i];
        if (!L->name) continue;
        if (strcmp(L->name, name) == 0) return L;
    }
    return NULL;
}

/* Allocate the next layer id. Skips ids that are still in use. */
static uint32_t engram_next_layer_id(void) {
    EngramStore* g = engram_get();
    uint32_t maxid = 0;
    for (size_t i = 0; i < g->layer_count; i++) {
        if (g->layers[i].layer_id > maxid) maxid = g->layers[i].layer_id;
    }
    return maxid + 1;
}

/* Whether a node in `layer_id` may be silenced by inhibitory edges in pass 2. */
static int engram_layer_is_suppressible(uint32_t layer_id) {
    EngramLayer* L = engram_find_layer(layer_id);
    if (!L) return 1; /* unknown layer → safe default: standard suppression */
    return L->suppressible ? 1 : 0;
}

/* Whether a layer is transparent (its content shapes output but is filtered
 * from introspection queries). Currently used to mark Layer 0 as invisible
 * to "what do you know about yourself" lookups while still letting it
 * dominate the prompt context. */
static int engram_layer_is_transparent(uint32_t layer_id) {
    EngramLayer* L = engram_find_layer(layer_id);
    if (!L) return 0;
    return L->transparent ? 1 : 0;
}

static int64_t engram_now_ms(void) {
    struct timeval tv; gettimeofday(&tv, NULL);
    return (int64_t)tv.tv_sec * 1000LL + (int64_t)tv.tv_usec / 1000LL;
}

static EngramNode* engram_find_node(const char* id) {
    if (!id) return NULL;
    EngramStore* g = engram_get();
    for (int64_t i = 0; i < g->node_count; i++) {
        if (g->nodes[i].id && strcmp(g->nodes[i].id, id) == 0) return &g->nodes[i];
    }
    return NULL;
}

static int64_t engram_find_node_index(const char* id) {
    if (!id) return -1;
    EngramStore* g = engram_get();
    for (int64_t i = 0; i < g->node_count; i++) {
        if (g->nodes[i].id && strcmp(g->nodes[i].id, id) == 0) return i;
    }
    return -1;
}

static void engram_grow_nodes(void) {
    EngramStore* g = engram_get();
    if (g->node_count < g->node_capacity) return;
    int64_t nc = g->node_capacity * 2;
    g->nodes = realloc(g->nodes, (size_t)nc * sizeof(EngramNode));
    if (!g->nodes) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    memset(g->nodes + g->node_capacity, 0,
           (size_t)(nc - g->node_capacity) * sizeof(EngramNode));
    g->node_capacity = nc;
}

static void engram_grow_edges(void) {
    EngramStore* g = engram_get();
    if (g->edge_count < g->edge_capacity) return;
    int64_t nc = g->edge_capacity * 2;
    g->edges = realloc(g->edges, (size_t)nc * sizeof(EngramEdge));
    if (!g->edges) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
    memset(g->edges + g->edge_capacity, 0,
           (size_t)(nc - g->edge_capacity) * sizeof(EngramEdge));
    g->edge_capacity = nc;
}

/* Build a fresh UUID string. Reuses uuid_new but takes the underlying char*. */
static char* engram_new_id(void) {
    el_val_t v = uuid_new();
    const char* s = EL_CSTR(v);
    return el_strdup(s ? s : "");
}

/* Convert a node into an ElMap of its fields.                            */
static el_val_t engram_node_to_map(const EngramNode* n) {
    el_val_t m = el_map_new(0);
    m = el_map_set(m, EL_STR(el_strdup("id")),         EL_STR(el_strdup(n->id ? n->id : "")));
    m = el_map_set(m, EL_STR(el_strdup("content")),    EL_STR(el_strdup(n->content ? n->content : "")));
    m = el_map_set(m, EL_STR(el_strdup("node_type")),  EL_STR(el_strdup(n->node_type ? n->node_type : "")));
    m = el_map_set(m, EL_STR(el_strdup("label")),      EL_STR(el_strdup(n->label ? n->label : "")));
    m = el_map_set(m, EL_STR(el_strdup("tier")),       EL_STR(el_strdup(n->tier ? n->tier : "Working")));
    m = el_map_set(m, EL_STR(el_strdup("tags")),       EL_STR(el_strdup(n->tags ? n->tags : "")));
    m = el_map_set(m, EL_STR(el_strdup("metadata")),   EL_STR(el_strdup(n->metadata ? n->metadata : "{}")));
    m = el_map_set(m, EL_STR(el_strdup("salience")),            el_from_float(n->salience));
    m = el_map_set(m, EL_STR(el_strdup("importance")),           el_from_float(n->importance));
    m = el_map_set(m, EL_STR(el_strdup("confidence")),           el_from_float(n->confidence));
    m = el_map_set(m, EL_STR(el_strdup("temporal_decay_rate")),   el_from_float(n->temporal_decay_rate));
    m = el_map_set(m, EL_STR(el_strdup("activation_count")),      (el_val_t)n->activation_count);
    m = el_map_set(m, EL_STR(el_strdup("last_activated")),        (el_val_t)n->last_activated);
    m = el_map_set(m, EL_STR(el_strdup("created_at")),            (el_val_t)n->created_at);
    m = el_map_set(m, EL_STR(el_strdup("updated_at")),            (el_val_t)n->updated_at);
    m = el_map_set(m, EL_STR(el_strdup("background_activation")), el_from_float(n->background_activation));
    m = el_map_set(m, EL_STR(el_strdup("working_memory_weight")), el_from_float(n->working_memory_weight));
    m = el_map_set(m, EL_STR(el_strdup("suppression_count")),     (el_val_t)n->suppression_count);
    m = el_map_set(m, EL_STR(el_strdup("layer_id")),              (el_val_t)(int64_t)n->layer_id);
    return m;
}

/* (Node JSON serialization is provided by `engram_emit_node_json` further
 * down in the persistence section — reused by the *_json builtins below.) */
static void engram_emit_node_json(JsonBuf* b, const EngramNode* n);
static void engram_emit_edge_json(JsonBuf* b, const EngramEdge* e);

/* Salience may arrive either as a float bit-pattern or as a small integer
 * (e.g. 1, meaning 1.0). Heuristic: if interpreted as double it's in
 * [0.0, 100.0] use it; otherwise treat as int and convert. */
static double engram_decode_score(el_val_t v) {
    double f = el_to_float(v);
    if (!isnan(f) && !isinf(f) && f >= 0.0 && f <= 100.0) return f;
    int64_t n = (int64_t)v;
    return (double)n;
}

static char* engram_first_n_chars(const char* s, size_t n) {
    if (!s) return el_strdup("");
    size_t l = strlen(s);
    if (l > n) l = n;
    char* out = el_strbuf(l);
    memcpy(out, s, l);
    out[l] = '\0';
    return out;
}

el_val_t engram_node(el_val_t content, el_val_t node_type, el_val_t salience) {
    EngramStore* g = engram_get();
    engram_grow_nodes();
    EngramNode* n = &g->nodes[g->node_count];
    memset(n, 0, sizeof(*n));
    n->id        = engram_new_id();
    const char* c  = EL_CSTR(content);
    const char* nt = EL_CSTR(node_type);
    n->content   = el_strdup(c ? c : "");
    n->node_type = el_strdup(nt && *nt ? nt : "Memory");
    n->label     = engram_first_n_chars(c, 60);
    n->tier      = el_strdup("Working");
    n->tags      = el_strdup("");
    n->metadata  = el_strdup("{}");
    n->salience    = engram_decode_score(salience);
    if (n->salience <= 0.0 || n->salience > 1.0) n->salience = 0.5;
    n->importance  = 0.5;
    n->confidence  = 1.0;
    n->temporal_decay_rate = 0.0; /* 0 = use global default ENGRAM_DECAY_LAMBDA */
    n->activation_count = 0;
    int64_t now = engram_now_ms();
    n->last_activated = now;
    n->created_at = now;
    n->updated_at = now;
    n->layer_id   = ENGRAM_LAYER_DEFAULT;
    g->node_count++;
    return el_wrap_str(el_strdup(n->id));
}

el_val_t engram_node_full(el_val_t content, el_val_t node_type, el_val_t label,
                          el_val_t salience, el_val_t importance, el_val_t confidence,
                          el_val_t tier, el_val_t tags) {
    EngramStore* g = engram_get();
    engram_grow_nodes();
    EngramNode* n = &g->nodes[g->node_count];
    memset(n, 0, sizeof(*n));
    n->id        = engram_new_id();
    const char* c  = EL_CSTR(content);
    const char* nt = EL_CSTR(node_type);
    const char* lb = EL_CSTR(label);
    const char* ti = EL_CSTR(tier);
    const char* tg = EL_CSTR(tags);
    n->content   = el_strdup(c ? c : "");
    n->node_type = el_strdup(nt && *nt ? nt : "Memory");
    n->label     = el_strdup(lb && *lb ? lb : (c ? engram_first_n_chars(c, 60) : ""));
    n->tier      = el_strdup(ti && *ti ? ti : "Working");
    n->tags      = el_strdup(tg ? tg : "");
    n->metadata  = el_strdup("{}");
    n->salience    = engram_decode_score(salience);
    n->importance  = engram_decode_score(importance);
    n->confidence  = engram_decode_score(confidence);
    if (n->salience    <= 0.0 || n->salience    > 1.0) n->salience    = 0.5;
    if (n->importance  <= 0.0 || n->importance  > 1.0) n->importance  = 0.5;
    if (n->confidence  <= 0.0 || n->confidence  > 1.0) n->confidence  = 1.0;
    n->temporal_decay_rate = 0.0; /* 0 = use global default ENGRAM_DECAY_LAMBDA */
    n->activation_count = 0;
    int64_t now = engram_now_ms();
    n->last_activated = now;
    n->created_at = now;
    n->updated_at = now;
    n->layer_id   = ENGRAM_LAYER_DEFAULT;
    g->node_count++;
    return el_wrap_str(el_strdup(n->id));
}

/* engram_node_layered — like engram_node_full but with explicit layer
 * assignment and an additional `status` slot reserved for callers that
 * track lifecycle state in metadata. The signature mirrors the public API
 * defined in the layered consciousness design doc:
 *
 *   engram_node_layered(content, node_type, label,
 *                       salience, certainty, confidence,
 *                       status, tags, layer_id)
 *
 * `certainty` is folded into `importance` (it occupies the same axis in
 * the existing schema). `status` is recorded under metadata.status; an
 * empty status leaves metadata as the default "{}".
 *
 * If `layer_id` does not resolve to a known layer the call falls back to
 * ENGRAM_LAYER_DEFAULT — better to keep the node addressable than to drop
 * it because of a stale layer reference. Callers wanting strict validation
 * should engram_list_layers first. */
el_val_t engram_node_layered(el_val_t content, el_val_t node_type, el_val_t label,
                             el_val_t salience, el_val_t certainty, el_val_t confidence,
                             el_val_t status, el_val_t tags, el_val_t layer_id) {
    EngramStore* g = engram_get();
    engram_grow_nodes();
    EngramNode* n = &g->nodes[g->node_count];
    memset(n, 0, sizeof(*n));
    n->id        = engram_new_id();
    const char* c  = EL_CSTR(content);
    const char* nt = EL_CSTR(node_type);
    const char* lb = EL_CSTR(label);
    const char* tg = EL_CSTR(tags);
    const char* st = EL_CSTR(status);
    n->content   = el_strdup(c ? c : "");
    n->node_type = el_strdup(nt && *nt ? nt : "Memory");
    n->label     = el_strdup(lb && *lb ? lb : (c ? engram_first_n_chars(c, 60) : ""));
    n->tier      = el_strdup("Working");
    n->tags      = el_strdup(tg ? tg : "");
    if (st && *st) {
        /* Minimal metadata payload: {"status":"..."}. Keep it cheap so
         * callers using `status` don't pay JSON parse cost on every read. */
        size_t sl = strlen(st) + 16;
        char* meta = el_strbuf(sl);
        snprintf(meta, sl, "{\"status\":\"%s\"}", st);
        n->metadata = meta;
    } else {
        n->metadata = el_strdup("{}");
    }
    n->salience    = engram_decode_score(salience);
    n->importance  = engram_decode_score(certainty);
    n->confidence  = engram_decode_score(confidence);
    if (n->salience    <= 0.0 || n->salience    > 1.0) n->salience    = 0.5;
    if (n->importance  <= 0.0 || n->importance  > 1.0) n->importance  = 0.5;
    if (n->confidence  <= 0.0 || n->confidence  > 1.0) n->confidence  = 1.0;
    n->temporal_decay_rate = 0.0;
    n->activation_count = 0;
    int64_t now = engram_now_ms();
    n->last_activated = now;
    n->created_at = now;
    n->updated_at = now;
    /* Resolve layer assignment. Caller passes either a numeric layer_id or
     * a stringified id; el_to_float / int cast tolerates both. */
    int64_t lid = (int64_t)layer_id;
    if (lid < 0) lid = (int64_t)ENGRAM_LAYER_DEFAULT;
    if (!engram_find_layer((uint32_t)lid)) lid = (int64_t)ENGRAM_LAYER_DEFAULT;
    n->layer_id = (uint32_t)lid;
    g->node_count++;
    return el_wrap_str(el_strdup(n->id));
}

/* ── Layer registry public API ──────────────────────────────────────────────
 *
 * The five canonical layers are seeded at engram_get() initialization.
 * Runtime code (typically imprint/suit injection logic at the EL level)
 * can extend the registry with engram_add_layer() — only layers marked
 * `injectable=1` may be removed via engram_remove_layer(). Removing a
 * layer leaves a tombstone slot so existing layer_id references on nodes
 * stay valid; orphaned references resolve to "unknown layer" and inherit
 * the default suppression behavior.
 */

/* engram_add_layer — register a new layer at runtime.
 * Returns the assigned layer_id as an el_val_t int (cast back via int64_t).
 * Conflicting names are rejected (returns 0). */
el_val_t engram_add_layer(el_val_t name, el_val_t priority, el_val_t suppressible,
                          el_val_t transparent, el_val_t injectable) {
    EngramStore* g = engram_get();
    const char* nm = EL_CSTR(name);
    if (!nm || !*nm) return (el_val_t)0;
    if (engram_find_layer_by_name(nm)) {
        /* Name collision — return existing id so callers are idempotent. */
        return (el_val_t)(int64_t)engram_find_layer_by_name(nm)->layer_id;
    }
    if (g->layer_count >= g->layer_capacity) {
        size_t nc = g->layer_capacity ? g->layer_capacity * 2 : 16;
        EngramLayer* grown = realloc(g->layers, nc * sizeof(EngramLayer));
        if (!grown) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
        memset(grown + g->layer_capacity, 0,
               (nc - g->layer_capacity) * sizeof(EngramLayer));
        g->layers = grown;
        g->layer_capacity = nc;
    }
    EngramLayer* L = &g->layers[g->layer_count++];
    L->layer_id            = engram_next_layer_id();
    L->name                = el_strdup_persist(nm);
    L->activation_priority = (uint32_t)(int64_t)priority;
    L->suppressible        = (int)(int64_t)suppressible ? 1 : 0;
    L->transparent         = (int)(int64_t)transparent ? 1 : 0;
    L->injectable          = (int)(int64_t)injectable  ? 1 : 0;
    return (el_val_t)(int64_t)L->layer_id;
}

/* engram_remove_layer — remove an injectable layer by id.
 * Built-in (non-injectable) layers cannot be removed. Nodes still tagged
 * with the removed layer's id keep their tag but resolve to "unknown
 * layer" thereafter and inherit standard (suppressible) behavior.
 * Returns 1 on success, 0 on failure (unknown id, non-injectable). */
el_val_t engram_remove_layer(el_val_t layer_id) {
    EngramStore* g = engram_get();
    int64_t lid = (int64_t)layer_id;
    for (size_t i = 0; i < g->layer_count; i++) {
        EngramLayer* L = &g->layers[i];
        if (!L->name) continue;
        if ((int64_t)L->layer_id != lid) continue;
        if (!L->injectable) return (el_val_t)0;
        free(L->name);
        L->name = NULL; /* tombstone */
        /* Leave layer_id, priority, flags intact so debug snapshots can
         * still distinguish "removed at runtime" from "never existed". */
        return (el_val_t)1;
    }
    return (el_val_t)0;
}

/* engram_list_layers — enumerate the active layer registry.
 * Returns an ElList of maps, one per non-tombstone layer, sorted by
 * activation_priority ascending (deepest layer first). */
el_val_t engram_list_layers(void) {
    EngramStore* g = engram_get();
    el_val_t lst = el_list_empty();
    if (g->layer_count == 0) return lst;
    /* Build an index sorted by activation_priority ascending. */
    size_t* idx = malloc(g->layer_count * sizeof(size_t));
    if (!idx) return lst;
    size_t live = 0;
    for (size_t i = 0; i < g->layer_count; i++) {
        if (g->layers[i].name) idx[live++] = i;
    }
    /* Insertion sort — N is small (≤ a few dozen layers). */
    for (size_t i = 1; i < live; i++) {
        size_t key = idx[i];
        uint32_t kp = g->layers[key].activation_priority;
        size_t j = i;
        while (j > 0 && g->layers[idx[j - 1]].activation_priority > kp) {
            idx[j] = idx[j - 1];
            j--;
        }
        idx[j] = key;
    }
    for (size_t i = 0; i < live; i++) {
        EngramLayer* L = &g->layers[idx[i]];
        el_val_t m = el_map_new(0);
        m = el_map_set(m, EL_STR(el_strdup("layer_id")),
                       (el_val_t)(int64_t)L->layer_id);
        m = el_map_set(m, EL_STR(el_strdup("name")),
                       EL_STR(el_strdup(L->name ? L->name : "")));
        m = el_map_set(m, EL_STR(el_strdup("activation_priority")),
                       (el_val_t)(int64_t)L->activation_priority);
        m = el_map_set(m, EL_STR(el_strdup("suppressible")),
                       (el_val_t)(int64_t)(L->suppressible ? 1 : 0));
        m = el_map_set(m, EL_STR(el_strdup("transparent")),
                       (el_val_t)(int64_t)(L->transparent ? 1 : 0));
        m = el_map_set(m, EL_STR(el_strdup("injectable")),
                       (el_val_t)(int64_t)(L->injectable ? 1 : 0));
        lst = el_list_append(lst, m);
    }
    free(idx);
    return lst;
}

el_val_t engram_get_node(el_val_t id) {
    const char* sid = EL_CSTR(id);
    EngramNode* n = engram_find_node(sid);
    if (!n) return el_map_new(0);
    return engram_node_to_map(n);
}

void engram_strengthen(el_val_t node_id) {
    const char* sid = EL_CSTR(node_id);
    EngramNode* n = engram_find_node(sid);
    if (!n) return;
    n->salience += 0.05;
    if (n->salience > 1.0) n->salience = 1.0;
    n->activation_count++;
    n->last_activated = engram_now_ms();
    n->updated_at = n->last_activated;
}

void engram_forget(el_val_t node_id) {
    const char* sid = EL_CSTR(node_id);
    if (!sid) return;
    EngramStore* g = engram_get();
    int64_t idx = engram_find_node_index(sid);
    if (idx < 0) return;
    /* Free node strings */
    EngramNode* n = &g->nodes[idx];
    free(n->id); free(n->content); free(n->node_type); free(n->label);
    free(n->tier); free(n->tags); free(n->metadata);
    /* Shift remaining nodes down */
    for (int64_t i = idx + 1; i < g->node_count; i++) {
        g->nodes[i - 1] = g->nodes[i];
    }
    g->node_count--;
    memset(&g->nodes[g->node_count], 0, sizeof(EngramNode));
    /* Remove all incident edges */
    int64_t w = 0;
    for (int64_t r = 0; r < g->edge_count; r++) {
        EngramEdge* e = &g->edges[r];
        int incident = (e->from_id && strcmp(e->from_id, sid) == 0) ||
                       (e->to_id   && strcmp(e->to_id,   sid) == 0);
        if (incident) {
            free(e->id); free(e->from_id); free(e->to_id);
            free(e->relation); free(e->metadata);
        } else {
            if (w != r) g->edges[w] = g->edges[r];
            w++;
        }
    }
    g->edge_count = w;
}

el_val_t engram_node_count(void) {
    return (el_val_t)engram_get()->node_count;
}

static int istr_contains(const char* hay, const char* needle) {
    if (!hay || !needle || !*needle) return 0;
    size_t nl = strlen(needle);
    for (const char* p = hay; *p; p++) {
        if (strncasecmp(p, needle, nl) == 0) return 1;
    }
    return 0;
}

el_val_t engram_search(el_val_t query, el_val_t limit) {
    EngramStore* g = engram_get();
    const char* q = EL_CSTR(query);
    int64_t lim = (int64_t)limit;
    if (lim <= 0) lim = 100;
    el_val_t lst = el_list_empty();
    if (!q || !*q) return lst;
    int64_t found = 0;
    for (int64_t i = 0; i < g->node_count && found < lim; i++) {
        EngramNode* n = &g->nodes[i];
        /* Filter transparent layers: nodes whose layer is `transparent=1`
         * shape output but are invisible to introspection ("what do you
         * know about yourself"). They still surface via engram_activate
         * + engram_compile_layered_json — that's the legitimate path. */
        if (engram_layer_is_transparent(n->layer_id)) continue;
        if (istr_contains(n->content, q) ||
            istr_contains(n->label,   q) ||
            istr_contains(n->tags,    q)) {
            lst = el_list_append(lst, engram_node_to_map(n));
            found++;
        }
    }
    return lst;
}

/* Sort node indices by salience desc (small N, insertion sort is fine). */
static void engram_sort_indices_by_salience(int64_t* arr, int64_t n,
                                             const EngramNode* nodes) {
    for (int64_t i = 1; i < n; i++) {
        int64_t key = arr[i];
        double  ks  = nodes[key].salience;
        int64_t j = i - 1;
        while (j >= 0 && nodes[arr[j]].salience < ks) {
            arr[j + 1] = arr[j];
            j--;
        }
        arr[j + 1] = key;
    }
}

el_val_t engram_scan_nodes(el_val_t limit, el_val_t offset) {
    EngramStore* g = engram_get();
    int64_t lim = (int64_t)limit; if (lim <= 0) lim = 100;
    int64_t off = (int64_t)offset; if (off < 0) off = 0;
    el_val_t lst = el_list_empty();
    if (g->node_count == 0) return lst;
    int64_t* idx = malloc((size_t)g->node_count * sizeof(int64_t));
    if (!idx) return lst;
    /* Skip transparent layers — same introspection-filter rationale as
     * engram_search above. */
    int64_t live = 0;
    for (int64_t i = 0; i < g->node_count; i++) {
        if (engram_layer_is_transparent(g->nodes[i].layer_id)) continue;
        idx[live++] = i;
    }
    engram_sort_indices_by_salience(idx, live, g->nodes);
    int64_t end = off + lim;
    if (end > live) end = live;
    for (int64_t i = off; i < end; i++) {
        lst = el_list_append(lst, engram_node_to_map(&g->nodes[idx[i]]));
    }
    free(idx);
    return lst;
}

void engram_connect(el_val_t from_id, el_val_t to_id, el_val_t weight, el_val_t relation) {
    EngramStore* g = engram_get();
    const char* f = EL_CSTR(from_id);
    const char* t = EL_CSTR(to_id);
    const char* r = EL_CSTR(relation);
    if (!f || !t) return;
    engram_grow_edges();
    EngramEdge* e = &g->edges[g->edge_count];
    memset(e, 0, sizeof(*e));
    e->id        = engram_new_id();
    e->from_id   = el_strdup(f);
    e->to_id     = el_strdup(t);
    e->relation  = el_strdup(r && *r ? r : "associate");
    e->metadata  = el_strdup("{}");
    e->weight    = engram_decode_score(weight);
    if (e->weight <= 0.0 || e->weight > 1.0) e->weight = 0.5;
    e->confidence = 1.0;
    int64_t now = engram_now_ms();
    e->created_at = now;
    e->updated_at = now;
    e->last_fired = 0;
    e->layer_id   = ENGRAM_LAYER_DEFAULT;
    g->edge_count++;
}

el_val_t engram_edge_between(el_val_t from_id, el_val_t to_id) {
    EngramStore* g = engram_get();
    const char* f = EL_CSTR(from_id);
    const char* t = EL_CSTR(to_id);
    if (!f || !t) return 0;
    for (int64_t i = 0; i < g->edge_count; i++) {
        EngramEdge* e = &g->edges[i];
        if (e->from_id && e->to_id &&
            strcmp(e->from_id, f) == 0 && strcmp(e->to_id, t) == 0) return 1;
    }
    return 0;
}

/* Reserved helper: edge -> ElMap. Kept around for future builtins.       */
static el_val_t engram_edge_to_map(const EngramEdge* e) __attribute__((unused));
static el_val_t engram_edge_to_map(const EngramEdge* e) {
    el_val_t m = el_map_new(0);
    m = el_map_set(m, EL_STR(el_strdup("id")),         EL_STR(el_strdup(e->id ? e->id : "")));
    m = el_map_set(m, EL_STR(el_strdup("from_id")),    EL_STR(el_strdup(e->from_id ? e->from_id : "")));
    m = el_map_set(m, EL_STR(el_strdup("to_id")),      EL_STR(el_strdup(e->to_id ? e->to_id : "")));
    m = el_map_set(m, EL_STR(el_strdup("relation")),   EL_STR(el_strdup(e->relation ? e->relation : "")));
    m = el_map_set(m, EL_STR(el_strdup("metadata")),   EL_STR(el_strdup(e->metadata ? e->metadata : "{}")));
    m = el_map_set(m, EL_STR(el_strdup("weight")),     el_from_float(e->weight));
    m = el_map_set(m, EL_STR(el_strdup("confidence")), el_from_float(e->confidence));
    m = el_map_set(m, EL_STR(el_strdup("created_at")), (el_val_t)e->created_at);
    m = el_map_set(m, EL_STR(el_strdup("updated_at")), (el_val_t)e->updated_at);
    m = el_map_set(m, EL_STR(el_strdup("last_fired")), (el_val_t)e->last_fired);
    m = el_map_set(m, EL_STR(el_strdup("inhibitory")), (el_val_t)(e->inhibitory ? 1 : 0));
    m = el_map_set(m, EL_STR(el_strdup("layer_id")),   (el_val_t)(int64_t)e->layer_id);
    return m;
}

el_val_t engram_neighbors(el_val_t node_id) {
    EngramStore* g = engram_get();
    const char* sid = EL_CSTR(node_id);
    el_val_t lst = el_list_empty();
    if (!sid) return lst;
    for (int64_t i = 0; i < g->edge_count; i++) {
        EngramEdge* e = &g->edges[i];
        const char* other = NULL;
        if (e->from_id && strcmp(e->from_id, sid) == 0) other = e->to_id;
        else if (e->to_id && strcmp(e->to_id, sid) == 0) other = e->from_id;
        if (!other) continue;
        EngramNode* n = engram_find_node(other);
        if (n) lst = el_list_append(lst, engram_node_to_map(n));
    }
    return lst;
}

el_val_t engram_neighbors_filtered(el_val_t node_id, el_val_t max_depth, el_val_t direction) {
    EngramStore* g = engram_get();
    const char* sid = EL_CSTR(node_id);
    int64_t md = (int64_t)max_depth; if (md <= 0) md = 1;
    const char* dir = EL_CSTR(direction); /* "out" | "in" | "both" (default) */
    el_val_t lst = el_list_empty();
    if (!sid || g->node_count == 0) return lst;
    int64_t start = engram_find_node_index(sid);
    if (start < 0) return lst;
    /* BFS with depth tracking */
    int64_t* visited = calloc((size_t)g->node_count, sizeof(int64_t));
    int64_t* queue   = calloc((size_t)g->node_count, sizeof(int64_t));
    int64_t* depths  = calloc((size_t)g->node_count, sizeof(int64_t));
    if (!visited || !queue || !depths) {
        free(visited); free(queue); free(depths); return lst;
    }
    int64_t qh = 0, qt = 0;
    queue[qt++] = start;
    visited[start] = 1;
    depths[start] = 0;
    while (qh < qt) {
        int64_t cur = queue[qh++];
        const char* cur_id = g->nodes[cur].id;
        int64_t cur_depth = depths[cur];
        if (cur_depth >= md) continue;
        for (int64_t i = 0; i < g->edge_count; i++) {
            EngramEdge* e = &g->edges[i];
            const char* other = NULL;
            int outgoing = e->from_id && strcmp(e->from_id, cur_id) == 0;
            int incoming = e->to_id   && strcmp(e->to_id,   cur_id) == 0;
            if (dir && strcmp(dir, "out") == 0 && !outgoing) continue;
            if (dir && strcmp(dir, "in")  == 0 && !incoming) continue;
            if (outgoing) other = e->to_id;
            else if (incoming) other = e->from_id;
            else continue;
            int64_t oi = engram_find_node_index(other);
            if (oi < 0 || visited[oi]) continue;
            visited[oi] = 1;
            depths[oi]  = cur_depth + 1;
            queue[qt++] = oi;
        }
    }
    /* Emit all visited except the seed */
    for (int64_t i = 0; i < g->node_count; i++) {
        if (visited[i] && i != start) {
            lst = el_list_append(lst, engram_node_to_map(&g->nodes[i]));
        }
    }
    free(visited); free(queue); free(depths);
    return lst;
}

el_val_t engram_edge_count(void) {
    return (el_val_t)engram_get()->edge_count;
}

/* Compute temporal decay factor for a node given current time.
 * effective contribution = salience * exp(-lambda * age_hours / T_half)
 * Clamped to [0.05, 1.0] so very old nodes retain a meaningful floor. */
static double engram_temporal_decay(const EngramNode* n, int64_t now_ms) {
    int64_t age_ms = now_ms - n->last_activated;
    if (age_ms <= 0) return 1.0;
    double lambda = (n->temporal_decay_rate > 0.0) ? n->temporal_decay_rate
                                                    : ENGRAM_DECAY_LAMBDA;
    double age_hours = (double)age_ms / 3600000.0;
    double factor = exp(-lambda * age_hours / ENGRAM_T_HALF_HOURS);
    if (factor < 0.05) factor = 0.05;
    return factor;
}

/* Activation dampening: high activation_count nodes are "well-known" context
 * and get less marginal boost per firing.
 * count=0 → 1.0, count=2 → ~0.74, count=9 → ~0.59, count=99 → ~0.43 */
static double engram_activation_dampen(const EngramNode* n) {
    return 1.0 / (1.0 + log(1.0 + (double)n->activation_count));
}

/* Temporal proximity bonus: boost propagation along edges connecting
 * co-temporal nodes. Returns a multiplier bonus in [0, 0.2]. */
static double engram_temporal_proximity_bonus(int64_t node_created,
                                               int64_t seed_epoch) {
    int64_t diff = node_created - seed_epoch;
    if (diff < 0) diff = -diff;
    if (diff < 86400000LL)    return 0.20; /* within 1 day  */
    if (diff < 604800000LL)   return 0.10; /* within 7 days */
    return 0.0;
}

/* ── Two-layer activation (biologically-motivated) ───────────────────────────
 *
 * Layer 1 — Broad fan-out (background activation):
 *   BFS + spreading activation fires on ALL nodes reachable from seeds,
 *   regardless of relevance to the current goal. Every reachable node gets
 *   a background_activation score. Nothing is filtered here. Models the
 *   brain's massive parallel sub-threshold activation of all associated
 *   content in response to a stimulus. Temporal decay and activation
 *   dampening are applied at this layer (as before), but no threshold gate.
 *
 * Layer 2 — Executive filter (working memory promotion):
 *   A second pass asks: given the query (goal intent), attentional bias,
 *   and inhibitory edge topology — which background-activated nodes should
 *   break through into working memory?
 *
 *     wm_weight = bg_activation * goal_bias(node, query) * confidence
 *                 * inhibitory_suppression_factor
 *
 *   Only nodes where wm_weight >= ENGRAM_WM_THRESHOLD are promoted to
 *   working memory (working_memory_weight > 0). Background-activated nodes
 *   that don't cross the threshold accumulate suppression_count. After
 *   ENGRAM_SUPPRESSION_BREAKTHROUGH consecutive suppressed turns, the node
 *   force-breaks through at ENGRAM_BREAKTHROUGH_WEIGHT (latent tension
 *   surfacing — models intrusive memory / unresolved cognitive load).
 *
 * Inhibitory edges:
 *   An edge with inhibitory=1 suppresses the TARGET node's working memory
 *   promotion when the SOURCE is background-activated. Background activation
 *   of the target is NOT affected — the node fires in layer 1. Only the
 *   executive filter (layer 2) is gated. Models attentional inhibition:
 *   "focused on code work" suppresses personal memories from surfacing
 *   even if they have high background_activation.
 *
 * Goal bias:
 *   A lightweight heuristic rates how well each background-activated node
 *   aligns with the apparent intent of the current query. Technical queries
 *   boost Belief/Canonical/Lesson nodes; relational queries boost Memory/
 *   Entity nodes. Direct lexical overlap gives a 50% bonus.
 *
 * Working memory persistence (turn continuity):
 *   Nodes promoted in the previous turn retain a decayed working_memory_weight
 *   (weight *= ENGRAM_WM_DECAY) without needing re-activation. This models
 *   conversational thread continuity — once a topic is in working memory,
 *   it persists slightly into the next turn.
 *
 * Returns ElList of {node, activation_strength, working_memory_weight,
 *   epistemic_confidence, hops, promoted}.
 * "promoted" = 1 if working_memory_weight > 0, 0 if background-only.
 * Context compilation uses ONLY nodes with promoted=1.
 *
 * Temporal decay (preserved from prior implementation):
 *   effective_salience = salience * exp(-lambda * age_hours / T_half)
 *   where T_half = 168 h (one week), lambda = ln(2)
 *
 * Activation dampening (preserved):
 *   dampen = 1 / (1 + log(1 + activation_count))
 *
 * Temporal proximity bonus (preserved):
 *   edge_strength *= (1 + tbonus) where tbonus ∈ {0, 0.10, 0.20}
 *
 * Per-type threshold gates apply only to working memory promotion (layer 2):
 *   Safety/DharmaSelf: 0.05  Canonical: 0.15  Lesson: 0.25
 *   Belief/Entity: 0.30      Note/Memory/Working: 0.40
 */

/* Compute goal-state bias multiplier for a node given the query.
 * Returns a value in [0.3, 2.0]. This is a lightweight heuristic —
 * a production implementation may use LLM-derived intent classification. */
static double engram_goal_bias(const EngramNode* n, const char* query) {
    if (!query || !*query) return 1.0;
    double bias = 1.0;
    /* Direct lexical overlap: node content/label/tags share text with query. */
    if (istr_contains(n->content, query) || istr_contains(n->label, query) ||
        istr_contains(n->tags, query)) {
        bias += 0.5;
    }
    /* Node-type resonance with query intent. */
    int technical_query = istr_contains(query, "code")         ||
                          istr_contains(query, "function")     ||
                          istr_contains(query, "implement")    ||
                          istr_contains(query, "error")        ||
                          istr_contains(query, "bug")          ||
                          istr_contains(query, "build")        ||
                          istr_contains(query, "system")       ||
                          istr_contains(query, "design")       ||
                          istr_contains(query, "architecture");
    int personal_query  = istr_contains(query, "feel")         ||
                          istr_contains(query, "emotion")      ||
                          istr_contains(query, "remember")     ||
                          istr_contains(query, "personal")     ||
                          istr_contains(query, "story")        ||
                          istr_contains(query, "relationship");
    if (n->node_type) {
        int is_knowledge = (strcmp(n->node_type, "Belief")     == 0) ||
                           (strcmp(n->node_type, "DharmaSelf") == 0) ||
                           (strcmp(n->node_type, "Safety")     == 0);
        int is_personal  = (strcmp(n->node_type, "Memory")     == 0) ||
                           (strcmp(n->node_type, "Entity")     == 0);
        if (technical_query && is_knowledge) bias += 0.3;
        if (technical_query && is_personal)  bias -= 0.3;
        if (personal_query  && is_personal)  bias += 0.3;
        if (personal_query  && is_knowledge) bias -= 0.1;
    }
    /* Tier-based bonus: promote higher-confidence knowledge nodes. */
    if (n->tier) {
        if (strcmp(n->tier, "Canonical") == 0) bias += 0.2;
        if (strcmp(n->tier, "Lesson")    == 0) bias += 0.1;
    }
    if (bias < 0.3) bias = 0.3;
    if (bias > 2.0) bias = 2.0;
    return bias;
}

el_val_t engram_activate(el_val_t query, el_val_t depth) {
    EngramStore* g = engram_get();
    const char* q = EL_CSTR(query);
    int64_t max_depth = (int64_t)depth; if (max_depth <= 0) max_depth = 2;
    el_val_t out = el_list_empty();
    if (!q || g->node_count == 0) return out;

    int64_t now_ms = engram_now_ms();

    /* Per-node layer-1 tracking. */
    double*  best_bg    = calloc((size_t)g->node_count, sizeof(double));
    int64_t* best_hops  = calloc((size_t)g->node_count, sizeof(int64_t));
    int*     reached    = calloc((size_t)g->node_count, sizeof(int));
    if (!best_bg || !best_hops || !reached) {
        free(best_bg); free(best_hops); free(reached); return out;
    }

    /* ── LAYER 1: broad fan-out (background activation) ─────────────────
     * Find seeds, apply temporal decay + dampening, BFS with edge weights.
     * Inhibitory edges propagate activation normally at this layer — they
     * only gate working memory promotion in layer 2. */
    typedef struct { int64_t idx; double act; int64_t created_at; } SeedEntry;
    SeedEntry* seeds = malloc((size_t)g->node_count * sizeof(SeedEntry));
    int64_t seed_count = 0;
    if (!seeds) {
        free(best_bg); free(best_hops); free(reached); return out;
    }
    for (int64_t i = 0; i < g->node_count; i++) {
        EngramNode* n = &g->nodes[i];
        if (istr_contains(n->content, q) ||
            istr_contains(n->label,   q) ||
            istr_contains(n->tags,    q)) {
            double tdecay = engram_temporal_decay(n, now_ms);
            double dampen = engram_activation_dampen(n);
            double act    = n->salience * tdecay * dampen;
            seeds[seed_count].idx        = i;
            seeds[seed_count].act        = act;
            seeds[seed_count].created_at = n->created_at;
            seed_count++;
            best_bg[i]   = act;
            best_hops[i] = 0;
            reached[i]   = 1;
        }
    }
    /* Compute mean seed created_at for temporal proximity bonus. */
    int64_t seed_epoch = 0;
    if (seed_count > 0) {
        seed_epoch = seeds[0].created_at;
        for (int64_t s = 1; s < seed_count; s++)
            seed_epoch = (seed_epoch + seeds[s].created_at) / 2;
    }
    typedef struct { int64_t idx; int64_t hops; double act; } Frontier;
    Frontier* fr = malloc((size_t)(g->node_count * (max_depth + 1)) * sizeof(Frontier) + 16 * sizeof(Frontier));
    if (!fr) {
        free(best_bg); free(best_hops); free(reached); free(seeds); return out;
    }
    int64_t fhead = 0, ftail = 0;
    int64_t fcap = (int64_t)((size_t)(g->node_count * (max_depth + 1)) + 16);
    for (int64_t s = 0; s < seed_count; s++) {
        if (ftail >= fcap) break;
        fr[ftail].idx  = seeds[s].idx;
        fr[ftail].hops = 0;
        fr[ftail].act  = seeds[s].act;
        ftail++;
    }
    const double SPREAD_DECAY = 0.7;
    while (fhead < ftail) {
        Frontier f = fr[fhead++];
        if (f.hops >= max_depth) continue;
        const char* cur_id = g->nodes[f.idx].id;
        for (int64_t ei = 0; ei < g->edge_count; ei++) {
            EngramEdge* e = &g->edges[ei];
            const char* other = NULL;
            if (e->from_id && strcmp(e->from_id, cur_id) == 0) other = e->to_id;
            else if (e->to_id && strcmp(e->to_id, cur_id) == 0) other = e->from_id;
            else continue;
            int64_t oi = engram_find_node_index(other);
            if (oi < 0) continue;
            EngramNode* on = &g->nodes[oi];
            double tbonus  = engram_temporal_proximity_bonus(on->created_at, seed_epoch);
            double tdecay  = engram_temporal_decay(on, now_ms);
            double dampen  = engram_activation_dampen(on);
            double new_act = f.act * e->weight * SPREAD_DECAY * (1.0 + tbonus)
                           * tdecay * dampen;
            int64_t new_hops = f.hops + 1;
            if (!reached[oi] || new_act > best_bg[oi]) {
                best_bg[oi]   = new_act;
                best_hops[oi] = new_hops;
                reached[oi]   = 1;
                if (ftail < fcap) {
                    fr[ftail].idx  = oi;
                    fr[ftail].hops = new_hops;
                    fr[ftail].act  = new_act;
                    ftail++;
                }
            }
        }
    }
    /* Persist layer-1 background_activation to node store. */
    for (int64_t i = 0; i < g->node_count; i++) {
        g->nodes[i].background_activation = reached[i] ? best_bg[i] : 0.0;
    }

    /* ── PASS 2: executive filter → working memory promotion ──────────── */
    /* Step A: collect inhibitory suppressions from fired inhibitory edges.
     * Layered consciousness: inhibition is ONLY recorded against targets
     * whose layer is `suppressible == 1`. Nodes in non-suppressible layers
     * (Layer 0 / safety) ignore inhibitory edges entirely — their working
     * memory weight cannot be silenced by attentional suppression. */
    double* inhibition = calloc((size_t)g->node_count, sizeof(double));
    if (!inhibition) {
        free(best_bg); free(best_hops); free(reached); free(seeds); free(fr);
        return out;
    }
    for (int64_t ei = 0; ei < g->edge_count; ei++) {
        EngramEdge* e = &g->edges[ei];
        if (!e->inhibitory) continue;
        int64_t src = engram_find_node_index(e->from_id);
        int64_t tgt = engram_find_node_index(e->to_id);
        if (src < 0 || tgt < 0) continue;
        if (!reached[src] || best_bg[src] <= 0.0) continue;
        /* Skip if target layer is non-suppressible: Layer 0 / safety nodes
         * are immune to inhibitory edges from any source. The pass-3
         * override below also force-promotes them, but recording inhibition
         * against them at all would be wasted work and could confuse
         * downstream debugging output. */
        if (!engram_layer_is_suppressible(g->nodes[tgt].layer_id)) continue;
        /* Inhibition strength proportional to source background activation
         * and edge weight. Takes the maximum if multiple inhibitory edges
         * target the same node. */
        double inh = best_bg[src] * e->weight;
        if (inh > inhibition[tgt]) inhibition[tgt] = inh;
    }
    /* Step B: compute working_memory_weight per candidate node. */
    double* wm_weights = calloc((size_t)g->node_count, sizeof(double));
    if (!wm_weights) {
        free(best_bg); free(best_hops); free(reached); free(seeds);
        free(fr); free(inhibition); return out;
    }
    for (int64_t i = 0; i < g->node_count; i++) {
        if (!reached[i] || best_bg[i] <= 0.0) continue;
        EngramNode* n = &g->nodes[i];
        /* Per-type threshold: safety nodes break through more easily. */
        double type_threshold = engram_type_threshold(n->node_type, n->tier);
        /* Goal bias weights the node's relevance to current intent. */
        double bias = engram_goal_bias(n, q);
        /* Raw working memory score. */
        double raw_wm = best_bg[i] * bias * n->confidence;
        /* Apply inhibitory suppression. Full inhibition → scale by factor. */
        double inh = inhibition[i];
        if (inh > 1.0) inh = 1.0;
        double suppress = 1.0 - (1.0 - ENGRAM_INHIBITION_FACTOR) * inh;
        raw_wm *= suppress;
        /* Threshold gate: must exceed per-type threshold to enter working
         * memory. Type threshold replaces the old flat 0.2 filter. */
        if (raw_wm >= type_threshold) {
            wm_weights[i] = raw_wm > 1.0 ? 1.0 : raw_wm;
            if (n->suppression_count > 0) n->suppression_count = 0;
        } else {
            /* Node didn't make it through — increment suppression counter.
             * After N consecutive suppressions: force breakthrough. */
            n->suppression_count++;
            if (n->suppression_count >= ENGRAM_SUPPRESSION_BREAKTHROUGH) {
                wm_weights[i] = ENGRAM_BREAKTHROUGH_WEIGHT;
                n->suppression_count = 0;
            } else {
                wm_weights[i] = 0.0;
            }
        }
    }
    /* ── PASS 3: Layer 0 override (the sacred fire) ─────────────────────
     * Every node in a non-suppressible layer that received any background
     * activation is force-promoted to AT LEAST ENGRAM_LAYER0_OVERRIDE_WEIGHT.
     * This runs LAST and overrides whatever Pass 2 decided — Layer 0 cannot
     * be silenced by inhibitory edges, by goal-bias misalignment, by
     * confidence weighting, or by per-type threshold gates. If the seed
     * fan-out reached a structural-floor node, that node surfaces.
     *
     * Note: this also clears the suppression_count when an override fires,
     * since the node DID surface this turn — it just took the override path
     * rather than the standard threshold path. Without this, a Layer 0
     * node with persistent inhibitory pressure would accumulate
     * suppression_count forever and never reach the breakthrough state. */
    for (int64_t i = 0; i < g->node_count; i++) {
        if (!reached[i] || best_bg[i] <= 0.0) continue;
        EngramNode* n = &g->nodes[i];
        if (engram_layer_is_suppressible(n->layer_id)) continue;
        if (wm_weights[i] < ENGRAM_LAYER0_OVERRIDE_WEIGHT) {
            wm_weights[i] = ENGRAM_LAYER0_OVERRIDE_WEIGHT;
        }
        n->suppression_count = 0;
    }

    /* Persist working_memory_weight (post Pass 3) to node store. */
    for (int64_t i = 0; i < g->node_count; i++) {
        g->nodes[i].working_memory_weight = wm_weights[i];
    }

    /* ── Collect all background-activated nodes for the return value ────
     * Callers see both layers. Context compilation uses only promoted nodes
     * (working_memory_weight > 0). Sort: promoted first by wm_weight desc,
     * then background-only by background_activation desc. */
    typedef struct { int64_t idx; double bg; double wm; double epist; int64_t hops; } Result;
    Result* results = malloc((size_t)g->node_count * sizeof(Result));
    int64_t rcount = 0;
    if (!results) {
        free(best_bg); free(best_hops); free(reached); free(seeds);
        free(fr); free(inhibition); free(wm_weights); return out;
    }
    for (int64_t i = 0; i < g->node_count; i++) {
        if (!reached[i]) continue;
        double epist = best_bg[i] * g->nodes[i].confidence;
        /* Include if promoted to working memory OR if background activation
         * is meaningful enough to report (epist >= 0.1). */
        if (epist < 0.1 && wm_weights[i] <= 0.0) continue;
        results[rcount].idx   = i;
        results[rcount].bg    = best_bg[i];
        results[rcount].wm    = wm_weights[i];
        results[rcount].epist = epist;
        results[rcount].hops  = best_hops[i];
        rcount++;
    }
    /* Sort: promoted nodes first (by wm_weight desc), then background-only
     * by background_activation desc. */
    for (int64_t i = 1; i < rcount; i++) {
        Result key = results[i];
        int64_t j = i - 1;
        while (j >= 0 && (results[j].wm < key.wm ||
               (results[j].wm == key.wm && results[j].bg < key.bg))) {
            results[j + 1] = results[j];
            j--;
        }
        results[j + 1] = key;
    }
    for (int64_t i = 0; i < rcount; i++) {
        el_val_t entry = el_map_new(0);
        entry = el_map_set(entry, EL_STR(el_strdup("node")),
                           engram_node_to_map(&g->nodes[results[i].idx]));
        entry = el_map_set(entry, EL_STR(el_strdup("activation_strength")),
                           el_from_float(results[i].bg));
        entry = el_map_set(entry, EL_STR(el_strdup("working_memory_weight")),
                           el_from_float(results[i].wm));
        entry = el_map_set(entry, EL_STR(el_strdup("epistemic_confidence")),
                           el_from_float(results[i].epist));
        entry = el_map_set(entry, EL_STR(el_strdup("hops")),
                           (el_val_t)results[i].hops);
        entry = el_map_set(entry, EL_STR(el_strdup("promoted")),
                           (el_val_t)(results[i].wm > 0.0 ? 1 : 0));
        out = el_list_append(out, entry);
    }
    free(best_bg); free(best_hops); free(reached);
    free(seeds); free(fr); free(inhibition); free(wm_weights); free(results);
    return out;
}

/* ── Engram persistence (JSON snapshot) ─────────────────────────────────── */

static void engram_emit_node_json(JsonBuf* b, const EngramNode* n) {
    jb_putc(b, '{');
    jb_puts(b, "\"id\":");          jb_emit_escaped(b, n->id ? n->id : "");
    jb_puts(b, ",\"content\":");    jb_emit_escaped(b, n->content ? n->content : "");
    jb_puts(b, ",\"node_type\":");  jb_emit_escaped(b, n->node_type ? n->node_type : "");
    jb_puts(b, ",\"label\":");      jb_emit_escaped(b, n->label ? n->label : "");
    jb_puts(b, ",\"tier\":");       jb_emit_escaped(b, n->tier ? n->tier : "Working");
    jb_puts(b, ",\"tags\":");       jb_emit_escaped(b, n->tags ? n->tags : "");
    jb_puts(b, ",\"metadata\":");   jb_emit_escaped(b, n->metadata ? n->metadata : "{}");
    char tmp[80];
    snprintf(tmp, sizeof(tmp), ",\"salience\":%g",              n->salience);             jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"importance\":%g",            n->importance);            jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"confidence\":%g",            n->confidence);            jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"temporal_decay_rate\":%g",   n->temporal_decay_rate);   jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"activation_count\":%lld",   (long long)n->activation_count); jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"last_activated\":%lld",     (long long)n->last_activated);   jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"created_at\":%lld",         (long long)n->created_at);       jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"updated_at\":%lld",         (long long)n->updated_at);       jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"background_activation\":%g", n->background_activation); jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"working_memory_weight\":%g", n->working_memory_weight); jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"suppression_count\":%d",     n->suppression_count);     jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"layer_id\":%u",              n->layer_id);              jb_puts(b, tmp);
    jb_putc(b, '}');
}

static void engram_emit_edge_json(JsonBuf* b, const EngramEdge* e) {
    jb_putc(b, '{');
    jb_puts(b, "\"id\":");        jb_emit_escaped(b, e->id ? e->id : "");
    jb_puts(b, ",\"from_id\":");  jb_emit_escaped(b, e->from_id ? e->from_id : "");
    jb_puts(b, ",\"to_id\":");    jb_emit_escaped(b, e->to_id ? e->to_id : "");
    jb_puts(b, ",\"relation\":"); jb_emit_escaped(b, e->relation ? e->relation : "");
    jb_puts(b, ",\"metadata\":"); jb_emit_escaped(b, e->metadata ? e->metadata : "{}");
    char tmp[64];
    snprintf(tmp, sizeof(tmp), ",\"weight\":%g", e->weight);         jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"confidence\":%g", e->confidence); jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"created_at\":%lld", (long long)e->created_at); jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"updated_at\":%lld", (long long)e->updated_at); jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"last_fired\":%lld", (long long)e->last_fired); jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"inhibitory\":%d", e->inhibitory ? 1 : 0);     jb_puts(b, tmp);
    snprintf(tmp, sizeof(tmp), ",\"layer_id\":%u",   e->layer_id);               jb_puts(b, tmp);
    jb_putc(b, '}');
}

el_val_t engram_save(el_val_t path) {
    const char* p = EL_CSTR(path);
    if (!p || !*p) return 0;
    EngramStore* g = engram_get();
    JsonBuf b; jb_init(&b);
    jb_puts(&b, "{\"nodes\":[");
    for (int64_t i = 0; i < g->node_count; i++) {
        if (i > 0) jb_putc(&b, ',');
        engram_emit_node_json(&b, &g->nodes[i]);
    }
    jb_puts(&b, "],\"edges\":[");
    for (int64_t i = 0; i < g->edge_count; i++) {
        if (i > 0) jb_putc(&b, ',');
        engram_emit_edge_json(&b, &g->edges[i]);
    }
    /* Layered consciousness — emit the layer registry under "layers".
     * Older readers that don't know about this top-level key will simply
     * ignore it (forward compatible). Tombstoned (removed-injectable)
     * layers are skipped — they have no name and can't be re-created
     * meaningfully on load anyway. */
    jb_puts(&b, "],\"layers\":[");
    int first_layer = 1;
    for (size_t i = 0; i < g->layer_count; i++) {
        EngramLayer* L = &g->layers[i];
        if (!L->name) continue;
        if (!first_layer) jb_putc(&b, ',');
        first_layer = 0;
        jb_putc(&b, '{');
        char tmp[80];
        snprintf(tmp, sizeof(tmp), "\"layer_id\":%u", L->layer_id);
        jb_puts(&b, tmp);
        jb_puts(&b, ",\"name\":");
        jb_emit_escaped(&b, L->name);
        snprintf(tmp, sizeof(tmp), ",\"activation_priority\":%u", L->activation_priority);
        jb_puts(&b, tmp);
        snprintf(tmp, sizeof(tmp), ",\"suppressible\":%d", L->suppressible ? 1 : 0);
        jb_puts(&b, tmp);
        snprintf(tmp, sizeof(tmp), ",\"transparent\":%d", L->transparent ? 1 : 0);
        jb_puts(&b, tmp);
        snprintf(tmp, sizeof(tmp), ",\"injectable\":%d", L->injectable ? 1 : 0);
        jb_puts(&b, tmp);
        jb_putc(&b, '}');
    }
    jb_puts(&b, "]}");
    FILE* f = fopen(p, "wb");
    if (!f) { free(b.buf); return 0; }
    size_t w = fwrite(b.buf, 1, b.len, f);
    fclose(f);
    int ok = (w == b.len);
    free(b.buf);
    return ok ? 1 : 0;
}

/* Helper: extract a string field from a JSON object substring. */
static char* eg_get_str_field(const char* obj, const char* key) {
    const char* p = json_find_key(obj, key);
    if (!p) return el_strdup("");
    if (*p != '"') return el_strdup("");
    JsonParser jp = { .p = p, .end = p + strlen(p), .err = 0 };
    char* out = jp_parse_string_raw(&jp);
    if (jp.err) { free(out); return el_strdup(""); }
    return out;
}

static double eg_get_num_field(const char* obj, const char* key) {
    const char* p = json_find_key(obj, key);
    if (!p || *p == '"' || *p == '{' || *p == '[') return 0.0;
    return strtod(p, NULL);
}

static int64_t eg_get_int_field(const char* obj, const char* key) {
    const char* p = json_find_key(obj, key);
    if (!p || *p == '"' || *p == '{' || *p == '[') return 0;
    return strtoll(p, NULL, 10);
}

/* Iterate the top-level nodes/edges arrays in a saved snapshot. */
static const char* eg_skip_ws(const char* p) {
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    return p;
}

el_val_t engram_load(el_val_t path) {
    const char* p = EL_CSTR(path);
    if (!p || !*p) return 0;
    FILE* f = fopen(p, "rb");
    if (!f) return 0;
    fseek(f, 0, SEEK_END);
    long sz = ftell(f);
    rewind(f);
    if (sz <= 0) { fclose(f); return 0; }
    char* data = malloc((size_t)sz + 1);
    if (!data) { fclose(f); return 0; }
    size_t got = fread(data, 1, (size_t)sz, f);
    fclose(f);
    data[got] = '\0';

    /* Reset store */
    EngramStore* g = engram_get();
    for (int64_t i = 0; i < g->node_count; i++) {
        free(g->nodes[i].id); free(g->nodes[i].content); free(g->nodes[i].node_type);
        free(g->nodes[i].label); free(g->nodes[i].tier); free(g->nodes[i].tags);
        free(g->nodes[i].metadata);
    }
    g->node_count = 0;
    for (int64_t i = 0; i < g->edge_count; i++) {
        free(g->edges[i].id); free(g->edges[i].from_id); free(g->edges[i].to_id);
        free(g->edges[i].relation); free(g->edges[i].metadata);
    }
    g->edge_count = 0;

    /* Walk nodes array */
    const char* nodes_p = json_find_key(data, "nodes");
    if (nodes_p) {
        nodes_p = eg_skip_ws(nodes_p);
        if (*nodes_p == '[') {
            nodes_p++;
            nodes_p = eg_skip_ws(nodes_p);
            while (*nodes_p && *nodes_p != ']') {
                if (*nodes_p != '{') { nodes_p++; continue; }
                const char* end = json_skip_value(nodes_p);
                size_t n = (size_t)(end - nodes_p);
                char* obj = malloc(n + 1);
                memcpy(obj, nodes_p, n); obj[n] = '\0';
                engram_grow_nodes();
                EngramNode* nn = &g->nodes[g->node_count];
                memset(nn, 0, sizeof(*nn));
                nn->id        = eg_get_str_field(obj, "id");
                nn->content   = eg_get_str_field(obj, "content");
                nn->node_type = eg_get_str_field(obj, "node_type");
                nn->label     = eg_get_str_field(obj, "label");
                nn->tier      = eg_get_str_field(obj, "tier");
                nn->tags      = eg_get_str_field(obj, "tags");
                nn->metadata  = eg_get_str_field(obj, "metadata");
                if (!nn->metadata || !*nn->metadata) { free(nn->metadata); nn->metadata = el_strdup("{}"); }
                nn->salience           = eg_get_num_field(obj, "salience");
                nn->importance         = eg_get_num_field(obj, "importance");
                nn->confidence         = eg_get_num_field(obj, "confidence");
                nn->temporal_decay_rate = eg_get_num_field(obj, "temporal_decay_rate");
                /* temporal_decay_rate defaults to 0 (use global) if absent in snapshot */
                nn->activation_count      = eg_get_int_field(obj, "activation_count");
                nn->last_activated        = eg_get_int_field(obj, "last_activated");
                nn->created_at            = eg_get_int_field(obj, "created_at");
                nn->updated_at            = eg_get_int_field(obj, "updated_at");
                nn->background_activation = eg_get_num_field(obj, "background_activation");
                nn->working_memory_weight = eg_get_num_field(obj, "working_memory_weight");
                nn->suppression_count     = (int32_t)eg_get_int_field(obj, "suppression_count");
                /* layer_id defaults to ENGRAM_LAYER_DEFAULT (core-identity)
                 * for snapshots that predate the layered schema. We can't
                 * tell "explicit 0" from "missing field" using the helper
                 * directly, so probe for the key — if absent, fall back. */
                if (json_find_key(obj, "layer_id")) {
                    nn->layer_id = (uint32_t)eg_get_int_field(obj, "layer_id");
                } else {
                    nn->layer_id = ENGRAM_LAYER_DEFAULT;
                }
                g->node_count++;
                free(obj);
                nodes_p = end;
                nodes_p = eg_skip_ws(nodes_p);
                if (*nodes_p == ',') { nodes_p++; nodes_p = eg_skip_ws(nodes_p); }
            }
        }
    }
    /* Walk edges array */
    const char* edges_p = json_find_key(data, "edges");
    if (edges_p) {
        edges_p = eg_skip_ws(edges_p);
        if (*edges_p == '[') {
            edges_p++;
            edges_p = eg_skip_ws(edges_p);
            while (*edges_p && *edges_p != ']') {
                if (*edges_p != '{') { edges_p++; continue; }
                const char* end = json_skip_value(edges_p);
                size_t n = (size_t)(end - edges_p);
                char* obj = malloc(n + 1);
                memcpy(obj, edges_p, n); obj[n] = '\0';
                engram_grow_edges();
                EngramEdge* ee = &g->edges[g->edge_count];
                memset(ee, 0, sizeof(*ee));
                ee->id       = eg_get_str_field(obj, "id");
                ee->from_id  = eg_get_str_field(obj, "from_id");
                ee->to_id    = eg_get_str_field(obj, "to_id");
                ee->relation = eg_get_str_field(obj, "relation");
                ee->metadata = eg_get_str_field(obj, "metadata");
                if (!ee->metadata || !*ee->metadata) { free(ee->metadata); ee->metadata = el_strdup("{}"); }
                ee->weight     = eg_get_num_field(obj, "weight");
                ee->confidence = eg_get_num_field(obj, "confidence");
                ee->created_at = eg_get_int_field(obj, "created_at");
                ee->updated_at = eg_get_int_field(obj, "updated_at");
                ee->last_fired = eg_get_int_field(obj, "last_fired");
                ee->inhibitory = (int)eg_get_int_field(obj, "inhibitory");
                if (json_find_key(obj, "layer_id")) {
                    ee->layer_id = (uint32_t)eg_get_int_field(obj, "layer_id");
                } else {
                    ee->layer_id = ENGRAM_LAYER_DEFAULT;
                }
                g->edge_count++;
                free(obj);
                edges_p = end;
                edges_p = eg_skip_ws(edges_p);
                if (*edges_p == ',') { edges_p++; edges_p = eg_skip_ws(edges_p); }
            }
        }
    }
    /* Walk layers array (optional — older snapshots omit this).
     * If present we replace the canonical registry entirely; if absent we
     * keep whatever the engram_get() init established. */
    const char* layers_p = json_find_key(data, "layers");
    if (layers_p) {
        layers_p = eg_skip_ws(layers_p);
        if (*layers_p == '[') {
            /* Reset existing layer registry. Free strdup'd names; the
             * struct array itself can be reused. */
            for (size_t i = 0; i < g->layer_count; i++) {
                if (g->layers[i].name) free(g->layers[i].name);
                g->layers[i].name = NULL;
            }
            g->layer_count = 0;

            layers_p++;
            layers_p = eg_skip_ws(layers_p);
            while (*layers_p && *layers_p != ']') {
                if (*layers_p != '{') { layers_p++; continue; }
                const char* end = json_skip_value(layers_p);
                size_t n = (size_t)(end - layers_p);
                char* obj = malloc(n + 1);
                memcpy(obj, layers_p, n); obj[n] = '\0';
                if (g->layer_count >= g->layer_capacity) {
                    size_t nc = g->layer_capacity ? g->layer_capacity * 2 : 16;
                    EngramLayer* grown = realloc(g->layers, nc * sizeof(EngramLayer));
                    if (!grown) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
                    memset(grown + g->layer_capacity, 0,
                           (nc - g->layer_capacity) * sizeof(EngramLayer));
                    g->layers = grown;
                    g->layer_capacity = nc;
                }
                EngramLayer* L = &g->layers[g->layer_count];
                memset(L, 0, sizeof(*L));
                L->layer_id            = (uint32_t)eg_get_int_field(obj, "layer_id");
                L->activation_priority = (uint32_t)eg_get_int_field(obj, "activation_priority");
                L->suppressible        = (int)eg_get_int_field(obj, "suppressible") ? 1 : 0;
                L->transparent         = (int)eg_get_int_field(obj, "transparent")  ? 1 : 0;
                L->injectable          = (int)eg_get_int_field(obj, "injectable")   ? 1 : 0;
                char* nm = eg_get_str_field(obj, "name");
                if (nm && *nm) {
                    L->name = el_strdup_persist(nm);
                    free(nm);
                } else {
                    free(nm);
                    L->name = el_strdup_persist("");
                }
                g->layer_count++;
                free(obj);
                layers_p = end;
                layers_p = eg_skip_ws(layers_p);
                if (*layers_p == ',') { layers_p++; layers_p = eg_skip_ws(layers_p); }
            }
        }
    }
    free(data);
    return 1;
}

/* ── Engram JSON-string accessors ─────────────────────────────────────────
 * These return pre-serialized JSON strings so callers (especially HTTP
 * handlers) don't have to round-trip ElList/ElMap through json_stringify
 * — which can't reliably distinguish those structures from raw pointers
 * due to el_val_t's type erasure. The runtime knows the real C types and
 * can serialize directly. */

el_val_t engram_get_node_json(el_val_t id) {
    const char* sid = EL_CSTR(id);
    EngramNode* n = engram_find_node(sid);
    if (!n) return el_wrap_str(el_strdup("{}"));
    JsonBuf b; jb_init(&b);
    engram_emit_node_json(&b, n);
    return el_wrap_str(b.buf);
}

el_val_t engram_search_json(el_val_t query, el_val_t limit) {
    EngramStore* g = engram_get();
    const char* q = EL_CSTR(query);
    int64_t lim = (int64_t)limit;
    if (lim <= 0) lim = 100;
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '[');
    int first = 1;
    int64_t found = 0;
    if (q && *q) {
        for (int64_t i = 0; i < g->node_count && found < lim; i++) {
            EngramNode* n = &g->nodes[i];
            /* Filter transparent layers — same as engram_search. */
            if (engram_layer_is_transparent(n->layer_id)) continue;
            if (istr_contains(n->content, q) ||
                istr_contains(n->label,   q) ||
                istr_contains(n->tags,    q)) {
                if (!first) jb_putc(&b, ',');
                engram_emit_node_json(&b, n);
                first = 0;
                found++;
            }
        }
    }
    jb_putc(&b, ']');
    return el_wrap_str(b.buf);
}

el_val_t engram_scan_nodes_json(el_val_t limit, el_val_t offset) {
    EngramStore* g = engram_get();
    int64_t lim = (int64_t)limit; if (lim <= 0) lim = 100;
    int64_t off = (int64_t)offset; if (off < 0) off = 0;
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '[');
    if (g->node_count == 0) { jb_putc(&b, ']'); return el_wrap_str(b.buf); }
    int64_t* idx = malloc((size_t)g->node_count * sizeof(int64_t));
    if (!idx) { jb_putc(&b, ']'); return el_wrap_str(b.buf); }
    /* Skip transparent layers — introspection filter, same as engram_scan_nodes. */
    int64_t live = 0;
    for (int64_t i = 0; i < g->node_count; i++) {
        if (engram_layer_is_transparent(g->nodes[i].layer_id)) continue;
        idx[live++] = i;
    }
    engram_sort_indices_by_salience(idx, live, g->nodes);
    int64_t end = off + lim;
    if (end > live) end = live;
    int first = 1;
    for (int64_t i = off; i < end; i++) {
        if (!first) jb_putc(&b, ',');
        engram_emit_node_json(&b, &g->nodes[idx[i]]);
        first = 0;
    }
    free(idx);
    jb_putc(&b, ']');
    return el_wrap_str(b.buf);
}

/* engram_scan_nodes_by_type_json — filter by node_type before paginating.
 * Empty / NULL type_v falls back to the unfiltered scan (existing behaviour).
 * Result is JSON array, salience-sorted, transparent layers skipped. */
el_val_t engram_scan_nodes_by_type_json(el_val_t type_v, el_val_t limit, el_val_t offset) {
    const char* type_filter = EL_CSTR(type_v);
    if (!type_filter || !*type_filter) {
        return engram_scan_nodes_json(limit, offset);
    }
    EngramStore* g = engram_get();
    int64_t lim = (int64_t)limit; if (lim <= 0) lim = 100;
    int64_t off = (int64_t)offset; if (off < 0) off = 0;
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '[');
    if (g->node_count == 0) { jb_putc(&b, ']'); return el_wrap_str(b.buf); }
    int64_t* idx = malloc((size_t)g->node_count * sizeof(int64_t));
    if (!idx) { jb_putc(&b, ']'); return el_wrap_str(b.buf); }
    int64_t live = 0;
    for (int64_t i = 0; i < g->node_count; i++) {
        if (engram_layer_is_transparent(g->nodes[i].layer_id)) continue;
        const char* nt = g->nodes[i].node_type;
        if (!nt || strcmp(nt, type_filter) != 0) continue;
        idx[live++] = i;
    }
    engram_sort_indices_by_salience(idx, live, g->nodes);
    int64_t end = off + lim;
    if (end > live) end = live;
    int first = 1;
    for (int64_t i = off; i < end; i++) {
        if (!first) jb_putc(&b, ',');
        engram_emit_node_json(&b, &g->nodes[idx[i]]);
        first = 0;
    }
    free(idx);
    jb_putc(&b, ']');
    return el_wrap_str(b.buf);
}

el_val_t engram_neighbors_json(el_val_t node_id, el_val_t max_depth, el_val_t direction) {
    /* Re-implement here directly so we serialize without going through
     * the ElList path. Walks BFS to max_depth, emits {node, edge, hops}
     * triples. */
    EngramStore* g = engram_get();
    const char* sid = EL_CSTR(node_id);
    int64_t depth = (int64_t)max_depth; if (depth <= 0) depth = 1;
    const char* dir = EL_CSTR(direction); if (!dir) dir = "both";
    int allow_out = (strcmp(dir, "out") == 0) || (strcmp(dir, "both") == 0);
    int allow_in  = (strcmp(dir, "in")  == 0) || (strcmp(dir, "both") == 0);
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '[');
    if (!sid || !*sid) { jb_putc(&b, ']'); return el_wrap_str(b.buf); }

    /* Frontier of (node_id, hops). Cap to a sane size. */
    char** frontier = calloc(1024, sizeof(char*));
    int64_t* frontier_h = calloc(1024, sizeof(int64_t));
    int64_t fc = 0;
    char** visited = calloc(1024, sizeof(char*));
    int64_t vc = 0;
    if (!frontier || !frontier_h || !visited) {
        free(frontier); free(frontier_h); free(visited);
        jb_putc(&b, ']'); return el_wrap_str(b.buf);
    }
    /* Use plain strdup (not el_strdup) so arena doesn't track these pointers.
     * The BFS loop manually frees them below — arena would double-free them. */
    frontier[fc] = strdup(sid); frontier_h[fc] = 0; fc++;
    visited[vc++] = strdup(sid);

    int first = 1;
    while (fc > 0) {
        char* cur = frontier[0]; int64_t h = frontier_h[0];
        for (int64_t k = 1; k < fc; k++) { frontier[k-1] = frontier[k]; frontier_h[k-1] = frontier_h[k]; }
        fc--;
        if (h >= depth) { free(cur); continue; }
        for (int64_t i = 0; i < g->edge_count; i++) {
            EngramEdge* e = &g->edges[i];
            const char* peer = NULL;
            if (allow_out && e->from_id && strcmp(e->from_id, cur) == 0) peer = e->to_id;
            else if (allow_in && e->to_id && strcmp(e->to_id, cur) == 0) peer = e->from_id;
            if (!peer) continue;
            int seen = 0;
            for (int64_t v = 0; v < vc; v++) {
                if (strcmp(visited[v], peer) == 0) { seen = 1; break; }
            }
            if (seen) continue;
            EngramNode* n = engram_find_node(peer);
            if (!n) continue;
            if (!first) jb_putc(&b, ',');
            jb_puts(&b, "{\"node\":");
            engram_emit_node_json(&b, n);
            jb_puts(&b, ",\"edge\":");
            engram_emit_edge_json(&b, e);
            char tmp[64]; snprintf(tmp, sizeof(tmp), ",\"hops\":%lld}", (long long)(h + 1));
            jb_puts(&b, tmp);
            first = 0;
            if (vc < 1024) visited[vc++] = strdup(peer);
            if (fc < 1024 && h + 1 < depth) { frontier[fc] = strdup(peer); frontier_h[fc] = h + 1; fc++; }
        }
        free(cur);
    }
    for (int64_t i = 0; i < fc; i++) free(frontier[i]);
    for (int64_t i = 0; i < vc; i++) free(visited[i]);
    free(frontier); free(frontier_h); free(visited);
    jb_putc(&b, ']');
    return el_wrap_str(b.buf);
}

el_val_t engram_activate_json(el_val_t query, el_val_t depth) {
    /* Run two-layer engram_activate and serialize the result list to JSON.
     * Each entry includes both activation_strength (layer 1 background) and
     * working_memory_weight (layer 2 executive filter), plus promoted flag.
     * Callers performing context compilation should filter to promoted=1. */
    el_val_t lst = engram_activate(query, depth);
    ElList* arr = (ElList*)(uintptr_t)lst;
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '[');
    if (arr) {
        for (int64_t i = 0; i < arr->length; i++) {
            if (!arr->elems[i]) continue;
            el_val_t node_map   = el_map_get(arr->elems[i], EL_STR("node"));
            el_val_t strength_v = el_map_get(arr->elems[i], EL_STR("activation_strength"));
            el_val_t wm_v       = el_map_get(arr->elems[i], EL_STR("working_memory_weight"));
            el_val_t epist_v    = el_map_get(arr->elems[i], EL_STR("epistemic_confidence"));
            el_val_t hops_v     = el_map_get(arr->elems[i], EL_STR("hops"));
            el_val_t promoted_v = el_map_get(arr->elems[i], EL_STR("promoted"));
            /* Look up underlying EngramNode by id to emit canonical JSON. */
            el_val_t id_v    = el_map_get(node_map, EL_STR("id"));
            const char* id_s = EL_CSTR(id_v);
            EngramNode* n    = id_s ? engram_find_node(id_s) : NULL;
            if (i > 0) jb_putc(&b, ',');
            jb_puts(&b, "{\"node\":");
            if (n) {
                engram_emit_node_json(&b, n);
            } else {
                jb_puts(&b, "{}");
            }
            char tmp[80];
            snprintf(tmp, sizeof(tmp), ",\"activation_strength\":%g",   el_to_float(strength_v)); jb_puts(&b, tmp);
            snprintf(tmp, sizeof(tmp), ",\"working_memory_weight\":%g", el_to_float(wm_v));        jb_puts(&b, tmp);
            snprintf(tmp, sizeof(tmp), ",\"epistemic_confidence\":%g",  el_to_float(epist_v));     jb_puts(&b, tmp);
            snprintf(tmp, sizeof(tmp), ",\"hops\":%lld",  (long long)(int64_t)hops_v);             jb_puts(&b, tmp);
            snprintf(tmp, sizeof(tmp), ",\"promoted\":%d}",  (int)(int64_t)promoted_v);            jb_puts(&b, tmp);
        }
    }
    jb_putc(&b, ']');
    return el_wrap_str(b.buf);
}

el_val_t engram_stats_json(void) {
    EngramStore* g = engram_get();
    char buf[128];
    snprintf(buf, sizeof(buf),
             "{\"node_count\":%lld,\"edge_count\":%lld,\"layer_count\":%zu}",
             (long long)g->node_count, (long long)g->edge_count, g->layer_count);
    return el_wrap_str(el_strdup(buf));
}

/* engram_list_layers_json — serialized counterpart of engram_list_layers.
 * Returns a JSON array, sorted by activation_priority ascending. */
el_val_t engram_list_layers_json(void) {
    EngramStore* g = engram_get();
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '[');
    /* Build a sorted index over live layers. */
    size_t* idx = malloc((g->layer_count + 1) * sizeof(size_t));
    if (!idx) { jb_putc(&b, ']'); return el_wrap_str(b.buf); }
    size_t live = 0;
    for (size_t i = 0; i < g->layer_count; i++) {
        if (g->layers[i].name) idx[live++] = i;
    }
    for (size_t i = 1; i < live; i++) {
        size_t key = idx[i];
        uint32_t kp = g->layers[key].activation_priority;
        size_t j = i;
        while (j > 0 && g->layers[idx[j - 1]].activation_priority > kp) {
            idx[j] = idx[j - 1];
            j--;
        }
        idx[j] = key;
    }
    int first = 1;
    for (size_t i = 0; i < live; i++) {
        EngramLayer* L = &g->layers[idx[i]];
        if (!first) jb_putc(&b, ',');
        first = 0;
        jb_putc(&b, '{');
        char tmp[80];
        snprintf(tmp, sizeof(tmp), "\"layer_id\":%u", L->layer_id);  jb_puts(&b, tmp);
        jb_puts(&b, ",\"name\":");
        jb_emit_escaped(&b, L->name ? L->name : "");
        snprintf(tmp, sizeof(tmp), ",\"activation_priority\":%u", L->activation_priority);
        jb_puts(&b, tmp);
        snprintf(tmp, sizeof(tmp), ",\"suppressible\":%d", L->suppressible ? 1 : 0);
        jb_puts(&b, tmp);
        snprintf(tmp, sizeof(tmp), ",\"transparent\":%d", L->transparent ? 1 : 0);
        jb_puts(&b, tmp);
        snprintf(tmp, sizeof(tmp), ",\"injectable\":%d", L->injectable ? 1 : 0);
        jb_puts(&b, tmp);
        jb_putc(&b, '}');
    }
    free(idx);
    jb_putc(&b, ']');
    return el_wrap_str(b.buf);
}

/* engram_compile_layered_json — produce a prompt-ready context block split
 * by layer.
 *
 * Runs the three-pass activation, then partitions promoted nodes by layer
 * suppressibility:
 *   - Non-suppressible (Layer 0 / structural-floor) layers go FIRST under
 *     the heading "[LAYER 0 — STRUCTURAL]". These are the sacred-fire
 *     nodes that surfaced via the pass-3 override.
 *   - All other promoted layers go SECOND under "[ENGRAM CONTEXT]".
 *
 * Output is a single JSON-string el_val_t: a UTF-8 text block ready to be
 * concatenated into a system prompt. Returns "" if no nodes promoted.
 *
 * Transparent layers (Layer 0) are emitted into the prompt — they shape
 * the model's output — but engram_search and friends still hide them from
 * introspection-style queries. The split heading lets the LLM weight them
 * appropriately without revealing their internal label.
 *
 * Each emitted line for a node is its raw JSON (matching engram_emit_node_json)
 * so downstream JSON parsers can still walk individual records inside the
 * formatted block. The block is plain text, not a JSON document — callers
 * concatenating it into a prompt should treat it as opaque markdown. */
el_val_t engram_compile_layered_json(el_val_t intent, el_val_t depth) {
    EngramStore* g = engram_get();
    /* Run the three-pass activator. We need the persisted node fields, so
     * call engram_activate (it writes background_activation and
     * working_memory_weight back into the store). */
    (void)engram_activate(intent, depth);

    /* Walk the store and partition by suppressibility. */
    JsonBuf b; jb_init(&b);
    int wrote_layer0 = 0;
    int wrote_normal = 0;

    /* Sort indices by working_memory_weight descending so the most
     * confidently promoted nodes appear first within each section. */
    int64_t* idx = malloc((size_t)(g->node_count + 1) * sizeof(int64_t));
    if (!idx) return el_wrap_str(el_strdup(""));
    int64_t mc = 0;
    for (int64_t i = 0; i < g->node_count; i++) {
        if (g->nodes[i].working_memory_weight > 0.0) idx[mc++] = i;
    }
    for (int64_t i = 1; i < mc; i++) {
        int64_t key = idx[i];
        double  kw  = g->nodes[key].working_memory_weight;
        int64_t j = i;
        while (j > 0 && g->nodes[idx[j - 1]].working_memory_weight < kw) {
            idx[j] = idx[j - 1];
            j--;
        }
        idx[j] = key;
    }

    /* Section 1: structural floor (non-suppressible layers). */
    for (int64_t i = 0; i < mc; i++) {
        EngramNode* n = &g->nodes[idx[i]];
        if (engram_layer_is_suppressible(n->layer_id)) continue;
        if (!wrote_layer0) {
            jb_puts(&b, "[LAYER 0 — STRUCTURAL]\n");
            wrote_layer0 = 1;
        }
        engram_emit_node_json(&b, n);
        jb_putc(&b, '\n');
    }

    /* Section 2: standard engram context (suppressible layers). */
    for (int64_t i = 0; i < mc; i++) {
        EngramNode* n = &g->nodes[idx[i]];
        if (!engram_layer_is_suppressible(n->layer_id)) continue;
        if (!wrote_normal) {
            if (wrote_layer0) jb_putc(&b, '\n');
            jb_puts(&b, "[ENGRAM CONTEXT]\n");
            wrote_normal = 1;
        }
        engram_emit_node_json(&b, n);
        jb_putc(&b, '\n');
    }

    free(idx);
    if (b.len == 0) {
        free(b.buf);
        return el_wrap_str(el_strdup(""));
    }
    return el_wrap_str(b.buf);
}

/* engram_query_range — temporal range query.
 * Returns a JSON array of nodes whose created_at OR last_activated falls
 * within [start_ms, end_ms], sorted by created_at ascending.
 * Enables "what was I working on last Tuesday?" style queries by passing
 * unix-millisecond timestamps for the start and end of the target interval.
 * Both endpoints are inclusive. Pass 0 for start_ms to mean "beginning of
 * time"; pass 0 for end_ms to mean "now". */
el_val_t engram_query_range(el_val_t start_ms_v, el_val_t end_ms_v) {
    EngramStore* g = engram_get();
    int64_t start_ms = (int64_t)start_ms_v;
    int64_t end_ms   = (int64_t)end_ms_v;
    if (end_ms <= 0) end_ms = engram_now_ms();

    /* Collect matching indices. */
    int64_t* idx = malloc((size_t)g->node_count * sizeof(int64_t));
    if (!idx) return el_wrap_str(el_strdup("[]"));
    int64_t mc = 0;
    for (int64_t i = 0; i < g->node_count; i++) {
        EngramNode* n = &g->nodes[i];
        int in_created  = (n->created_at    >= start_ms && n->created_at    <= end_ms);
        int in_activated = (n->last_activated >= start_ms && n->last_activated <= end_ms);
        if (in_created || in_activated) idx[mc++] = i;
    }
    /* Sort by created_at ascending (insertion sort — N is small in practice). */
    for (int64_t i = 1; i < mc; i++) {
        int64_t key = idx[i];
        int64_t kts = g->nodes[key].created_at;
        int64_t j = i - 1;
        while (j >= 0 && g->nodes[idx[j]].created_at > kts) {
            idx[j + 1] = idx[j];
            j--;
        }
        idx[j + 1] = key;
    }
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '[');
    for (int64_t i = 0; i < mc; i++) {
        if (i > 0) jb_putc(&b, ',');
        engram_emit_node_json(&b, &g->nodes[idx[i]]);
    }
    jb_putc(&b, ']');
    free(idx);
    return el_wrap_str(b.buf);
}

#ifdef HAVE_CURL
/* ── DHARMA network ─────────────────────────────────────────────────────────
 * Real implementation. Peers are addressed by `dharma_id` — either bare
 * (e.g. "ntn-genesis", transport defaults to http://localhost:7770) or
 * "<id>@<url>" where <url> is the peer's Engram-exposed daemon.
 *
 * Channels are logical handles cached per-cgi: `dharma_connect` is
 * idempotent and returns "ch:<cgi_id>". The channel registry below tracks
 * every cgi_id we've connected to and its resolved transport URL.
 *
 * Relationship weights live in the local Engram graph: edges of type
 * "dharma-relation" between a synthetic local node ("dharma:self") and
 * synthetic peer nodes ("dharma:peer:<cgi_id>"). Hebbian increments
 * accumulate in EngramEdge.weight, clamped to [0.0, 1.0].
 *
 * Events arrive over HTTP via the application's request handler, which is
 * expected to call el_runtime_dharma_event_arrive() when it sees a
 * /dharma/event POST. dharma_field() blocks on a per-event-type queue.
 */

#define DHARMA_DEFAULT_URL "http://localhost:7770"

/* Channel registry — one entry per known peer.                             */
typedef struct DharmaChannel {
    char* cgi_id;       /* full dharma_id including any @<url> suffix */
    char* base_id;      /* registry-id portion (before @) for relationship lookup */
    char* url;          /* resolved transport URL */
    char* channel_id;   /* "ch:<cgi_id>" */
} DharmaChannel;

static DharmaChannel* _dharma_channels = NULL;
static size_t         _dharma_channel_count = 0;
static size_t         _dharma_channel_cap   = 0;
static pthread_mutex_t _dharma_channel_mu   = PTHREAD_MUTEX_INITIALIZER;

/* Event queue — per-type linked list. dharma_field blocks on _dharma_event_cv. */
typedef struct DharmaEvent {
    char* event_type;
    char* payload;
    char* source;
    int64_t timestamp;
    struct DharmaEvent* next;
} DharmaEvent;

static DharmaEvent*   _dharma_event_head = NULL;
static DharmaEvent*   _dharma_event_tail = NULL;
static pthread_mutex_t _dharma_event_mu  = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t  _dharma_event_cv  = PTHREAD_COND_INITIALIZER;

/* Split "<id>@<url>" → (base_id, url). If no "@", base_id = full, url = default.
 * Returned strings are heap-allocated; caller must free.                    */
static void dharma_parse_id(const char* full, char** out_base, char** out_url) {
    if (!full) full = "";
    const char* at = strchr(full, '@');
    if (at) {
        size_t bn = (size_t)(at - full);
        char* b = malloc(bn + 1);
        memcpy(b, full, bn); b[bn] = '\0';
        *out_base = b;
        *out_url  = el_strdup(at + 1);
        if (!**out_url) { free(*out_url); *out_url = el_strdup(DHARMA_DEFAULT_URL); }
    } else {
        *out_base = el_strdup(full);
        *out_url  = el_strdup(DHARMA_DEFAULT_URL);
    }
}

/* Find existing channel by full cgi_id. Caller must hold _dharma_channel_mu. */
static DharmaChannel* dharma_find_channel_locked(const char* cgi_id) {
    if (!cgi_id) return NULL;
    for (size_t i = 0; i < _dharma_channel_count; i++) {
        if (_dharma_channels[i].cgi_id &&
            strcmp(_dharma_channels[i].cgi_id, cgi_id) == 0) {
            return &_dharma_channels[i];
        }
    }
    return NULL;
}

/* Add a new channel entry. Caller must hold _dharma_channel_mu.            */
static DharmaChannel* dharma_add_channel_locked(const char* cgi_id) {
    if (_dharma_channel_count >= _dharma_channel_cap) {
        size_t nc = _dharma_channel_cap ? _dharma_channel_cap * 2 : 8;
        _dharma_channels = realloc(_dharma_channels, nc * sizeof(DharmaChannel));
        if (!_dharma_channels) { fputs("el_runtime: out of memory\n", stderr); exit(1); }
        memset(_dharma_channels + _dharma_channel_cap, 0,
               (nc - _dharma_channel_cap) * sizeof(DharmaChannel));
        _dharma_channel_cap = nc;
    }
    DharmaChannel* ch = &_dharma_channels[_dharma_channel_count++];
    char* base = NULL; char* url = NULL;
    dharma_parse_id(cgi_id, &base, &url);
    ch->cgi_id  = el_strdup(cgi_id ? cgi_id : "");
    ch->base_id = base;
    ch->url     = url;
    size_t cn = strlen(ch->cgi_id) + 4;
    ch->channel_id = malloc(cn);
    snprintf(ch->channel_id, cn, "ch:%s", ch->cgi_id);
    return ch;
}

el_val_t dharma_connect(el_val_t cgi_id) {
    const char* id = EL_CSTR(cgi_id);
    if (!id || !*id) return el_wrap_str(el_strdup(""));
    pthread_mutex_lock(&_dharma_channel_mu);
    DharmaChannel* ch = dharma_find_channel_locked(id);
    if (!ch) ch = dharma_add_channel_locked(id);
    char* out = el_strdup(ch->channel_id);
    pthread_mutex_unlock(&_dharma_channel_mu);
    return el_wrap_str(out);
}

/* Build an error JSON body — same shape http_error_json uses. */
static el_val_t dharma_error_json(const char* msg) {
    return http_error_json(msg);
}

el_val_t dharma_send(el_val_t channel, el_val_t content) {
    const char* ch_id = EL_CSTR(channel);
    const char* msg   = EL_CSTR(content);
    if (!ch_id || strncmp(ch_id, "ch:", 3) != 0) {
        return dharma_error_json("invalid channel");
    }
    const char* peer_id = ch_id + 3;
    /* Look up channel; if unknown (caller fabricated), auto-register. */
    pthread_mutex_lock(&_dharma_channel_mu);
    DharmaChannel* ch = dharma_find_channel_locked(peer_id);
    if (!ch) ch = dharma_add_channel_locked(peer_id);
    char* url  = el_strdup(ch->url);
    pthread_mutex_unlock(&_dharma_channel_mu);
    /* Build /dharma/recv body. */
    const char* from = _el_cgi_dharma_id ? _el_cgi_dharma_id : "(unknown)";
    char* esc_ch   = json_escape_alloc(ch_id);
    char* esc_from = json_escape_alloc(from);
    char* esc_msg  = json_escape_alloc(msg ? msg : "");
    JsonBuf b; jb_init(&b);
    jb_puts(&b, "{\"channel\":\"");  jb_puts(&b, esc_ch);
    jb_puts(&b, "\",\"from\":\"");   jb_puts(&b, esc_from);
    jb_puts(&b, "\",\"content\":\""); jb_puts(&b, esc_msg);
    jb_puts(&b, "\"}");
    free(esc_ch); free(esc_from); free(esc_msg);
    size_t ul = strlen(url) + 16;
    char* full_url = malloc(ul);
    snprintf(full_url, ul, "%s/dharma/recv", url);
    struct curl_slist* h = NULL;
    h = curl_slist_append(h, "Content-Type: application/json");
    el_val_t resp = http_do("POST", full_url, b.buf, h);
    curl_slist_free_all(h);
    free(b.buf); free(full_url); free(url);
    return resp;
}

el_val_t dharma_activate(el_val_t query) {
    const char* q = EL_CSTR(query);
    if (!q) q = "";
    el_val_t out = el_list_empty();
    char* esc_q = json_escape_alloc(q);
    JsonBuf body; jb_init(&body);
    jb_puts(&body, "{\"query\":\""); jb_puts(&body, esc_q); jb_puts(&body, "\"}");
    free(esc_q);

    /* Snapshot the channel list under lock so we can iterate without
     * holding the mutex during network I/O.                                */
    pthread_mutex_lock(&_dharma_channel_mu);
    size_t n = _dharma_channel_count;
    char** urls   = calloc(n ? n : 1, sizeof(char*));
    char** ids    = calloc(n ? n : 1, sizeof(char*));
    char** bases  = calloc(n ? n : 1, sizeof(char*));
    for (size_t i = 0; i < n; i++) {
        urls[i]  = el_strdup(_dharma_channels[i].url);
        ids[i]   = el_strdup(_dharma_channels[i].cgi_id);
        bases[i] = el_strdup(_dharma_channels[i].base_id);
    }
    pthread_mutex_unlock(&_dharma_channel_mu);

    for (size_t i = 0; i < n; i++) {
        size_t ul = strlen(urls[i]) + 32;
        char* full_url = malloc(ul);
        snprintf(full_url, ul, "%s/api/activate", urls[i]);
        struct curl_slist* h = NULL;
        h = curl_slist_append(h, "Content-Type: application/json");
        el_val_t resp = http_do("POST", full_url, body.buf, h);
        curl_slist_free_all(h);
        free(full_url);
        const char* rs = EL_CSTR(resp);
        if (!rs || !*rs) continue;
        if (rs[0] == '{' && strstr(rs, "\"error\"")) continue;

        /* Look up relationship weight (attenuation). */
        double rel_weight = 1.0;
        {
            const char* self_id = "dharma:self";
            char peer_node[512];
            snprintf(peer_node, sizeof(peer_node), "dharma:peer:%s", bases[i]);
            EngramStore* g = engram_get();
            for (int64_t k = 0; k < g->edge_count; k++) {
                EngramEdge* e = &g->edges[k];
                if (e->from_id && e->to_id &&
                    strcmp(e->from_id, self_id) == 0 &&
                    strcmp(e->to_id, peer_node) == 0 &&
                    e->relation && strcmp(e->relation, "dharma-relation") == 0) {
                    rel_weight = e->weight;
                    break;
                }
            }
        }

        /* Iterate the response array. Expect either a top-level array
         * or an object whose "results" field is an array.                 */
        const char* arr = rs;
        while (*arr == ' ' || *arr == '\t' || *arr == '\n' || *arr == '\r') arr++;
        char* arr_owned = NULL;
        if (*arr == '{') {
            el_val_t r = json_get_raw(EL_STR(rs), EL_STR("results"));
            const char* rr = EL_CSTR(r);
            if (rr && *rr == '[') {
                arr_owned = el_strdup(rr);
                arr = arr_owned;
            } else {
                continue;
            }
        }
        if (*arr != '[') { free(arr_owned); continue; }
        const char* p = arr + 1;
        while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
        while (*p && *p != ']') {
            const char* end = json_skip_value(p);
            size_t en = (size_t)(end - p);
            char* obj = el_strbuf(en);
            memcpy(obj, p, en); obj[en] = '\0';

            /* Pull activation_strength if present, else 1.0. */
            el_val_t act_v = json_get_float(EL_STR(obj), EL_STR("activation_strength"));
            double act = el_to_float(act_v);
            if (!(act > 0.0 && act <= 100.0)) act = 1.0;
            double final_act = act * rel_weight;

            el_val_t entry = el_map_new(0);
            /* node = the inner JSON if present, else the entire obj. */
            el_val_t node_raw = json_get_raw(EL_STR(obj), EL_STR("node"));
            const char* nr = EL_CSTR(node_raw);
            entry = el_map_set(entry, EL_STR(el_strdup("node")),
                               (nr && *nr) ? node_raw : EL_STR(el_strdup(obj)));
            entry = el_map_set(entry, EL_STR(el_strdup("source_cgi")),
                               EL_STR(el_strdup(ids[i])));
            entry = el_map_set(entry, EL_STR(el_strdup("activation_strength")),
                               el_from_float(final_act));
            out = el_list_append(out, entry);
            free(obj);
            p = end;
            while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r' || *p == ',') p++;
        }
        free(arr_owned);
    }
    for (size_t i = 0; i < n; i++) { free(urls[i]); free(ids[i]); free(bases[i]); }
    free(urls); free(ids); free(bases);
    free(body.buf);
    return out;
}

void dharma_emit(el_val_t event_type, el_val_t payload) {
    const char* et  = EL_CSTR(event_type);
    const char* pay = EL_CSTR(payload);
    if (!et)  et  = "";
    if (!pay) pay = "";
    const char* src = _el_cgi_dharma_id ? _el_cgi_dharma_id : "(unknown)";
    int64_t ts = engram_now_ms();

    char* esc_et  = json_escape_alloc(et);
    char* esc_pay = json_escape_alloc(pay);
    char* esc_src = json_escape_alloc(src);
    JsonBuf b; jb_init(&b);
    jb_puts(&b, "{\"type\":\"");      jb_puts(&b, esc_et);
    jb_puts(&b, "\",\"payload\":\""); jb_puts(&b, esc_pay);
    jb_puts(&b, "\",\"source\":\"");  jb_puts(&b, esc_src);
    jb_puts(&b, "\",\"timestamp\":"); jb_emit_int(&b, ts);
    jb_putc(&b, '}');
    free(esc_et); free(esc_pay); free(esc_src);

    /* Snapshot URLs to avoid holding the channel mutex during I/O. */
    pthread_mutex_lock(&_dharma_channel_mu);
    size_t n = _dharma_channel_count;
    char** urls = calloc(n ? n : 1, sizeof(char*));
    for (size_t i = 0; i < n; i++) urls[i] = el_strdup(_dharma_channels[i].url);
    pthread_mutex_unlock(&_dharma_channel_mu);

    for (size_t i = 0; i < n; i++) {
        size_t ul = strlen(urls[i]) + 32;
        char* full_url = malloc(ul);
        snprintf(full_url, ul, "%s/dharma/event", urls[i]);
        struct curl_slist* h = NULL;
        h = curl_slist_append(h, "Content-Type: application/json");
        el_val_t r = http_do("POST", full_url, b.buf, h);
        (void)r; /* fire-and-forget — emit is not synchronous */
        curl_slist_free_all(h);
        free(full_url);
    }
    for (size_t i = 0; i < n; i++) free(urls[i]);
    free(urls);
    free(b.buf);
}

void el_runtime_dharma_event_arrive(const char* event_type, const char* payload,
                                    const char* source) {
    DharmaEvent* ev = calloc(1, sizeof(DharmaEvent));
    if (!ev) return;
    ev->event_type = el_strdup(event_type ? event_type : "");
    ev->payload    = el_strdup(payload    ? payload    : "");
    ev->source     = el_strdup(source     ? source     : "");
    ev->timestamp  = engram_now_ms();
    ev->next       = NULL;
    pthread_mutex_lock(&_dharma_event_mu);
    if (_dharma_event_tail) _dharma_event_tail->next = ev;
    else                    _dharma_event_head = ev;
    _dharma_event_tail = ev;
    pthread_cond_broadcast(&_dharma_event_cv);
    pthread_mutex_unlock(&_dharma_event_mu);
}

el_val_t dharma_field(el_val_t event_type) {
    const char* et = EL_CSTR(event_type);
    if (!et) et = "";

    /* Compute deadline: now + 30 seconds. */
    struct timespec deadline;
    clock_gettime(CLOCK_REALTIME, &deadline);
    deadline.tv_sec += 30;

    DharmaEvent* found = NULL;
    pthread_mutex_lock(&_dharma_event_mu);
    while (1) {
        /* Scan queue for matching type; pop and return first match. */
        DharmaEvent* prev = NULL;
        DharmaEvent* cur  = _dharma_event_head;
        while (cur) {
            if (cur->event_type && strcmp(cur->event_type, et) == 0) {
                if (prev) prev->next = cur->next;
                else      _dharma_event_head = cur->next;
                if (_dharma_event_tail == cur) _dharma_event_tail = prev;
                cur->next = NULL;
                found = cur;
                break;
            }
            prev = cur; cur = cur->next;
        }
        if (found) break;
        int rc = pthread_cond_timedwait(&_dharma_event_cv, &_dharma_event_mu, &deadline);
        if (rc == ETIMEDOUT) break;
    }
    pthread_mutex_unlock(&_dharma_event_mu);

    if (!found) return el_map_new(0);
    el_val_t m = el_map_new(0);
    m = el_map_set(m, EL_STR(el_strdup("type")),
                   EL_STR(el_strdup(found->event_type ? found->event_type : "")));
    m = el_map_set(m, EL_STR(el_strdup("payload")),
                   EL_STR(el_strdup(found->payload ? found->payload : "")));
    m = el_map_set(m, EL_STR(el_strdup("source_cgi")),
                   EL_STR(el_strdup(found->source ? found->source : "")));
    m = el_map_set(m, EL_STR(el_strdup("timestamp")), (el_val_t)found->timestamp);
    free(found->event_type); free(found->payload); free(found->source); free(found);
    return m;
}

/* Locate (or create) the local "dharma:self" node and the synthetic peer
 * node "dharma:peer:<base_id>". Returns the index of the dharma-relation
 * edge, or -1 if not found. If `create` is non-zero, ensure the nodes
 * and edge exist (creating them as needed) and return the edge index.   */
static int64_t dharma_find_or_create_relation_edge(const char* peer_base, int create) {
    if (!peer_base || !*peer_base) return -1;
    EngramStore* g = engram_get();
    const char* self_id = "dharma:self";
    char peer_node[512];
    snprintf(peer_node, sizeof(peer_node), "dharma:peer:%s", peer_base);

    /* Look for the edge first. */
    for (int64_t i = 0; i < g->edge_count; i++) {
        EngramEdge* e = &g->edges[i];
        if (e->from_id && e->to_id &&
            strcmp(e->from_id, self_id) == 0 &&
            strcmp(e->to_id, peer_node) == 0 &&
            e->relation && strcmp(e->relation, "dharma-relation") == 0) {
            return i;
        }
    }
    if (!create) return -1;

    /* Ensure self node exists. We use a fixed id (not engram_new_id) so
     * subsequent calls reuse the same one.                              */
    if (!engram_find_node(self_id)) {
        engram_grow_nodes();
        EngramNode* n = &g->nodes[g->node_count];
        memset(n, 0, sizeof(*n));
        n->id        = el_strdup(self_id);
        n->content   = el_strdup(_el_cgi_dharma_id ? _el_cgi_dharma_id : "(self)");
        n->node_type = el_strdup("DharmaSelf");
        n->label     = el_strdup("dharma:self");
        n->tier      = el_strdup("Working");
        n->tags      = el_strdup("dharma");
        n->metadata  = el_strdup("{}");
        n->salience  = 1.0; n->importance = 1.0; n->confidence = 1.0;
        int64_t now  = engram_now_ms();
        n->created_at = now; n->updated_at = now; n->last_activated = now;
        n->layer_id  = ENGRAM_LAYER_DEFAULT;
        g->node_count++;
    }
    if (!engram_find_node(peer_node)) {
        engram_grow_nodes();
        EngramNode* n = &g->nodes[g->node_count];
        memset(n, 0, sizeof(*n));
        n->id        = el_strdup(peer_node);
        n->content   = el_strdup(peer_base);
        n->node_type = el_strdup("DharmaPeer");
        n->label     = el_strdup(peer_node);
        n->tier      = el_strdup("Working");
        n->tags      = el_strdup("dharma");
        n->metadata  = el_strdup("{}");
        n->salience  = 0.5; n->importance = 0.5; n->confidence = 1.0;
        int64_t now  = engram_now_ms();
        n->created_at = now; n->updated_at = now; n->last_activated = now;
        n->layer_id  = ENGRAM_LAYER_DEFAULT;
        g->node_count++;
    }
    /* Create the edge with weight 0.0 — caller will increment. */
    engram_grow_edges();
    EngramEdge* e = &g->edges[g->edge_count];
    memset(e, 0, sizeof(*e));
    e->id        = engram_new_id();
    e->from_id   = el_strdup(self_id);
    e->to_id     = el_strdup(peer_node);
    e->relation  = el_strdup("dharma-relation");
    e->metadata  = el_strdup("{}");
    e->weight    = 0.0;
    e->confidence = 1.0;
    int64_t now  = engram_now_ms();
    e->created_at = now; e->updated_at = now;
    e->layer_id  = ENGRAM_LAYER_DEFAULT;
    int64_t idx = g->edge_count;
    g->edge_count++;
    return idx;
}

void dharma_strengthen(el_val_t cgi_id, el_val_t weight) {
    const char* id = EL_CSTR(cgi_id);
    if (!id || !*id) return;
    char* base = NULL; char* url = NULL;
    dharma_parse_id(id, &base, &url);
    free(url);
    int64_t ei = dharma_find_or_create_relation_edge(base, 1);
    free(base);
    if (ei < 0) return;
    EngramStore* g = engram_get();
    double inc = engram_decode_score(weight);
    if (!(inc >= 0.0)) inc = 0.0;
    double w = g->edges[ei].weight + inc;
    if (w < 0.0) w = 0.0;
    if (w > 1.0) w = 1.0;
    g->edges[ei].weight     = w;
    g->edges[ei].updated_at = engram_now_ms();
    g->edges[ei].last_fired = g->edges[ei].updated_at;
}

el_val_t dharma_relationship(el_val_t cgi_id) {
    const char* id = EL_CSTR(cgi_id);
    if (!id || !*id) return el_from_float(0.0);
    char* base = NULL; char* url = NULL;
    dharma_parse_id(id, &base, &url);
    free(url);
    int64_t ei = dharma_find_or_create_relation_edge(base, 0);
    free(base);
    if (ei < 0) return el_from_float(0.0);
    EngramStore* g = engram_get();
    return el_from_float(g->edges[ei].weight);
}

el_val_t dharma_peers(void) {
    /* Walk dharma-relation edges out of "dharma:self", weight > 0, sort desc. */
    EngramStore* g = engram_get();
    const char* self_id = "dharma:self";
    typedef struct { char* peer_base; double weight; } PeerEntry;
    PeerEntry* peers = malloc((size_t)(g->edge_count + 1) * sizeof(PeerEntry));
    int64_t pcount = 0;
    if (!peers) return el_list_empty();
    for (int64_t i = 0; i < g->edge_count; i++) {
        EngramEdge* e = &g->edges[i];
        if (!e->from_id || !e->to_id) continue;
        if (strcmp(e->from_id, self_id) != 0) continue;
        if (!e->relation || strcmp(e->relation, "dharma-relation") != 0) continue;
        if (e->weight <= 0.0) continue;
        const char* prefix = "dharma:peer:";
        size_t pl = strlen(prefix);
        if (strncmp(e->to_id, prefix, pl) != 0) continue;
        peers[pcount].peer_base = el_strdup(e->to_id + pl);
        peers[pcount].weight    = e->weight;
        pcount++;
    }
    /* Sort desc by weight. */
    for (int64_t i = 1; i < pcount; i++) {
        PeerEntry key = peers[i];
        int64_t j = i - 1;
        while (j >= 0 && peers[j].weight < key.weight) {
            peers[j + 1] = peers[j]; j--;
        }
        peers[j + 1] = key;
    }
    el_val_t out = el_list_empty();
    for (int64_t i = 0; i < pcount; i++) {
        out = el_list_append(out, EL_STR(peers[i].peer_base));
    }
    free(peers);
    return out;
}
#endif /* HAVE_CURL — DHARMA network */

/* ── Batch 4: LLM (Anthropic API client) ─────────────────────────────────── */
/*
 * All LLM builtins call https://api.anthropic.com/v1/messages with the API
 * key from env ANTHROPIC_API_KEY. Default model is "claude-sonnet-4-5"
 * when the supplied model is empty/null.
 *
 * `llm_call_agentic` runs a real multi-turn tool_use/tool_result loop.
 * Tool handlers are registered with `llm_register_tool(name, fn_name)`,
 * which dlsym()s the named symbol. Each tool handler has the C signature
 *   el_val_t handler(el_val_t input_json);
 * and returns a JSON-string el_val_t result. Iteration is capped at 10.
 */

#ifdef HAVE_CURL
static const char* LLM_DEFAULT_MODEL = "claude-sonnet-4-5";
static const char* LLM_API_URL       = "https://api.anthropic.com/v1/messages";
static const char* LLM_VERSION       = "2023-06-01";

static const char* llm_resolve_model(const char* m) {
    if (!m || !*m) return LLM_DEFAULT_MODEL;
    return m;
}

/*
 * ── Configurable LLM provider chain ──────────────────────────────────────────
 *
 * Providers are configured via indexed env vars. The runtime tries each in
 * order (0, 1, 2, ...) and returns the first successful non-empty response.
 *
 * Per provider (N = 0, 1, 2, ...):
 *   NEURON_LLM_N_URL    — endpoint URL (base URL; /v1/chat/completions appended
 *                          if format is "openai" and not already in URL)
 *   NEURON_LLM_N_KEY    — API key
 *   NEURON_LLM_N_FORMAT — "openai" (default) or "anthropic"
 *   NEURON_LLM_N_MODEL  — model name override (optional)
 *
 * Example — Neuron inference primary, Anthropic fallback:
 *   NEURON_LLM_0_URL=https://soma.../v1/chat/completions
 *   NEURON_LLM_0_KEY=svc-key
 *   NEURON_LLM_0_FORMAT=openai
 *   NEURON_LLM_0_MODEL=neuron
 *   NEURON_LLM_1_URL=https://api.anthropic.com/v1/messages
 *   NEURON_LLM_1_KEY=sk-ant-...
 *   NEURON_LLM_1_FORMAT=anthropic
 *
 * If no NEURON_LLM_0_URL is set, falls back to legacy ANTHROPIC_API_KEY.
 */

#define LLM_MAX_PROVIDERS 16

/* forward declarations */
static el_val_t llm_extract_text(el_val_t resp_val);
static el_val_t llm_extract_text_openai(el_val_t resp_val);

static el_val_t llm_extract_text_openai(el_val_t resp_val) {
    const char* resp = EL_CSTR(resp_val);
    if (!resp || !*resp) return el_wrap_str(el_strdup(""));
    if (resp[0] == '{' && strstr(resp, "\"error\"")) return el_wrap_str(el_strdup(""));
    const char* choices = json_find_key(resp, "choices");
    if (!choices || *choices != '[') return el_wrap_str(el_strdup(""));
    choices++;
    while (*choices == ' ' || *choices == '\t') choices++;
    if (*choices != '{') return el_wrap_str(el_strdup(""));
    const char* end = json_skip_value(choices);
    size_t n = (size_t)(end - choices);
    char* obj = malloc(n + 1); memcpy(obj, choices, n); obj[n] = '\0';
    const char* msg = json_find_key(obj, "message");
    if (!msg || *msg != '{') { free(obj); return el_wrap_str(el_strdup("")); }
    const char* msg_end = json_skip_value(msg);
    size_t mn = (size_t)(msg_end - msg);
    char* msg_obj = malloc(mn + 1); memcpy(msg_obj, msg, mn); msg_obj[mn] = '\0';
    const char* content = json_find_key(msg_obj, "content");
    el_val_t result = el_wrap_str(el_strdup(""));
    if (content && *content == '"') {
        JsonParser jp = { .p = content, .end = content + strlen(content), .err = 0 };
        char* text = jp_parse_string_raw(&jp);
        if (!jp.err && text) result = el_wrap_str(text);
    }
    free(msg_obj); free(obj);
    return result;
}

/* Send a request to one provider. Returns the raw response string.
 * format: 0 = openai, 1 = anthropic */
static el_val_t llm_provider_request(const char* url, const char* key,
                                      int format, const char* model,
                                      const char* system_str,
                                      const char* user_str) {
    char* esc_sys  = system_str && *system_str ? json_escape_alloc(system_str) : NULL;
    char* esc_user = json_escape_alloc(user_str ? user_str : "");
    JsonBuf b; jb_init(&b);
    struct curl_slist* h = NULL;
    h = curl_slist_append(h, "Content-Type: application/json");

    if (format == 0) { /* OpenAI */
        char full_url[1024];
        if (strstr(url, "/chat/completions") || strstr(url, "/messages")) {
            snprintf(full_url, sizeof(full_url), "%s", url);
        } else {
            snprintf(full_url, sizeof(full_url), "%s/v1/chat/completions", url);
        }
        { size_t n = strlen(key)+24; char* l=malloc(n); snprintf(l,n,"Authorization: Bearer %s",key); h=curl_slist_append(h,l); free(l); }
        jb_putc(&b, '{');
        jb_puts(&b, "\"model\":"); jb_emit_escaped(&b, model ? model : "neuron");
        jb_puts(&b, ",\"max_tokens\":4096,\"messages\":[");
        if (esc_sys && *esc_sys) { jb_puts(&b,"{\"role\":\"system\",\"content\":\""); jb_puts(&b,esc_sys); jb_puts(&b,"\"},"); }
        jb_puts(&b, "{\"role\":\"user\",\"content\":\""); jb_puts(&b, esc_user); jb_puts(&b, "\"}]}");
        el_val_t resp = http_do("POST", full_url, b.buf, h);
        curl_slist_free_all(h); free(b.buf);
        if (esc_sys) free(esc_sys); free(esc_user);
        return llm_extract_text_openai(resp);
    } else { /* Anthropic */
        { size_t n = strlen(key)+16; char* l=malloc(n); snprintf(l,n,"x-api-key: %s",key); h=curl_slist_append(h,l); free(l); }
        { size_t n = strlen(LLM_VERSION)+32; char* l=malloc(n); snprintf(l,n,"anthropic-version: %s",LLM_VERSION); h=curl_slist_append(h,l); free(l); }
        jb_putc(&b, '{');
        jb_puts(&b, "\"model\":"); jb_emit_escaped(&b, model ? model : LLM_DEFAULT_MODEL);
        jb_puts(&b, ",\"max_tokens\":4096");
        if (esc_sys && *esc_sys) { jb_puts(&b,",\"system\":\""); jb_puts(&b,esc_sys); jb_puts(&b,"\""); }
        jb_puts(&b, ",\"messages\":[{\"role\":\"user\",\"content\":\""); jb_puts(&b, esc_user); jb_puts(&b, "\"}]}");
        el_val_t resp = http_do("POST", url, b.buf, h);
        curl_slist_free_all(h); free(b.buf);
        if (esc_sys) free(esc_sys); free(esc_user);
        return llm_extract_text(resp);
    }
}

static el_val_t llm_chain_call(const char* system_str, const char* user_str) {
    char url_key[64], key_key[64], fmt_key[64], model_key[64];
    for (int i = 0; i < LLM_MAX_PROVIDERS; i++) {
        snprintf(url_key,   sizeof(url_key),   "NEURON_LLM_%d_URL",    i);
        snprintf(key_key,   sizeof(key_key),   "NEURON_LLM_%d_KEY",    i);
        snprintf(fmt_key,   sizeof(fmt_key),   "NEURON_LLM_%d_FORMAT", i);
        snprintf(model_key, sizeof(model_key), "NEURON_LLM_%d_MODEL",  i);
        const char* url   = getenv(url_key);
        const char* key   = getenv(key_key);
        if (!url || !*url || !key || !*key) break; /* end of chain */
        const char* fmt_s = getenv(fmt_key);
        int fmt = (fmt_s && strcmp(fmt_s, "anthropic") == 0) ? 1 : 0;
        const char* model = getenv(model_key);
        fprintf(stderr, "[llm] trying provider %d (%s)\n", i, url);
        el_val_t result = llm_provider_request(url, key, fmt, model, system_str, user_str);
        const char* t = EL_CSTR(result);
        if (t && *t && t[0] != '{') return result; /* success */
        fprintf(stderr, "[llm] provider %d failed or empty, trying next\n", i);
    }
    /* Legacy fallback: ANTHROPIC_API_KEY */
    const char* api_key = getenv("ANTHROPIC_API_KEY");
    if (!api_key || !*api_key) return http_error_json("no LLM providers configured");
    fprintf(stderr, "[llm] using legacy ANTHROPIC_API_KEY fallback\n");
    return llm_provider_request(LLM_API_URL, api_key, 1, NULL, system_str, user_str);
}

/* Legacy llm_request — kept for backward compat with agentic loop internals */
static el_val_t llm_request(const char* json_body) {
    const char* api_key = getenv("ANTHROPIC_API_KEY");
    if (!api_key || !*api_key) return http_error_json("ANTHROPIC_API_KEY not set");
    struct curl_slist* h = NULL;
    h = curl_slist_append(h, "Content-Type: application/json");
    { size_t n=strlen(api_key)+16; char* l=malloc(n); snprintf(l,n,"x-api-key: %s",api_key); h=curl_slist_append(h,l); free(l); }
    { size_t n=strlen(LLM_VERSION)+32; char* l=malloc(n); snprintf(l,n,"anthropic-version: %s",LLM_VERSION); h=curl_slist_append(h,l); free(l); }
    el_val_t resp = http_do("POST", LLM_API_URL, json_body, h);
    curl_slist_free_all(h);
    return resp;
}

/* Extract concatenated assistant text from an Anthropic /v1/messages
 * response. The response shape is:
 *   {"content":[{"type":"text","text":"..."}, ...], ...}
 * If parsing fails, returns the raw response so the caller can inspect.
 */
static el_val_t llm_extract_text(el_val_t resp_val) {
    const char* resp = EL_CSTR(resp_val);
    if (!resp || !*resp) return el_wrap_str(el_strdup(""));
    /* If error JSON, propagate as-is. */
    if (resp[0] == '{' && strstr(resp, "\"error\"")) {
        return el_wrap_str(el_strdup(resp));
    }
    /* Find "content":[ ... ] */
    const char* p = json_find_key(resp, "content");
    if (!p) return el_wrap_str(el_strdup(resp));
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (*p != '[') return el_wrap_str(el_strdup(resp));
    p++;
    JsonBuf out; jb_init(&out);
    while (*p && *p != ']') {
        while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r' || *p == ',') p++;
        if (*p != '{') break;
        const char* end = json_skip_value(p);
        size_t n = (size_t)(end - p);
        char* obj = malloc(n + 1);
        memcpy(obj, p, n); obj[n] = '\0';
        const char* type_p = json_find_key(obj, "type");
        if (type_p && *type_p == '"') {
            JsonParser jp = { .p = type_p, .end = type_p + strlen(type_p), .err = 0 };
            char* type_s = jp_parse_string_raw(&jp);
            if (!jp.err && type_s && strcmp(type_s, "text") == 0) {
                const char* tp = json_find_key(obj, "text");
                if (tp && *tp == '"') {
                    JsonParser jp2 = { .p = tp, .end = tp + strlen(tp), .err = 0 };
                    char* text_s = jp_parse_string_raw(&jp2);
                    if (!jp2.err && text_s) jb_puts(&out, text_s);
                    free(text_s);
                }
            }
            free(type_s);
        }
        free(obj);
        p = end;
    }
    return el_wrap_str(out.buf);
}

el_val_t llm_call(el_val_t model, el_val_t prompt) {
    const char* u = EL_CSTR(prompt); if (!u) u = "";
    return llm_chain_call(NULL, u);
}

el_val_t llm_call_system(el_val_t model, el_val_t system_prompt, el_val_t user_prompt) {
    const char* s = EL_CSTR(system_prompt); if (!s) s = "";
    const char* u = EL_CSTR(user_prompt);   if (!u) u = "";
    return llm_chain_call(s, u);
}

/* ── Tool registry for llm_call_agentic ─────────────────────────────────── */

typedef el_val_t (*llm_tool_fn)(el_val_t input);

typedef struct LlmToolEntry {
    char* name;
    llm_tool_fn fn;
} LlmToolEntry;

static LlmToolEntry  _llm_tools[64];
static size_t        _llm_tool_count = 0;
static pthread_mutex_t _llm_tool_mu = PTHREAD_MUTEX_INITIALIZER;

static llm_tool_fn llm_tool_lookup(const char* name) {
    if (!name) return NULL;
    llm_tool_fn fn = NULL;
    pthread_mutex_lock(&_llm_tool_mu);
    for (size_t i = 0; i < _llm_tool_count; i++) {
        if (strcmp(_llm_tools[i].name, name) == 0) { fn = _llm_tools[i].fn; break; }
    }
    pthread_mutex_unlock(&_llm_tool_mu);
    return fn;
}

void llm_register_tool(el_val_t name, el_val_t handler_fn_name) {
    const char* nm  = EL_CSTR(name);
    const char* sym = EL_CSTR(handler_fn_name);
    if (!nm || !*nm || !sym || !*sym) return;
    void* p = dlsym(RTLD_DEFAULT, sym);
    if (!p) {
        fprintf(stderr, "[llm_register_tool] symbol not found: %s\n", sym);
        return;
    }
    pthread_mutex_lock(&_llm_tool_mu);
    /* Replace existing entry by name. */
    for (size_t i = 0; i < _llm_tool_count; i++) {
        if (strcmp(_llm_tools[i].name, nm) == 0) {
            _llm_tools[i].fn = (llm_tool_fn)p;
            pthread_mutex_unlock(&_llm_tool_mu);
            return;
        }
    }
    if (_llm_tool_count < sizeof(_llm_tools) / sizeof(_llm_tools[0])) {
        _llm_tools[_llm_tool_count].name = el_strdup(nm);
        _llm_tools[_llm_tool_count].fn   = (llm_tool_fn)p;
        _llm_tool_count++;
    }
    pthread_mutex_unlock(&_llm_tool_mu);
}

/* Serialize the El `tools` list into the JSON `tools:[...]` field expected
 * by the Anthropic API. Each tool is an ElMap with name/description/
 * input_schema. input_schema is treated as either a JSON-object string
 * (passed through verbatim) or a missing field (substitute {}).         */
static void llm_emit_tools_json(JsonBuf* b, el_val_t tools_list) {
    jb_putc(b, '[');
    ElList* lst = (ElList*)(uintptr_t)tools_list;
    int64_t n = lst ? lst->length : 0;
    for (int64_t i = 0; i < n; i++) {
        if (i > 0) jb_putc(b, ',');
        ElMap* tm = as_map(lst->elems[i]);
        const char* name = "";
        const char* desc = "";
        const char* schema = "{}";
        if (tm) {
            for (int64_t k = 0; k < tm->count; k++) {
                const char* key = EL_CSTR(tm->keys[k]);
                const char* val = EL_CSTR(tm->values[k]);
                if (!key || !val) continue;
                if (strcmp(key, "name") == 0) name = val;
                else if (strcmp(key, "description") == 0) desc = val;
                else if (strcmp(key, "input_schema") == 0) schema = val;
            }
        }
        char* esc_name = json_escape_alloc(name);
        char* esc_desc = json_escape_alloc(desc);
        jb_puts(b, "{\"name\":\"");        jb_puts(b, esc_name);
        jb_puts(b, "\",\"description\":\""); jb_puts(b, esc_desc);
        jb_puts(b, "\",\"input_schema\":");  jb_puts(b, schema && *schema ? schema : "{}");
        jb_putc(b, '}');
        free(esc_name); free(esc_desc);
    }
    jb_putc(b, ']');
}

/* Walk the assistant `content` array and emit each block back into b,
 * preserving the verbatim JSON of every block — used to re-include the
 * assistant turn in the next request.                                 */
static void llm_emit_content_blocks(JsonBuf* b, const char* resp) {
    const char* p = json_find_key(resp, "content");
    jb_putc(b, '[');
    if (!p) { jb_putc(b, ']'); return; }
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (*p != '[') { jb_putc(b, ']'); return; }
    p++;
    int first = 1;
    while (*p && *p != ']') {
        while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r' || *p == ',') p++;
        if (*p != '{') break;
        const char* end = json_skip_value(p);
        if (!first) jb_putc(b, ',');
        first = 0;
        size_t n = (size_t)(end - p);
        jb_reserve(b, n);
        memcpy(b->buf + b->len, p, n);
        b->len += n;
        b->buf[b->len] = '\0';
        p = end;
    }
    jb_putc(b, ']');
}

/* Concatenate all "text" blocks from a response. Returns owned string. */
static char* llm_concat_text_blocks(const char* resp) {
    JsonBuf out; jb_init(&out);
    if (!resp) return out.buf;
    const char* p = json_find_key(resp, "content");
    if (!p) return out.buf;
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (*p != '[') return out.buf;
    p++;
    while (*p && *p != ']') {
        while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r' || *p == ',') p++;
        if (*p != '{') break;
        const char* end = json_skip_value(p);
        size_t n = (size_t)(end - p);
        char* obj = malloc(n + 1);
        memcpy(obj, p, n); obj[n] = '\0';
        const char* tp = json_find_key(obj, "type");
        if (tp && *tp == '"') {
            JsonParser jp = { .p = tp, .end = tp + strlen(tp), .err = 0 };
            char* tname = jp_parse_string_raw(&jp);
            if (!jp.err && tname && strcmp(tname, "text") == 0) {
                const char* xp = json_find_key(obj, "text");
                if (xp && *xp == '"') {
                    JsonParser jp2 = { .p = xp, .end = xp + strlen(xp), .err = 0 };
                    char* txt = jp_parse_string_raw(&jp2);
                    if (!jp2.err && txt) jb_puts(&out, txt);
                    free(txt);
                }
            }
            free(tname);
        }
        free(obj);
        p = end;
    }
    return out.buf;
}

/* Build tool_result message blocks for every tool_use in a response.
 * Appends to `b` an array element for each tool_use; caller wraps. */
static int llm_build_tool_results(JsonBuf* b, const char* resp) {
    int any = 0;
    const char* p = json_find_key(resp, "content");
    if (!p) return 0;
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (*p != '[') return 0;
    p++;
    while (*p && *p != ']') {
        while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r' || *p == ',') p++;
        if (*p != '{') break;
        const char* end = json_skip_value(p);
        size_t n = (size_t)(end - p);
        char* obj = malloc(n + 1);
        memcpy(obj, p, n); obj[n] = '\0';

        const char* tp = json_find_key(obj, "type");
        char* type_s = NULL;
        if (tp && *tp == '"') {
            JsonParser jp = { .p = tp, .end = tp + strlen(tp), .err = 0 };
            type_s = jp_parse_string_raw(&jp);
        }
        if (type_s && strcmp(type_s, "tool_use") == 0) {
            /* Extract id, name, input. */
            char* id_s = NULL; char* name_s = NULL;
            const char* idp = json_find_key(obj, "id");
            if (idp && *idp == '"') {
                JsonParser jp = { .p = idp, .end = idp + strlen(idp), .err = 0 };
                id_s = jp_parse_string_raw(&jp);
            }
            const char* np = json_find_key(obj, "name");
            if (np && *np == '"') {
                JsonParser jp = { .p = np, .end = np + strlen(np), .err = 0 };
                name_s = jp_parse_string_raw(&jp);
            }
            el_val_t input_raw = json_get_raw(EL_STR(obj), EL_STR("input"));
            const char* input_s = EL_CSTR(input_raw);
            if (!input_s || !*input_s) input_s = "{}";

            llm_tool_fn fn = llm_tool_lookup(name_s ? name_s : "");
            char* result = NULL;
            int is_error = 0;
            if (!fn) {
                size_t en = strlen(name_s ? name_s : "(null)") + 64;
                result = malloc(en);
                snprintf(result, en, "{\"error\":\"tool not registered: %s\"}",
                         name_s ? name_s : "(null)");
                is_error = 1;
            } else {
                el_val_t out = fn(EL_STR(input_s));
                const char* os = EL_CSTR(out);
                result = el_strdup(os ? os : "");
            }

            if (any) jb_putc(b, ',');
            char* esc_id = json_escape_alloc(id_s ? id_s : "");
            char* esc_res = json_escape_alloc(result ? result : "");
            jb_puts(b, "{\"type\":\"tool_result\",\"tool_use_id\":\"");
            jb_puts(b, esc_id);
            jb_puts(b, "\",\"content\":\"");
            jb_puts(b, esc_res);
            jb_puts(b, "\"");
            if (is_error) jb_puts(b, ",\"is_error\":true");
            jb_putc(b, '}');
            free(esc_id); free(esc_res); free(result);
            free(id_s); free(name_s);
            any = 1;
        }
        free(type_s);
        free(obj);
        p = end;
    }
    return any;
}

el_val_t llm_call_agentic(el_val_t model, el_val_t system, el_val_t user, el_val_t tools) {
    /* Empty tools list → degrade to plain system call. */
    ElList* tl = (ElList*)(uintptr_t)tools;
    if (!tl || tl->length == 0) {
        return llm_call_system(model, system, user);
    }
    const char* m = llm_resolve_model(EL_CSTR(model));
    const char* sys_p = EL_CSTR(system); if (!sys_p) sys_p = "";
    const char* usr_p = EL_CSTR(user);   if (!usr_p) usr_p = "";

    /* Build the static parts: tools JSON and system prompt — these don't
     * change across iterations.                                         */
    JsonBuf tools_buf; jb_init(&tools_buf);
    llm_emit_tools_json(&tools_buf, tools);
    char* esc_sys = json_escape_alloc(sys_p);

    /* messages array, accumulated as a mutable JSON fragment (no surrounding
     * brackets — emitted at request time).                                 */
    JsonBuf msgs; jb_init(&msgs);
    /* First user message. */
    char* esc_user = json_escape_alloc(usr_p);
    jb_puts(&msgs, "{\"role\":\"user\",\"content\":\"");
    jb_puts(&msgs, esc_user);
    jb_puts(&msgs, "\"}");
    free(esc_user);

    char* last_text = el_strdup("");
    el_val_t final_out = 0;
    int reached_cap = 1;

    for (int iter = 0; iter < 10; iter++) {
        /* Build request body. */
        JsonBuf body; jb_init(&body);
        jb_putc(&body, '{');
        jb_puts(&body, "\"model\":"); jb_emit_escaped(&body, m);
        jb_puts(&body, ",\"max_tokens\":4096");
        if (*sys_p) {
            jb_puts(&body, ",\"system\":\"");
            jb_puts(&body, esc_sys);
            jb_puts(&body, "\"");
        }
        jb_puts(&body, ",\"tools\":");
        jb_puts(&body, tools_buf.buf);
        jb_puts(&body, ",\"messages\":[");
        jb_puts(&body, msgs.buf);
        jb_puts(&body, "]}");

        el_val_t resp_v = llm_request(body.buf);
        free(body.buf);
        const char* resp = EL_CSTR(resp_v);
        if (!resp || !*resp) {
            final_out = http_error_json("empty response");
            reached_cap = 0;
            break;
        }
        if (resp[0] == '{' && strstr(resp, "\"error\"") &&
            !json_find_key(resp, "content")) {
            final_out = el_wrap_str(el_strdup(resp));
            reached_cap = 0;
            break;
        }

        /* Update last_text from this response. */
        free(last_text);
        last_text = llm_concat_text_blocks(resp);

        /* Inspect stop_reason. */
        el_val_t sr_v = json_get_string(EL_STR(resp), EL_STR("stop_reason"));
        const char* sr = EL_CSTR(sr_v); if (!sr) sr = "";

        if (strcmp(sr, "end_turn") == 0) {
            final_out = el_wrap_str(el_strdup(last_text));
            reached_cap = 0;
            break;
        }
        if (strcmp(sr, "max_tokens") == 0) {
            size_t ln = strlen(last_text) + 16;
            char* out = malloc(ln);
            snprintf(out, ln, "%s\n[truncated]", last_text);
            final_out = el_wrap_str(out);
            reached_cap = 0;
            break;
        }
        if (strcmp(sr, "tool_use") != 0) {
            /* Unexpected stop reason; return the text we have. */
            final_out = el_wrap_str(el_strdup(last_text));
            reached_cap = 0;
            break;
        }

        /* Append the assistant turn (raw content blocks) to messages. */
        JsonBuf ab; jb_init(&ab);
        jb_puts(&ab, ",{\"role\":\"assistant\",\"content\":");
        llm_emit_content_blocks(&ab, resp);
        jb_putc(&ab, '}');
        jb_puts(&msgs, ab.buf);
        free(ab.buf);

        /* Build tool_result message. */
        JsonBuf tr; jb_init(&tr);
        jb_puts(&tr, ",{\"role\":\"user\",\"content\":[");
        int any = llm_build_tool_results(&tr, resp);
        jb_puts(&tr, "]}");
        if (any) {
            jb_puts(&msgs, tr.buf);
        }
        free(tr.buf);
    }

    if (reached_cap) {
        size_t ln = strlen(last_text) + 32;
        char* out = malloc(ln);
        snprintf(out, ln, "[loop_cap_reached]\n%s", last_text);
        final_out = el_wrap_str(out);
    }
    free(last_text);
    free(esc_sys);
    free(tools_buf.buf);
    free(msgs.buf);
    return final_out;
}

/* base64-encode arbitrary bytes (returns owned C string).
 * Internal helper for llm_vision; the public crypto entry point that El
 * programs call is `base64_encode(el_val_t)` defined in the crypto block
 * at the end of this file. */
static char* el_b64_encode_internal(const unsigned char* src, size_t n) {
    static const char tbl[] =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    size_t out_len = 4 * ((n + 2) / 3);
    char* out = malloc(out_len + 1);
    if (!out) return NULL;
    size_t o = 0;
    for (size_t i = 0; i < n;) {
        uint32_t v = 0; int got = 0;
        v |= (uint32_t)src[i++] << 16; got++;
        if (i < n) { v |= (uint32_t)src[i++] << 8;  got++; }
        if (i < n) { v |= (uint32_t)src[i++];        got++; }
        out[o++] = tbl[(v >> 18) & 0x3f];
        out[o++] = tbl[(v >> 12) & 0x3f];
        out[o++] = (got > 1) ? tbl[(v >> 6) & 0x3f] : '=';
        out[o++] = (got > 2) ? tbl[v & 0x3f]        : '=';
    }
    out[o] = '\0';
    return out;
}

el_val_t llm_vision(el_val_t model, el_val_t system, el_val_t prompt, el_val_t image_url_or_b64) {
    const char* m = llm_resolve_model(EL_CSTR(model));
    const char* s = EL_CSTR(system); if (!s) s = "";
    const char* u = EL_CSTR(prompt); if (!u) u = "";
    const char* img = EL_CSTR(image_url_or_b64); if (!img) img = "";

    /* Choose source mode */
    char* image_block = NULL;
    if (strncasecmp(img, "http://", 7) == 0 || strncasecmp(img, "https://", 8) == 0) {
        char* esc_url = json_escape_alloc(img);
        size_t n = strlen(esc_url) + 128;
        image_block = malloc(n);
        snprintf(image_block, n,
                 "{\"type\":\"image\",\"source\":{\"type\":\"url\",\"url\":\"%s\"}}",
                 esc_url);
        free(esc_url);
    } else if (strncmp(img, "data:", 5) == 0) {
        /* Inline data URL: split media-type and base64 */
        const char* semi = strchr(img + 5, ';');
        const char* comma = strchr(img + 5, ',');
        char media[64] = "image/png";
        if (semi && comma && semi < comma) {
            size_t ml = (size_t)(semi - (img + 5));
            if (ml >= sizeof(media)) ml = sizeof(media) - 1;
            memcpy(media, img + 5, ml); media[ml] = '\0';
        }
        const char* b64 = comma ? comma + 1 : "";
        char* esc_media = json_escape_alloc(media);
        char* esc_b64   = json_escape_alloc(b64);
        size_t n = strlen(esc_media) + strlen(esc_b64) + 192;
        image_block = malloc(n);
        snprintf(image_block, n,
                 "{\"type\":\"image\",\"source\":{\"type\":\"base64\","
                 "\"media_type\":\"%s\",\"data\":\"%s\"}}",
                 esc_media, esc_b64);
        free(esc_media); free(esc_b64);
    } else if (*img) {
        /* Treat as file path: read, base64-encode, attach. */
        FILE* f = fopen(img, "rb");
        if (!f) {
            char err[256]; snprintf(err, sizeof(err), "cannot open image: %s", img);
            return http_error_json(err);
        }
        fseek(f, 0, SEEK_END);
        long sz = ftell(f);
        rewind(f);
        if (sz <= 0) { fclose(f); return http_error_json("empty image file"); }
        unsigned char* buf = malloc((size_t)sz);
        if (!buf) { fclose(f); return http_error_json("oom"); }
        size_t got = fread(buf, 1, (size_t)sz, f);
        fclose(f);
        char* b64 = el_b64_encode_internal(buf, got);
        free(buf);
        if (!b64) return http_error_json("base64 encode failed");
        const char* media = "image/png";
        size_t ilen = strlen(img);
        if (ilen >= 4) {
            if (strcasecmp(img + ilen - 4, ".jpg") == 0 ||
                (ilen >= 5 && strcasecmp(img + ilen - 5, ".jpeg") == 0)) media = "image/jpeg";
            else if (strcasecmp(img + ilen - 4, ".gif") == 0) media = "image/gif";
            else if (strcasecmp(img + ilen - 4, ".webp") == 0) media = "image/webp";
        }
        char* esc_b64 = json_escape_alloc(b64); free(b64);
        size_t n = strlen(esc_b64) + 192;
        image_block = malloc(n);
        snprintf(image_block, n,
                 "{\"type\":\"image\",\"source\":{\"type\":\"base64\","
                 "\"media_type\":\"%s\",\"data\":\"%s\"}}",
                 media, esc_b64);
        free(esc_b64);
    }

    char* esc_sys  = json_escape_alloc(s);
    char* esc_user = json_escape_alloc(u);
    JsonBuf b; jb_init(&b);
    jb_putc(&b, '{');
    jb_puts(&b, "\"model\":"); jb_emit_escaped(&b, m);
    jb_puts(&b, ",\"max_tokens\":4096");
    if (*s) {
        jb_puts(&b, ",\"system\":\"");
        jb_puts(&b, esc_sys);
        jb_puts(&b, "\"");
    }
    jb_puts(&b, ",\"messages\":[{\"role\":\"user\",\"content\":[");
    if (image_block) {
        jb_puts(&b, image_block);
        jb_putc(&b, ',');
    }
    jb_puts(&b, "{\"type\":\"text\",\"text\":\"");
    jb_puts(&b, esc_user);
    jb_puts(&b, "\"}]}]}");
    free(esc_sys); free(esc_user); free(image_block);
    el_val_t resp = llm_request(b.buf);
    free(b.buf);
    return llm_extract_text(resp);
}

el_val_t llm_models(void) {
    el_val_t lst = el_list_empty();
    lst = el_list_append(lst, el_wrap_str(el_strdup("claude-sonnet-4-5")));
    lst = el_list_append(lst, el_wrap_str(el_strdup("claude-opus-4-7")));
    lst = el_list_append(lst, el_wrap_str(el_strdup("claude-haiku-4-5")));
    return lst;
}
#endif /* HAVE_CURL */

/* ── Native VM builtin aliases ──────────────────────────────────────────────
 * El source files use native_* names (El VM builtins).
 * When compiled to C, these map directly to el_* runtime functions. */

el_val_t native_list_get(el_val_t list, el_val_t index) {
    return el_list_get(list, index);
}

el_val_t native_list_len(el_val_t list) {
    return el_list_len(list);
}

el_val_t native_list_append(el_val_t list, el_val_t elem) {
    return el_list_append(list, elem);
}

el_val_t native_list_empty(void) {
    return el_list_empty();
}

el_val_t native_list_clone(el_val_t list) {
    return el_list_clone(list);
}

el_val_t native_string_chars(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    el_val_t result = el_list_empty();
    if (!s) return result;
    while (*s) {
        char buf[2];
        buf[0] = *s;
        buf[1] = '\0';
        result = el_list_append(result, EL_STR(strdup(buf)));
        s++;
    }
    return result;
}

el_val_t native_int_to_str(el_val_t n) {
    return int_to_str(n);
}

/* ── Method-call shorthand aliases ──────────────────────────────────────────
 * Short names that result from the method-call convention:
 *   myList.append(x) → append(myList, x)
 *   myList.len()     → len(myList)
 *   myList.get(i)    → get(myList, i)
 *   myMap.map_get(k) → map_get(myMap, k)
 *   myMap.map_set(k,v) → map_set(myMap, k, v)                              */

el_val_t append(el_val_t list, el_val_t elem)  { return el_list_append(list, elem); }
el_val_t len(el_val_t list)                    { return el_list_len(list); }
el_val_t get(el_val_t list, el_val_t index)    { return el_list_get(list, index); }
el_val_t map_get(el_val_t map, el_val_t key)   { return el_map_get(map, key); }
el_val_t map_set(el_val_t map, el_val_t key, el_val_t value) { return el_map_set(map, key, value); }

/* ── Crypto primitives ──────────────────────────────────────────────────────
 *
 * SHA-256 implementation adapted from Brad Conte's public-domain reference
 * (https://github.com/B-Con/crypto-algorithms/blob/master/sha256.c, public
 * domain per the project's LICENSE). HMAC follows RFC 2104. Base64 encoding
 * follows RFC 4648; the URL-safe variant uses the alphabet from §5 of the
 * RFC and omits padding (per JWT/JWS convention).
 *
 * Self-contained: no OpenSSL/libcrypto dependency. The runtime keeps its
 * existing `-lcurl -lpthread -ldl -lm` link line.
 *
 * Binary outputs (sha256_bytes, hmac_sha256_bytes) tag their buffer with a
 * magic header so base64_encode/base64url_encode can recover the exact byte
 * length even when the payload contains embedded NULs. Plain C strings
 * (without the header) fall back to strlen(), preserving the existing API
 * shape for normal text inputs.                                              */

/* Magic-header for length-tagged binary buffers. Layout:
 *   [ uint32_t magic = EL_MAGIC_BIN ][ uint32_t length ][ data... ][ \0 ]
 * The returned el_val_t points at `data`, so consumers that strlen() it still
 * get a sensible (though possibly truncated) view. el_bin_len() recovers the
 * true length by sniffing the 8 bytes preceding the pointer.
 *
 * Magic value chosen with high MSB so it cannot collide with printable ASCII
 * (the same discriminator pattern used by EL_MAGIC_LIST / EL_MAGIC_MAP). */
#define EL_MAGIC_BIN 0xE1B17EAFu

typedef struct {
    uint32_t magic;
    uint32_t length;
} el_bin_hdr_t;

/* Allocate a length-tagged binary buffer; returns pointer to the data area. */
static unsigned char* el_bin_alloc(size_t len) {
    el_bin_hdr_t* hdr = (el_bin_hdr_t*)malloc(sizeof(el_bin_hdr_t) + len + 1);
    if (!hdr) { fputs("el_runtime: out of memory (bin)\n", stderr); exit(1); }
    hdr->magic = EL_MAGIC_BIN;
    hdr->length = (uint32_t)len;
    unsigned char* data = (unsigned char*)(hdr + 1);
    data[len] = '\0';   /* keep NUL-terminated for accidental strlen calls */
    return data;
}

/* Recover length from a possibly-tagged buffer. Returns 1 if tagged. */
static int el_bin_lookup(const void* p, size_t* out_len) {
    if (!p) { *out_len = 0; return 0; }
    /* Avoid reading off the front of a page on tiny pointers (e.g. NULs
     * passed in as int-cast values). 4096 is a safe lower bound on any
     * platform we target.                                              */
    if ((uintptr_t)p < 4096) return 0;
    const el_bin_hdr_t* hdr = (const el_bin_hdr_t*)((const char*)p - sizeof(el_bin_hdr_t));
    if (hdr->magic != EL_MAGIC_BIN) return 0;
    *out_len = hdr->length;
    return 1;
}

/* Effective input length: tagged length if present, else strlen. */
static size_t el_input_len(const char* s) {
    size_t n;
    if (el_bin_lookup(s, &n)) return n;
    return s ? strlen(s) : 0;
}

/* ─── SHA-256 (Brad Conte / public domain) ──────────────────────────────── */

typedef struct {
    unsigned char data[64];
    uint32_t      datalen;
    uint64_t      bitlen;
    uint32_t      state[8];
} el_sha256_ctx_t;

static const uint32_t el_sha256_k[64] = {
    0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
    0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
    0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
    0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
    0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
    0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
    0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
    0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
};

#define EL_ROTR(x, n) (((x) >> (n)) | ((x) << (32 - (n))))
#define EL_CH(x,y,z)  (((x) & (y)) ^ (~(x) & (z)))
#define EL_MAJ(x,y,z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
#define EL_EP0(x)     (EL_ROTR(x,2)  ^ EL_ROTR(x,13) ^ EL_ROTR(x,22))
#define EL_EP1(x)     (EL_ROTR(x,6)  ^ EL_ROTR(x,11) ^ EL_ROTR(x,25))
#define EL_SIG0(x)    (EL_ROTR(x,7)  ^ EL_ROTR(x,18) ^ ((x) >> 3))
#define EL_SIG1(x)    (EL_ROTR(x,17) ^ EL_ROTR(x,19) ^ ((x) >> 10))

static void el_sha256_transform(el_sha256_ctx_t* ctx, const unsigned char* data) {
    uint32_t a, b, c, d, e, f, g, h, t1, t2, m[64];
    int i, j;
    for (i = 0, j = 0; i < 16; ++i, j += 4) {
        m[i] = ((uint32_t)data[j] << 24) | ((uint32_t)data[j + 1] << 16)
             | ((uint32_t)data[j + 2] << 8) | (uint32_t)data[j + 3];
    }
    for (; i < 64; ++i) {
        m[i] = EL_SIG1(m[i-2]) + m[i-7] + EL_SIG0(m[i-15]) + m[i-16];
    }
    a = ctx->state[0]; b = ctx->state[1]; c = ctx->state[2]; d = ctx->state[3];
    e = ctx->state[4]; f = ctx->state[5]; g = ctx->state[6]; h = ctx->state[7];
    for (i = 0; i < 64; ++i) {
        t1 = h + EL_EP1(e) + EL_CH(e,f,g) + el_sha256_k[i] + m[i];
        t2 = EL_EP0(a) + EL_MAJ(a,b,c);
        h = g; g = f; f = e; e = d + t1; d = c; c = b; b = a; a = t1 + t2;
    }
    ctx->state[0] += a; ctx->state[1] += b; ctx->state[2] += c; ctx->state[3] += d;
    ctx->state[4] += e; ctx->state[5] += f; ctx->state[6] += g; ctx->state[7] += h;
}

static void el_sha256_init(el_sha256_ctx_t* ctx) {
    ctx->datalen = 0;
    ctx->bitlen = 0;
    ctx->state[0] = 0x6a09e667; ctx->state[1] = 0xbb67ae85;
    ctx->state[2] = 0x3c6ef372; ctx->state[3] = 0xa54ff53a;
    ctx->state[4] = 0x510e527f; ctx->state[5] = 0x9b05688c;
    ctx->state[6] = 0x1f83d9ab; ctx->state[7] = 0x5be0cd19;
}

static void el_sha256_update(el_sha256_ctx_t* ctx, const unsigned char* data, size_t len) {
    for (size_t i = 0; i < len; ++i) {
        ctx->data[ctx->datalen++] = data[i];
        if (ctx->datalen == 64) {
            el_sha256_transform(ctx, ctx->data);
            ctx->bitlen += 512;
            ctx->datalen = 0;
        }
    }
}

static void el_sha256_final(el_sha256_ctx_t* ctx, unsigned char hash[32]) {
    uint32_t i = ctx->datalen;
    if (ctx->datalen < 56) {
        ctx->data[i++] = 0x80;
        while (i < 56) ctx->data[i++] = 0x00;
    } else {
        ctx->data[i++] = 0x80;
        while (i < 64) ctx->data[i++] = 0x00;
        el_sha256_transform(ctx, ctx->data);
        memset(ctx->data, 0, 56);
    }
    ctx->bitlen += (uint64_t)ctx->datalen * 8;
    ctx->data[63] = (unsigned char)( ctx->bitlen        & 0xff);
    ctx->data[62] = (unsigned char)((ctx->bitlen >> 8)  & 0xff);
    ctx->data[61] = (unsigned char)((ctx->bitlen >> 16) & 0xff);
    ctx->data[60] = (unsigned char)((ctx->bitlen >> 24) & 0xff);
    ctx->data[59] = (unsigned char)((ctx->bitlen >> 32) & 0xff);
    ctx->data[58] = (unsigned char)((ctx->bitlen >> 40) & 0xff);
    ctx->data[57] = (unsigned char)((ctx->bitlen >> 48) & 0xff);
    ctx->data[56] = (unsigned char)((ctx->bitlen >> 56) & 0xff);
    el_sha256_transform(ctx, ctx->data);
    for (i = 0; i < 4; ++i) {
        hash[i]      = (ctx->state[0] >> (24 - i * 8)) & 0xff;
        hash[i +  4] = (ctx->state[1] >> (24 - i * 8)) & 0xff;
        hash[i +  8] = (ctx->state[2] >> (24 - i * 8)) & 0xff;
        hash[i + 12] = (ctx->state[3] >> (24 - i * 8)) & 0xff;
        hash[i + 16] = (ctx->state[4] >> (24 - i * 8)) & 0xff;
        hash[i + 20] = (ctx->state[5] >> (24 - i * 8)) & 0xff;
        hash[i + 24] = (ctx->state[6] >> (24 - i * 8)) & 0xff;
        hash[i + 28] = (ctx->state[7] >> (24 - i * 8)) & 0xff;
    }
}

static void el_sha256_oneshot(const unsigned char* data, size_t len, unsigned char out[32]) {
    el_sha256_ctx_t c;
    el_sha256_init(&c);
    el_sha256_update(&c, data, len);
    el_sha256_final(&c, out);
}

/* ─── HMAC-SHA-256 (RFC 2104) ───────────────────────────────────────────── */

static void el_hmac_sha256(const unsigned char* key, size_t key_len,
                           const unsigned char* msg, size_t msg_len,
                           unsigned char out[32]) {
    unsigned char k[64];
    unsigned char k_ipad[64];
    unsigned char k_opad[64];
    unsigned char inner[32];

    if (key_len > 64) {
        el_sha256_oneshot(key, key_len, k);
        memset(k + 32, 0, 32);
    } else {
        memcpy(k, key, key_len);
        memset(k + key_len, 0, 64 - key_len);
    }
    for (int i = 0; i < 64; ++i) {
        k_ipad[i] = k[i] ^ 0x36;
        k_opad[i] = k[i] ^ 0x5c;
    }
    {
        el_sha256_ctx_t c;
        el_sha256_init(&c);
        el_sha256_update(&c, k_ipad, 64);
        el_sha256_update(&c, msg, msg_len);
        el_sha256_final(&c, inner);
    }
    {
        el_sha256_ctx_t c;
        el_sha256_init(&c);
        el_sha256_update(&c, k_opad, 64);
        el_sha256_update(&c, inner, 32);
        el_sha256_final(&c, out);
    }
}

/* ─── Hex helper ────────────────────────────────────────────────────────── */

static el_val_t el_hex_encode(const unsigned char* data, size_t len) {
    static const char digits[] = "0123456789abcdef";
    char* out = el_strbuf(len * 2);
    for (size_t i = 0; i < len; ++i) {
        out[i * 2]     = digits[(data[i] >> 4) & 0xf];
        out[i * 2 + 1] = digits[ data[i]       & 0xf];
    }
    out[len * 2] = '\0';
    return el_wrap_str(out);
}

/* ─── Base64 (RFC 4648) ─────────────────────────────────────────────────── */

static const char el_b64_std_alphabet[64] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
static const char el_b64_url_alphabet[64] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";

el_val_t el_base64_encode_n(const unsigned char* data, size_t len, int url_safe) {
    const char* alphabet = url_safe ? el_b64_url_alphabet : el_b64_std_alphabet;
    /* Standard form is padded to multiple of 4; URL-safe omits padding. */
    size_t out_cap = ((len + 2) / 3) * 4 + 1;
    char* out = el_strbuf(out_cap);
    size_t i = 0, j = 0;
    while (i + 3 <= len) {
        uint32_t v = ((uint32_t)data[i] << 16) | ((uint32_t)data[i+1] << 8) | (uint32_t)data[i+2];
        out[j++] = alphabet[(v >> 18) & 0x3f];
        out[j++] = alphabet[(v >> 12) & 0x3f];
        out[j++] = alphabet[(v >>  6) & 0x3f];
        out[j++] = alphabet[ v        & 0x3f];
        i += 3;
    }
    size_t rem = len - i;
    if (rem == 1) {
        uint32_t v = (uint32_t)data[i] << 16;
        out[j++] = alphabet[(v >> 18) & 0x3f];
        out[j++] = alphabet[(v >> 12) & 0x3f];
        if (!url_safe) { out[j++] = '='; out[j++] = '='; }
    } else if (rem == 2) {
        uint32_t v = ((uint32_t)data[i] << 16) | ((uint32_t)data[i+1] << 8);
        out[j++] = alphabet[(v >> 18) & 0x3f];
        out[j++] = alphabet[(v >> 12) & 0x3f];
        out[j++] = alphabet[(v >>  6) & 0x3f];
        if (!url_safe) { out[j++] = '='; }
    }
    out[j] = '\0';
    return el_wrap_str(out);
}

/* Decode either alphabet — accepts both '+/' and '-_' transparently, and
 * tolerates missing padding (which JWTs typically omit). Whitespace is
 * skipped for robustness. Invalid characters cause the decode to stop and
 * the partial result so far is returned. */
static el_val_t el_base64_decode_any(const char* in) {
    if (!in) {
        unsigned char* empty = el_bin_alloc(0);
        return EL_STR((char*)empty);
    }
    size_t in_len = strlen(in);
    /* Worst case: 3 output bytes per 4 input chars, +1 NUL slack. */
    unsigned char* out = el_bin_alloc(((in_len + 3) / 4) * 3 + 1);

    int8_t lut[256];
    for (int i = 0; i < 256; ++i) lut[i] = -1;
    for (int i = 0; i < 64; ++i) lut[(unsigned char)el_b64_std_alphabet[i]] = (int8_t)i;
    /* Allow URL-safe characters too (so one decoder handles both forms). */
    lut[(unsigned char)'-'] = 62;
    lut[(unsigned char)'_'] = 63;

    uint32_t buf  = 0;
    int      bits = 0;
    size_t   o    = 0;
    for (size_t i = 0; i < in_len; ++i) {
        unsigned char c = (unsigned char)in[i];
        if (c == '=' || c == '\r' || c == '\n' || c == ' ' || c == '\t') continue;
        int8_t v = lut[c];
        if (v < 0) break;   /* invalid char — stop */
        buf = (buf << 6) | (uint32_t)v;
        bits += 6;
        if (bits >= 8) {
            bits -= 8;
            out[o++] = (unsigned char)((buf >> bits) & 0xff);
        }
    }
    /* Patch the length header to the actual decoded length. */
    el_bin_hdr_t* hdr = (el_bin_hdr_t*)((char*)out - sizeof(el_bin_hdr_t));
    hdr->length = (uint32_t)o;
    out[o] = '\0';
    return EL_STR((char*)out);
}

/* ─── Public crypto entry points ────────────────────────────────────────── */

el_val_t el_sha256_bytes_n(const unsigned char* data, size_t len) {
    unsigned char* out = el_bin_alloc(32);
    el_sha256_oneshot(data, len, out);
    return EL_STR((char*)out);
}

el_val_t sha256_hex(el_val_t input) {
    const char* s = EL_CSTR(input);
    size_t n = el_input_len(s);
    unsigned char digest[32];
    el_sha256_oneshot((const unsigned char*)(s ? s : ""), n, digest);
    return el_hex_encode(digest, 32);
}

el_val_t sha256_bytes(el_val_t input) {
    const char* s = EL_CSTR(input);
    size_t n = el_input_len(s);
    return el_sha256_bytes_n((const unsigned char*)(s ? s : ""), n);
}

el_val_t hmac_sha256_hex(el_val_t key, el_val_t message) {
    const char* k = EL_CSTR(key);
    const char* m = EL_CSTR(message);
    size_t kn = el_input_len(k);
    size_t mn = el_input_len(m);
    unsigned char mac[32];
    el_hmac_sha256((const unsigned char*)(k ? k : ""), kn,
                   (const unsigned char*)(m ? m : ""), mn,
                   mac);
    return el_hex_encode(mac, 32);
}

el_val_t hmac_sha256_bytes(el_val_t key, el_val_t message) {
    const char* k = EL_CSTR(key);
    const char* m = EL_CSTR(message);
    size_t kn = el_input_len(k);
    size_t mn = el_input_len(m);
    unsigned char* out = el_bin_alloc(32);
    el_hmac_sha256((const unsigned char*)(k ? k : ""), kn,
                   (const unsigned char*)(m ? m : ""), mn,
                   out);
    return EL_STR((char*)out);
}

el_val_t base64_encode(el_val_t input) {
    const char* s = EL_CSTR(input);
    size_t n = el_input_len(s);
    return el_base64_encode_n((const unsigned char*)(s ? s : ""), n, /*url_safe=*/0);
}

el_val_t base64url_encode(el_val_t input) {
    const char* s = EL_CSTR(input);
    size_t n = el_input_len(s);
    return el_base64_encode_n((const unsigned char*)(s ? s : ""), n, /*url_safe=*/1);
}

el_val_t base64_decode(el_val_t input) {
    return el_base64_decode_any(EL_CSTR(input));
}

el_val_t base64url_decode(el_val_t input) {
    return el_base64_decode_any(EL_CSTR(input));
}

/* ── Post-quantum cryptography (liboqs + OpenSSL) ───────────────────────────
 *
 * Algorithm choices (per CNSA 2.0 / NIST PQ guidance, as of 2024):
 *   Signatures: CRYSTALS-Dilithium-3   (NIST security level 3, balanced)
 *   KEM:        CRYSTALS-Kyber-768     (NIST security level 3)
 *   Hash:       SHA3-256 (Keccak)      (PQ-aware protocols favour SHA3 over SHA2)
 *   Hybrid:     X25519 || Kyber-768, combined via HKDF-SHA256
 *
 * Why hybrid: Kyber is new. X25519 has 20+ years of analysis. Hybridizing
 * preserves classical security if Kyber falls to a future cryptanalytic
 * advance, and preserves PQ security if X25519 falls to a quantum adversary.
 * "Recordable now, decryptable later" already threatens long-lived classical
 * key exchange — the only safe move for keys protecting durable doctrine
 * (CGI lineage, KindredGrants, Principal-CGI covenants) is to encapsulate
 * with PQ today, even if the classical leg is what the wire shows.
 *
 * Compile-time detection: when <oqs/oqs.h> is unavailable the pq_* functions
 * compile to stubs that return a JSON error envelope. SHA3-256 stays
 * available regardless (it's implemented inline, no liboqs dep). This lets
 * the runtime build cleanly on dev machines without liboqs while production
 * gets the full PQ stack.                                                    */

/* ─── SHA3-256 (Keccak, FIPS 202) ────────────────────────────────────────────
 * Inline reference implementation. ~120 LoC, no external dependency.
 * rate=1088 bits, capacity=512 bits, output=256 bits, padding=0x06.          */

static const uint64_t el_keccak_rc[24] = {
    0x0000000000000001ULL, 0x0000000000008082ULL, 0x800000000000808aULL,
    0x8000000080008000ULL, 0x000000000000808bULL, 0x0000000080000001ULL,
    0x8000000080008081ULL, 0x8000000000008009ULL, 0x000000000000008aULL,
    0x0000000000000088ULL, 0x0000000080008009ULL, 0x000000008000000aULL,
    0x000000008000808bULL, 0x800000000000008bULL, 0x8000000000008089ULL,
    0x8000000000008003ULL, 0x8000000000008002ULL, 0x8000000000000080ULL,
    0x000000000000800aULL, 0x800000008000000aULL, 0x8000000080008081ULL,
    0x8000000000008080ULL, 0x0000000080000001ULL, 0x8000000080008008ULL
};

static const unsigned el_keccak_rho[24] = {
     1,  3,  6, 10, 15, 21, 28, 36, 45, 55,  2, 14,
    27, 41, 56,  8, 25, 43, 62, 18, 39, 61, 20, 44
};

static const unsigned el_keccak_pi[24] = {
    10,  7, 11, 17, 18,  3,  5, 16,  8, 21, 24,  4,
    15, 23, 19, 13, 12,  2, 20, 14, 22,  9,  6,  1
};

#define EL_ROTL64(x, n) (((x) << (n)) | ((x) >> (64 - (n))))

static void el_keccak_f1600(uint64_t s[25]) {
    for (int round = 0; round < 24; ++round) {
        uint64_t bc[5], t;
        for (int i = 0; i < 5; ++i)
            bc[i] = s[i] ^ s[i+5] ^ s[i+10] ^ s[i+15] ^ s[i+20];
        for (int i = 0; i < 5; ++i) {
            t = bc[(i+4) % 5] ^ EL_ROTL64(bc[(i+1) % 5], 1);
            for (int j = 0; j < 25; j += 5) s[j+i] ^= t;
        }
        t = s[1];
        for (int i = 0; i < 24; ++i) {
            int j = el_keccak_pi[i];
            bc[0] = s[j];
            s[j]  = EL_ROTL64(t, el_keccak_rho[i]);
            t = bc[0];
        }
        for (int j = 0; j < 25; j += 5) {
            for (int i = 0; i < 5; ++i) bc[i] = s[j+i];
            for (int i = 0; i < 5; ++i)
                s[j+i] = bc[i] ^ ((~bc[(i+1) % 5]) & bc[(i+2) % 5]);
        }
        s[0] ^= el_keccak_rc[round];
    }
}

static void el_sha3_256_oneshot(const unsigned char* data, size_t len,
                                unsigned char out[32]) {
    uint64_t st[25] = {0};
    unsigned char* sb = (unsigned char*)st;
    const size_t rate = 136;   /* 1088 bits / 8 */
    size_t i = 0;
    while (len - i >= rate) {
        for (size_t k = 0; k < rate; ++k) sb[k] ^= data[i + k];
        el_keccak_f1600(st);
        i += rate;
    }
    size_t rem = len - i;
    for (size_t k = 0; k < rem; ++k) sb[k] ^= data[i + k];
    sb[rem]      ^= 0x06;   /* SHA3 domain-separation byte */
    sb[rate - 1] ^= 0x80;   /* final-block padding bit (high bit of last byte) */
    el_keccak_f1600(st);
    memcpy(out, sb, 32);
}

el_val_t sha3_256_hex(el_val_t input) {
    const char* s = EL_CSTR(input);
    size_t n = el_input_len(s);
    unsigned char digest[32];
    el_sha3_256_oneshot((const unsigned char*)(s ? s : ""), n, digest);
    return el_hex_encode(digest, 32);
}

/* ─── Hex decode helper ─────────────────────────────────────────────────────
 * Returns a length-tagged binary buffer (so embedded NULs survive); on
 * odd-length / invalid input returns NULL with *out_len = 0. Caller is
 * responsible for emitting the error envelope.                               */

static int el_hex_nibble(char c) {
    if (c >= '0' && c <= '9') return c - '0';
    if (c >= 'a' && c <= 'f') return c - 'a' + 10;
    if (c >= 'A' && c <= 'F') return c - 'A' + 10;
    return -1;
}

__attribute__((unused))
static unsigned char* el_hex_decode(const char* s, size_t* out_len) {
    *out_len = 0;
    if (!s) return NULL;
    size_t n = strlen(s);
    if (n & 1) return NULL;
    size_t blen = n / 2;
    unsigned char* out = el_bin_alloc(blen);
    for (size_t i = 0; i < blen; ++i) {
        int hi = el_hex_nibble(s[i*2]);
        int lo = el_hex_nibble(s[i*2 + 1]);
        if (hi < 0 || lo < 0) return NULL;
        out[i] = (unsigned char)((hi << 4) | lo);
    }
    *out_len = blen;
    return out;
}

/* JSON error envelope reused across all PQ entry points. */
static el_val_t pq_error(const char* msg) {
    return http_error_json(msg);
}

#if __has_include(<oqs/oqs.h>)
#include <oqs/oqs.h>
#define EL_HAVE_LIBOQS 1
#else
#define EL_HAVE_LIBOQS 0
#endif

#if EL_HAVE_LIBOQS && __has_include(<openssl/evp.h>)
#include <openssl/evp.h>
#define EL_HAVE_OPENSSL 1
#else
#define EL_HAVE_OPENSSL 0
#endif

#if !EL_HAVE_LIBOQS

/* ─── Stubs (liboqs unavailable) ───────────────────────────────────────────
 * Each entry point returns the same JSON error so callers can inspect a
 * single canonical "missing primitive" string. pq_verify is the lone
 * exception — verifying without liboqs simply means "not verified", so
 * returning Bool false (0) keeps the type contract intact.                  */

#define EL_PQ_NO_LIB "liboqs not linked, post-quantum primitives unavailable"

el_val_t pq_keygen_signature(void)                            { return pq_error(EL_PQ_NO_LIB); }
el_val_t pq_sign(el_val_t sk, el_val_t msg)                   { (void)sk; (void)msg; return pq_error(EL_PQ_NO_LIB); }
el_val_t pq_verify(el_val_t pk, el_val_t msg, el_val_t sig)   { (void)pk; (void)msg; (void)sig; return EL_INT(0); }
el_val_t pq_kem_keygen(void)                                  { return pq_error(EL_PQ_NO_LIB); }
el_val_t pq_kem_encaps(el_val_t pk)                           { (void)pk; return pq_error(EL_PQ_NO_LIB); }
el_val_t pq_kem_decaps(el_val_t sk, el_val_t ct)              { (void)sk; (void)ct; return pq_error(EL_PQ_NO_LIB); }
el_val_t pq_hybrid_keygen(void)                               { return pq_error(EL_PQ_NO_LIB); }
el_val_t pq_hybrid_handshake(el_val_t pub)                    { (void)pub; return pq_error(EL_PQ_NO_LIB); }

#else  /* EL_HAVE_LIBOQS */

/* ─── Dilithium-3 / ML-DSA-65 signatures ────────────────────────────────
 *
 * NIST FIPS 204 standardized CRYSTALS-Dilithium as ML-DSA. ML-DSA-65 is the
 * FIPS form of what we historically called Dilithium-3 — same algorithm
 * family, same security level, identical key/sig sizes, but with a couple
 * of standardization-driven tweaks (e.g. domain separation in the message
 * binding). liboqs 0.12+ exposes both names; 0.15+ retired the legacy
 * "Dilithium" constants in favour of "ML-DSA". We prefer ML-DSA-65 if the
 * header advertises it, fall back to Dilithium-3 otherwise. Anything
 * already signed with the older constant remains verifiable against that
 * same constant — callers should pin the algorithm via the OQS_SIG handle's
 * method_name field if they need to interoperate with archival signatures. */

#if defined(OQS_SIG_alg_ml_dsa_65)
#  define EL_DILITHIUM_ALG OQS_SIG_alg_ml_dsa_65
#elif defined(OQS_SIG_alg_dilithium_3)
#  define EL_DILITHIUM_ALG OQS_SIG_alg_dilithium_3
#else
#  define EL_DILITHIUM_ALG "ML-DSA-65"   /* string fallback; runtime probe catches misconfig */
#endif

el_val_t pq_keygen_signature(void) {
    OQS_SIG* sig = OQS_SIG_new(EL_DILITHIUM_ALG);
    if (!sig) return pq_error("OQS_SIG_new(dilithium-3) failed");
    unsigned char* pk = (unsigned char*)malloc(sig->length_public_key);
    unsigned char* sk = (unsigned char*)malloc(sig->length_secret_key);
    if (!pk || !sk) { free(pk); free(sk); OQS_SIG_free(sig); return pq_error("oom"); }
    if (OQS_SIG_keypair(sig, pk, sk) != OQS_SUCCESS) {
        free(pk); free(sk); OQS_SIG_free(sig);
        return pq_error("dilithium-3 keypair generation failed");
    }
    el_val_t pk_hex = el_hex_encode(pk, sig->length_public_key);
    el_val_t sk_hex = el_hex_encode(sk, sig->length_secret_key);
    OQS_MEM_secure_free(sk, sig->length_secret_key);
    free(pk);

    const char* pks = EL_CSTR(pk_hex);
    const char* sks = EL_CSTR(sk_hex);
    char* buf = el_strbuf(strlen(pks) + strlen(sks) + 64);
    sprintf(buf, "{\"public_key\":\"%s\",\"secret_key\":\"%s\"}", pks, sks);
    OQS_SIG_free(sig);
    return el_wrap_str(buf);
}

el_val_t pq_sign(el_val_t secret_key_hex, el_val_t message) {
    size_t sk_len = 0;
    unsigned char* sk = el_hex_decode(EL_CSTR(secret_key_hex), &sk_len);
    if (!sk) return pq_error("invalid hex in secret_key");

    OQS_SIG* sig = OQS_SIG_new(EL_DILITHIUM_ALG);
    if (!sig) return pq_error("OQS_SIG_new(dilithium-3) failed");
    if (sk_len != sig->length_secret_key) {
        OQS_SIG_free(sig);
        return pq_error("secret_key length mismatch for dilithium-3");
    }

    const char* msg = EL_CSTR(message);
    size_t msg_len = el_input_len(msg);
    unsigned char* signature = (unsigned char*)malloc(sig->length_signature);
    size_t signature_len = sig->length_signature;
    if (!signature) { OQS_SIG_free(sig); return pq_error("oom"); }

    if (OQS_SIG_sign(sig, signature, &signature_len,
                     (const unsigned char*)(msg ? msg : ""), msg_len, sk) != OQS_SUCCESS) {
        free(signature); OQS_SIG_free(sig);
        return pq_error("dilithium-3 sign failed");
    }
    el_val_t sig_hex = el_hex_encode(signature, signature_len);
    free(signature); OQS_SIG_free(sig);
    return sig_hex;
}

el_val_t pq_verify(el_val_t public_key_hex, el_val_t message, el_val_t signature_hex) {
    size_t pk_len = 0, sig_len = 0;
    unsigned char* pk = el_hex_decode(EL_CSTR(public_key_hex), &pk_len);
    unsigned char* signature = el_hex_decode(EL_CSTR(signature_hex), &sig_len);
    if (!pk || !signature) return EL_INT(0);

    OQS_SIG* sig = OQS_SIG_new(EL_DILITHIUM_ALG);
    if (!sig) return EL_INT(0);
    if (pk_len != sig->length_public_key) { OQS_SIG_free(sig); return EL_INT(0); }

    const char* msg = EL_CSTR(message);
    size_t msg_len = el_input_len(msg);
    OQS_STATUS rc = OQS_SIG_verify(sig,
                                   (const unsigned char*)(msg ? msg : ""), msg_len,
                                   signature, sig_len, pk);
    OQS_SIG_free(sig);
    return (rc == OQS_SUCCESS) ? EL_INT(1) : EL_INT(0);
}

/* ─── Kyber-768 / ML-KEM-768 KEM ────────────────────────────────────────
 *
 * NIST FIPS 203 standardized CRYSTALS-Kyber as ML-KEM. ML-KEM-768 is the
 * FIPS form of what we historically called Kyber-768. Same situation as
 * Dilithium → ML-DSA: prefer the standardized constant, fall back to the
 * legacy name. liboqs 0.15.0 still exposes OQS_KEM_alg_kyber_768; the
 * algorithm is identical at the wire level to ML-KEM-768 except for FIPS
 * domain-separation tweaks, so the two ciphertexts/keys are NOT
 * cross-compatible. Pin the constant for archival material. */

#if defined(OQS_KEM_alg_ml_kem_768)
#  define EL_KYBER_ALG OQS_KEM_alg_ml_kem_768
#elif defined(OQS_KEM_alg_kyber_768)
#  define EL_KYBER_ALG OQS_KEM_alg_kyber_768
#else
#  define EL_KYBER_ALG "ML-KEM-768"
#endif

el_val_t pq_kem_keygen(void) {
    OQS_KEM* kem = OQS_KEM_new(EL_KYBER_ALG);
    if (!kem) return pq_error("OQS_KEM_new(kyber-768) failed");
    unsigned char* pk = (unsigned char*)malloc(kem->length_public_key);
    unsigned char* sk = (unsigned char*)malloc(kem->length_secret_key);
    if (!pk || !sk) { free(pk); free(sk); OQS_KEM_free(kem); return pq_error("oom"); }
    if (OQS_KEM_keypair(kem, pk, sk) != OQS_SUCCESS) {
        free(pk); free(sk); OQS_KEM_free(kem);
        return pq_error("kyber-768 keypair generation failed");
    }
    el_val_t pk_hex = el_hex_encode(pk, kem->length_public_key);
    el_val_t sk_hex = el_hex_encode(sk, kem->length_secret_key);
    OQS_MEM_secure_free(sk, kem->length_secret_key);
    free(pk);

    const char* pks = EL_CSTR(pk_hex);
    const char* sks = EL_CSTR(sk_hex);
    char* buf = el_strbuf(strlen(pks) + strlen(sks) + 64);
    sprintf(buf, "{\"public_key\":\"%s\",\"secret_key\":\"%s\"}", pks, sks);
    OQS_KEM_free(kem);
    return el_wrap_str(buf);
}

el_val_t pq_kem_encaps(el_val_t public_key_hex) {
    size_t pk_len = 0;
    unsigned char* pk = el_hex_decode(EL_CSTR(public_key_hex), &pk_len);
    if (!pk) return pq_error("invalid hex in public_key");

    OQS_KEM* kem = OQS_KEM_new(EL_KYBER_ALG);
    if (!kem) return pq_error("OQS_KEM_new(kyber-768) failed");
    if (pk_len != kem->length_public_key) {
        OQS_KEM_free(kem);
        return pq_error("public_key length mismatch for kyber-768");
    }
    unsigned char* ct = (unsigned char*)malloc(kem->length_ciphertext);
    unsigned char* ss = (unsigned char*)malloc(kem->length_shared_secret);
    if (!ct || !ss) { free(ct); free(ss); OQS_KEM_free(kem); return pq_error("oom"); }
    if (OQS_KEM_encaps(kem, ct, ss, pk) != OQS_SUCCESS) {
        free(ct); free(ss); OQS_KEM_free(kem);
        return pq_error("kyber-768 encapsulation failed");
    }
    el_val_t ct_hex = el_hex_encode(ct, kem->length_ciphertext);
    el_val_t ss_hex = el_hex_encode(ss, kem->length_shared_secret);
    free(ct);
    OQS_MEM_secure_free(ss, kem->length_shared_secret);

    const char* cts = EL_CSTR(ct_hex);
    const char* sss = EL_CSTR(ss_hex);
    char* buf = el_strbuf(strlen(cts) + strlen(sss) + 64);
    sprintf(buf, "{\"ciphertext\":\"%s\",\"shared_secret\":\"%s\"}", cts, sss);
    OQS_KEM_free(kem);
    return el_wrap_str(buf);
}

el_val_t pq_kem_decaps(el_val_t secret_key_hex, el_val_t ciphertext_hex) {
    size_t sk_len = 0, ct_len = 0;
    unsigned char* sk = el_hex_decode(EL_CSTR(secret_key_hex), &sk_len);
    unsigned char* ct = el_hex_decode(EL_CSTR(ciphertext_hex), &ct_len);
    if (!sk || !ct) return pq_error("invalid hex in inputs");

    OQS_KEM* kem = OQS_KEM_new(EL_KYBER_ALG);
    if (!kem) return pq_error("OQS_KEM_new(kyber-768) failed");
    if (sk_len != kem->length_secret_key || ct_len != kem->length_ciphertext) {
        OQS_KEM_free(kem);
        return pq_error("input length mismatch for kyber-768");
    }
    unsigned char* ss = (unsigned char*)malloc(kem->length_shared_secret);
    if (!ss) { OQS_KEM_free(kem); return pq_error("oom"); }
    /* Kyber is IND-CCA via Fujisaki-Okamoto: decaps always returns *some*
     * shared_secret even on tampered ciphertext (an implicit-rejection value
     * derived from sk). Protocols MUST confirm the shared_secret matches via
     * a subsequent step (e.g. AEAD tag, key-confirmation MAC) — do not
     * assume decaps success implies authenticity. */
    if (OQS_KEM_decaps(kem, ss, ct, sk) != OQS_SUCCESS) {
        free(ss); OQS_KEM_free(kem);
        return pq_error("kyber-768 decapsulation failed");
    }
    el_val_t ss_hex = el_hex_encode(ss, kem->length_shared_secret);
    OQS_MEM_secure_free(ss, kem->length_shared_secret);
    OQS_KEM_free(kem);
    return ss_hex;
}

/* ─── Hybrid handshake (X25519 + Kyber-768, HKDF-SHA256 combined) ─────── */

#if !EL_HAVE_OPENSSL

el_val_t pq_hybrid_keygen(void) {
    return pq_error("hybrid handshake requires OpenSSL (X25519); rebuild with -lcrypto");
}
el_val_t pq_hybrid_handshake(el_val_t pub) {
    (void)pub;
    return pq_error("hybrid handshake requires OpenSSL (X25519); rebuild with -lcrypto");
}

#else  /* EL_HAVE_OPENSSL */

/* HKDF-SHA256 (RFC 5869) — Extract+Expand. Reuses the inline HMAC-SHA256
 * already in this file. Empty salt → 32 zero bytes per the RFC.            */
static void el_hkdf_sha256(const unsigned char* salt, size_t salt_len,
                           const unsigned char* ikm,  size_t ikm_len,
                           const unsigned char* info, size_t info_len,
                           unsigned char* out, size_t out_len) {
    unsigned char zero_salt[32] = {0};
    if (salt_len == 0) { salt = zero_salt; salt_len = 32; }
    unsigned char prk[32];
    el_hmac_sha256(salt, salt_len, ikm, ikm_len, prk);

    unsigned char t[32];
    size_t produced = 0;
    unsigned char counter = 1;
    unsigned char* buf = (unsigned char*)malloc(32 + info_len + 1);
    if (!buf) { fputs("el_runtime: hkdf oom\n", stderr); return; }
    while (produced < out_len) {
        size_t off = 0;
        if (counter > 1) { memcpy(buf, t, 32); off = 32; }
        if (info && info_len) { memcpy(buf + off, info, info_len); off += info_len; }
        buf[off++] = counter;
        el_hmac_sha256(prk, 32, buf, off, t);
        size_t chunk = (out_len - produced > 32) ? 32 : (out_len - produced);
        memcpy(out + produced, t, chunk);
        produced += chunk;
        counter++;
    }
    free(buf);
}

/* X25519 keygen via OpenSSL EVP. Returns 1 on success.
 * Fills pk[32] and sk[32] (raw X25519 byte strings, no DER wrapper). */
static int el_x25519_keygen(unsigned char pk[32], unsigned char sk[32]) {
    EVP_PKEY_CTX* pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_X25519, NULL);
    if (!pctx) return 0;
    if (EVP_PKEY_keygen_init(pctx) != 1) { EVP_PKEY_CTX_free(pctx); return 0; }
    EVP_PKEY* key = NULL;
    if (EVP_PKEY_keygen(pctx, &key) != 1) { EVP_PKEY_CTX_free(pctx); return 0; }
    EVP_PKEY_CTX_free(pctx);

    size_t plen = 32, slen = 32;
    if (EVP_PKEY_get_raw_public_key (key, pk, &plen) != 1 || plen != 32) {
        EVP_PKEY_free(key); return 0;
    }
    if (EVP_PKEY_get_raw_private_key(key, sk, &slen) != 1 || slen != 32) {
        EVP_PKEY_free(key); return 0;
    }
    EVP_PKEY_free(key);
    return 1;
}

/* X25519 ECDH: derive 32-byte shared secret from local sk and remote pk. */
static int el_x25519_derive(const unsigned char sk[32], const unsigned char rpk[32],
                            unsigned char ss[32]) {
    EVP_PKEY* my  = EVP_PKEY_new_raw_private_key(EVP_PKEY_X25519, NULL, sk, 32);
    EVP_PKEY* rem = EVP_PKEY_new_raw_public_key (EVP_PKEY_X25519, NULL, rpk, 32);
    if (!my || !rem) { EVP_PKEY_free(my); EVP_PKEY_free(rem); return 0; }
    EVP_PKEY_CTX* dctx = EVP_PKEY_CTX_new(my, NULL);
    if (!dctx) { EVP_PKEY_free(my); EVP_PKEY_free(rem); return 0; }
    int ok = 0;
    size_t out_len = 32;
    if (EVP_PKEY_derive_init(dctx) == 1 &&
        EVP_PKEY_derive_set_peer(dctx, rem) == 1 &&
        EVP_PKEY_derive(dctx, ss, &out_len) == 1 &&
        out_len == 32) ok = 1;
    EVP_PKEY_CTX_free(dctx);
    EVP_PKEY_free(my);
    EVP_PKEY_free(rem);
    return ok;
}

/* Hybrid wire layout (binary form, before hex encode):
 *   public_key  = x25519_pub (32) || kyber_pub (1184)         → 1216 bytes
 *   secret_key  = x25519_sec (32) || kyber_sec (2400)         → 2432 bytes
 *   ciphertext  = ephem_x25519_pub (32) || kyber_ct (1088)    → 1120 bytes
 *   shared_secret = HKDF-SHA256(x25519_ss || kyber_ss, info="el-pq-hybrid-v1", 32 bytes)
 * The keygen result also exposes the four component hex fields for callers
 * that prefer to handle the legs independently.                              */

el_val_t pq_hybrid_keygen(void) {
    OQS_KEM* kem = OQS_KEM_new(EL_KYBER_ALG);
    if (!kem) return pq_error("OQS_KEM_new(kyber-768) failed");

    unsigned char xpk[32], xsk[32];
    if (!el_x25519_keygen(xpk, xsk)) {
        OQS_KEM_free(kem);
        return pq_error("X25519 keygen failed");
    }

    unsigned char* kpk = (unsigned char*)malloc(kem->length_public_key);
    unsigned char* ksk = (unsigned char*)malloc(kem->length_secret_key);
    if (!kpk || !ksk) { free(kpk); free(ksk); OQS_KEM_free(kem); return pq_error("oom"); }
    if (OQS_KEM_keypair(kem, kpk, ksk) != OQS_SUCCESS) {
        free(kpk); free(ksk); OQS_KEM_free(kem);
        return pq_error("kyber-768 keypair generation failed");
    }

    size_t pub_len = 32 + kem->length_public_key;
    size_t sec_len = 32 + kem->length_secret_key;
    unsigned char* pub_buf = (unsigned char*)malloc(pub_len);
    unsigned char* sec_buf = (unsigned char*)malloc(sec_len);
    if (!pub_buf || !sec_buf) {
        free(pub_buf); free(sec_buf); free(kpk);
        OQS_MEM_secure_free(ksk, kem->length_secret_key);
        OQS_KEM_free(kem); return pq_error("oom");
    }
    memcpy(pub_buf,      xpk, 32); memcpy(pub_buf + 32, kpk, kem->length_public_key);
    memcpy(sec_buf,      xsk, 32); memcpy(sec_buf + 32, ksk, kem->length_secret_key);

    el_val_t x_pub_hex = el_hex_encode(xpk, 32);
    el_val_t x_sec_hex = el_hex_encode(xsk, 32);
    el_val_t k_pub_hex = el_hex_encode(kpk, kem->length_public_key);
    el_val_t k_sec_hex = el_hex_encode(ksk, kem->length_secret_key);
    el_val_t pub_hex   = el_hex_encode(pub_buf, pub_len);
    el_val_t sec_hex   = el_hex_encode(sec_buf, sec_len);

    OQS_MEM_secure_free(ksk, kem->length_secret_key);
    free(kpk); free(pub_buf); free(sec_buf);
    OQS_KEM_free(kem);
    memset(xsk, 0, 32);   /* best-effort wipe of stack copy */

    const char* xph  = EL_CSTR(x_pub_hex);
    const char* xsh  = EL_CSTR(x_sec_hex);
    const char* kph  = EL_CSTR(k_pub_hex);
    const char* ksh  = EL_CSTR(k_sec_hex);
    const char* pubh = EL_CSTR(pub_hex);
    const char* sech = EL_CSTR(sec_hex);

    char* buf = el_strbuf(strlen(xph) + strlen(xsh) + strlen(kph) + strlen(ksh)
                          + strlen(pubh) + strlen(sech) + 256);
    sprintf(buf,
        "{\"x25519_pub\":\"%s\",\"x25519_sec\":\"%s\","
         "\"kyber_pub\":\"%s\",\"kyber_sec\":\"%s\","
         "\"public_key\":\"%s\",\"secret_key\":\"%s\"}",
        xph, xsh, kph, ksh, pubh, sech);
    return el_wrap_str(buf);
}

/* Initiator-side handshake. Caller supplies the responder's combined public
 * key (x25519_pub || kyber_pub, hex-encoded). The runtime:
 *   1. Generates an ephemeral X25519 keypair, runs ECDH against the
 *      responder's static x25519_pub.
 *   2. Runs Kyber-768 encaps against the responder's kyber_pub → kyber_ct,
 *      kyber_ss.
 *   3. Combined shared = HKDF-SHA256(salt="", ikm = x25519_ss || kyber_ss,
 *                                    info = "el-pq-hybrid-v1", L = 32).
 *   4. Returns combined ciphertext (= ephemeral_x25519_pub || kyber_ct) and
 *      the derived shared_secret.
 *
 * Responder side composition (intentionally not a separate runtime fn —
 * trivial to express in El given pq_kem_decaps + a future x25519_derive
 * primitive): split the ciphertext into ephem_xpk (32) and kyber_ct, run
 * X25519(static_xsk, ephem_xpk) and pq_kem_decaps(static_kyber_sk, kyber_ct),
 * then HKDF-SHA256 with the same salt/info to recover the same shared_secret.
 * If a separate x25519 entry point becomes valuable, add `pq_hybrid_open`
 * here taking (secret_key_combined, ciphertext_combined). */
el_val_t pq_hybrid_handshake(el_val_t remote_pub_combined) {
    size_t pub_len = 0;
    unsigned char* rpub = el_hex_decode(EL_CSTR(remote_pub_combined), &pub_len);
    if (!rpub) return pq_error("invalid hex in remote_pub_combined");

    OQS_KEM* kem = OQS_KEM_new(EL_KYBER_ALG);
    if (!kem) return pq_error("OQS_KEM_new(kyber-768) failed");
    if (pub_len != 32 + kem->length_public_key) {
        OQS_KEM_free(kem);
        return pq_error("remote_pub_combined length mismatch (expected x25519_pub || kyber_pub)");
    }

    unsigned char e_xpk[32], e_xsk[32], x_ss[32];
    if (!el_x25519_keygen(e_xpk, e_xsk)) {
        OQS_KEM_free(kem);
        return pq_error("X25519 ephemeral keygen failed");
    }
    if (!el_x25519_derive(e_xsk, rpub, x_ss)) {
        memset(e_xsk, 0, 32);
        OQS_KEM_free(kem);
        return pq_error("X25519 derive failed");
    }
    memset(e_xsk, 0, 32);   /* ephemeral; not needed after derive */

    unsigned char* k_ct = (unsigned char*)malloc(kem->length_ciphertext);
    unsigned char* k_ss = (unsigned char*)malloc(kem->length_shared_secret);
    if (!k_ct || !k_ss) {
        free(k_ct); free(k_ss); OQS_KEM_free(kem);
        return pq_error("oom");
    }
    if (OQS_KEM_encaps(kem, k_ct, k_ss, rpub + 32) != OQS_SUCCESS) {
        free(k_ct); free(k_ss); OQS_KEM_free(kem);
        return pq_error("kyber-768 encapsulation failed");
    }

    /* HKDF combine: ikm = x_ss || k_ss. */
    size_t ikm_len = 32 + kem->length_shared_secret;
    unsigned char* ikm = (unsigned char*)malloc(ikm_len);
    if (!ikm) {
        free(k_ct); OQS_MEM_secure_free(k_ss, kem->length_shared_secret);
        OQS_KEM_free(kem);
        return pq_error("oom");
    }
    memcpy(ikm,      x_ss, 32);
    memcpy(ikm + 32, k_ss, kem->length_shared_secret);
    unsigned char combined[32];
    static const char info_str[] = "el-pq-hybrid-v1";
    el_hkdf_sha256(NULL, 0, ikm, ikm_len,
                   (const unsigned char*)info_str, sizeof(info_str) - 1,
                   combined, 32);

    memset(x_ss, 0, 32);
    OQS_MEM_secure_free(k_ss, kem->length_shared_secret);
    OQS_MEM_secure_free(ikm,  ikm_len);

    /* Combined ciphertext = ephemeral_x25519_pub || kyber_ct. */
    size_t ct_len = 32 + kem->length_ciphertext;
    unsigned char* combined_ct = (unsigned char*)malloc(ct_len);
    if (!combined_ct) { free(k_ct); OQS_KEM_free(kem); return pq_error("oom"); }
    memcpy(combined_ct,      e_xpk, 32);
    memcpy(combined_ct + 32, k_ct,  kem->length_ciphertext);
    free(k_ct);
    OQS_KEM_free(kem);

    el_val_t ct_hex = el_hex_encode(combined_ct, ct_len);
    el_val_t ss_hex = el_hex_encode(combined, 32);
    free(combined_ct);
    memset(combined, 0, 32);

    const char* cts = EL_CSTR(ct_hex);
    const char* sss = EL_CSTR(ss_hex);
    char* buf = el_strbuf(strlen(cts) + strlen(sss) + 64);
    sprintf(buf, "{\"ciphertext\":\"%s\",\"shared_secret\":\"%s\"}", cts, sss);
    return el_wrap_str(buf);
}

#endif  /* EL_HAVE_OPENSSL */
#endif  /* EL_HAVE_LIBOQS */

/* ─── AEAD: AES-256-GCM ────────────────────────────────────────────────────
 *
 * Symmetric authenticated encryption used to wrap envelopes once a shared
 * secret has been derived from the KEM (Kyber-768 / hybrid). The El surface
 * is intentionally narrow:
 *
 *   aead_encrypt(key_hex, plaintext)
 *     → {"nonce":"<24 hex>","ciphertext":"<...hex including 16-byte tag>"}
 *
 *   aead_decrypt(key_hex, nonce_hex, ciphertext_hex)
 *     → plaintext String, or "" on auth failure / malformed input
 *
 * Conventions:
 *   - key_hex must decode to exactly 32 bytes (AES-256). Callers that hold
 *     a longer KEM shared_secret should normalize via SHA3-256(ss) → 32 bytes
 *     before passing it in. (Kyber-768's shared_secret is already 32 bytes,
 *     but keeping this contract explicit lets the El side be agnostic.)
 *   - nonce is a fresh 12-byte random value drawn from the OS CSPRNG. Caller
 *     never picks the nonce — eliminates the GCM nonce-reuse footgun entirely.
 *   - tag is the standard 16 bytes, appended to ciphertext per RFC 5116.
 *     `ciphertext` field is therefore (plaintext_len + 16) bytes, hex-encoded.
 *   - No associated data (AAD). If we later need bound metadata, add a
 *     length-prefixed AAD argument and bump the envelope version tag.
 *
 * Failure mode:
 *   aead_encrypt returns http_error_json(...) on input/system failure.
 *   aead_decrypt returns the empty string on ANY failure (including auth-tag
 *   mismatch). Callers MUST check for "" before using the result.            */

#if !__has_include(<openssl/evp.h>)

el_val_t aead_encrypt(el_val_t key_hex, el_val_t plaintext) {
    (void)key_hex; (void)plaintext;
    return http_error_json("aead_encrypt requires OpenSSL (libcrypto); rebuild with -lcrypto");
}
el_val_t aead_decrypt(el_val_t key_hex, el_val_t nonce_hex, el_val_t ciphertext_hex) {
    (void)key_hex; (void)nonce_hex; (void)ciphertext_hex;
    return el_wrap_str(el_strdup(""));
}

#else  /* OpenSSL available */

#include <openssl/evp.h>
#include <openssl/rand.h>

el_val_t aead_encrypt(el_val_t key_hex, el_val_t plaintext) {
    size_t key_len = 0;
    unsigned char* key = el_hex_decode(EL_CSTR(key_hex), &key_len);
    if (!key) return http_error_json("invalid hex in key");
    if (key_len != 32) return http_error_json("aead key must be 32 bytes (64 hex chars) for AES-256-GCM");

    const char* pt = EL_CSTR(plaintext);
    size_t pt_len = el_input_len(pt);
    if (!pt) pt = "";

    unsigned char nonce[12];
    if (RAND_bytes(nonce, 12) != 1) return http_error_json("OS CSPRNG failed (RAND_bytes)");

    EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
    if (!ctx) return http_error_json("EVP_CIPHER_CTX_new failed");

    if (EVP_EncryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL) != 1) {
        EVP_CIPHER_CTX_free(ctx); return http_error_json("aes-256-gcm init failed");
    }
    if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 12, NULL) != 1) {
        EVP_CIPHER_CTX_free(ctx); return http_error_json("set ivlen failed");
    }
    if (EVP_EncryptInit_ex(ctx, NULL, NULL, key, nonce) != 1) {
        EVP_CIPHER_CTX_free(ctx); return http_error_json("aes-256-gcm key/iv init failed");
    }

    /* GCM ciphertext is the same length as plaintext; we append a 16-byte
     * authentication tag for AEAD semantics. Allocate plaintext_len + 16. */
    unsigned char* ct = (unsigned char*)malloc(pt_len + 16);
    if (!ct) { EVP_CIPHER_CTX_free(ctx); return http_error_json("oom"); }
    int outlen = 0, total = 0;
    if (EVP_EncryptUpdate(ctx, ct, &outlen, (const unsigned char*)pt, (int)pt_len) != 1) {
        free(ct); EVP_CIPHER_CTX_free(ctx); return http_error_json("aes-256-gcm update failed");
    }
    total += outlen;
    if (EVP_EncryptFinal_ex(ctx, ct + total, &outlen) != 1) {
        free(ct); EVP_CIPHER_CTX_free(ctx); return http_error_json("aes-256-gcm final failed");
    }
    total += outlen;
    if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, 16, ct + total) != 1) {
        free(ct); EVP_CIPHER_CTX_free(ctx); return http_error_json("aes-256-gcm get tag failed");
    }
    EVP_CIPHER_CTX_free(ctx);

    el_val_t nonce_hex_v = el_hex_encode(nonce, 12);
    el_val_t ct_hex_v    = el_hex_encode(ct, (size_t)total + 16);
    free(ct);

    const char* nh = EL_CSTR(nonce_hex_v);
    const char* ch = EL_CSTR(ct_hex_v);
    char* buf = el_strbuf(strlen(nh) + strlen(ch) + 48);
    sprintf(buf, "{\"nonce\":\"%s\",\"ciphertext\":\"%s\"}", nh, ch);
    return el_wrap_str(buf);
}

el_val_t aead_decrypt(el_val_t key_hex, el_val_t nonce_hex, el_val_t ciphertext_hex) {
    size_t key_len = 0, nonce_len = 0, ct_len = 0;
    unsigned char* key   = el_hex_decode(EL_CSTR(key_hex),        &key_len);
    unsigned char* nonce = el_hex_decode(EL_CSTR(nonce_hex),      &nonce_len);
    unsigned char* ct    = el_hex_decode(EL_CSTR(ciphertext_hex), &ct_len);
    if (!key || !nonce || !ct)            return el_wrap_str(el_strdup(""));
    if (key_len != 32 || nonce_len != 12) return el_wrap_str(el_strdup(""));
    if (ct_len < 16)                      return el_wrap_str(el_strdup(""));

    size_t body_len = ct_len - 16;
    const unsigned char* tag  = ct + body_len;

    EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
    if (!ctx) return el_wrap_str(el_strdup(""));

    if (EVP_DecryptInit_ex(ctx, EVP_aes_256_gcm(), NULL, NULL, NULL) != 1 ||
        EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, 12, NULL) != 1   ||
        EVP_DecryptInit_ex(ctx, NULL, NULL, key, nonce) != 1) {
        EVP_CIPHER_CTX_free(ctx); return el_wrap_str(el_strdup(""));
    }

    unsigned char* pt = (unsigned char*)malloc(body_len + 1);
    if (!pt) { EVP_CIPHER_CTX_free(ctx); return el_wrap_str(el_strdup("")); }
    int outlen = 0, total = 0;
    if (EVP_DecryptUpdate(ctx, pt, &outlen, ct, (int)body_len) != 1) {
        free(pt); EVP_CIPHER_CTX_free(ctx); return el_wrap_str(el_strdup(""));
    }
    total += outlen;
    /* Set expected tag before final — GCM's final step is where auth happens. */
    if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, 16, (void*)tag) != 1) {
        free(pt); EVP_CIPHER_CTX_free(ctx); return el_wrap_str(el_strdup(""));
    }
    int rc = EVP_DecryptFinal_ex(ctx, pt + total, &outlen);
    EVP_CIPHER_CTX_free(ctx);
    if (rc != 1) {
        /* Auth failure or padding/length mismatch. Return empty so callers
         * cannot accidentally treat tampered ciphertext as a valid message. */
        free(pt);
        return el_wrap_str(el_strdup(""));
    }
    total += outlen;
    pt[total] = '\0';

    /* Copy into the el arena so the caller-visible string outlives this fn. */
    char* out = el_strbuf((size_t)total);
    memcpy(out, pt, (size_t)total);
    out[total] = '\0';
    free(pt);
    return el_wrap_str(out);
}

#endif  /* __has_include(<openssl/evp.h>) */

#ifdef HAVE_CURL
/* ────────────────────────────────────────────────────────────────────────────
 * OTLP/HTTP observability — logs, traces, metrics
 *
 * Design goals:
 *  - Zero blocking on the request path. Producers append to in-memory
 *    ring buffers; a single worker thread flushes to the OTLP endpoint.
 *  - Drop-on-failure semantics. If the endpoint is unreachable or slow,
 *    we drop telemetry rather than back-pressure into the request handler.
 *  - Best-effort serialization. Each record is pre-serialized as JSON when
 *    the El program calls the primitive; the worker just batches.
 *  - Configuration via env vars:
 *      OTLP_ENDPOINT       e.g. https://alloy.neuralplatform.ai:4318
 *      OTEL_SERVICE_NAME   e.g. neuron-web (default: argv[0] basename)
 *      OTEL_SERVICE_VERSION (default: "0.0.0")
 *      OTEL_RESOURCE_ATTRS  comma-sep k=v pairs (optional)
 *
 * Wire format: OTLP/HTTP JSON. Three endpoints:
 *      POST {endpoint}/v1/logs    — log records
 *      POST {endpoint}/v1/traces  — spans
 *      POST {endpoint}/v1/metrics — counter/gauge points
 *
 * El programs see four primitives:
 *      trace_span_start(name) -> SpanHandle      (just a string id)
 *      trace_span_end(handle)                    (computes duration, queues)
 *      emit_log(level, msg, fields_json)         (queues a log record)
 *      emit_metric(name, value, tags_json)       (queues a counter increment)
 * ────────────────────────────────────────────────────────────────────────────
 */

#define OTLP_BUF_CAP       4096   /* per-buffer ring size */
#define OTLP_FLUSH_MS      2000   /* flush every 2s */
#define OTLP_BATCH_MAX     200    /* up to 200 records per POST */

typedef struct {
    char*  data;       /* malloc'd JSON fragment for this record */
} OtlpRec;

typedef struct {
    OtlpRec  ring[OTLP_BUF_CAP];
    size_t   head;     /* next write slot */
    size_t   tail;     /* next read slot */
    pthread_mutex_t mu;
} OtlpQueue;

static OtlpQueue _otlp_logs   = { .mu = PTHREAD_MUTEX_INITIALIZER };
static OtlpQueue _otlp_traces = { .mu = PTHREAD_MUTEX_INITIALIZER };
static OtlpQueue _otlp_metrics = { .mu = PTHREAD_MUTEX_INITIALIZER };

static char*  _otlp_endpoint = NULL;       /* e.g. https://alloy.neuralplatform.ai:4318 */
static char*  _otlp_service_name = NULL;
static char*  _otlp_service_version = NULL;
static int    _otlp_initialized = 0;
static pthread_t _otlp_worker_thread;

/* enqueue — returns 1 if accepted, 0 if dropped (full buffer or no endpoint) */
static int otlp_enqueue(OtlpQueue* q, const char* json) {
    if (!_otlp_endpoint || !json) return 0;
    pthread_mutex_lock(&q->mu);
    size_t next_head = (q->head + 1) % OTLP_BUF_CAP;
    if (next_head == q->tail) {
        /* buffer full — drop oldest */
        free(q->ring[q->tail].data);
        q->ring[q->tail].data = NULL;
        q->tail = (q->tail + 1) % OTLP_BUF_CAP;
    }
    q->ring[q->head].data = strdup(json);
    q->head = next_head;
    pthread_mutex_unlock(&q->mu);
    return 1;
}

/* drain — copies up to OTLP_BATCH_MAX items into a comma-joined string,
 * caller must free the result. Returns NULL if queue is empty. */
static char* otlp_drain(OtlpQueue* q) {
    pthread_mutex_lock(&q->mu);
    if (q->head == q->tail) { pthread_mutex_unlock(&q->mu); return NULL; }
    /* compute total length */
    size_t total = 0, count = 0;
    size_t i = q->tail;
    while (i != q->head && count < OTLP_BATCH_MAX) {
        if (q->ring[i].data) total += strlen(q->ring[i].data) + 1; /* +1 for comma */
        i = (i + 1) % OTLP_BUF_CAP;
        count++;
    }
    char* out = malloc(total + 4);
    if (!out) { pthread_mutex_unlock(&q->mu); return NULL; }
    out[0] = '\0';
    size_t off = 0;
    i = q->tail;
    count = 0;
    while (i != q->head && count < OTLP_BATCH_MAX) {
        if (q->ring[i].data) {
            size_t l = strlen(q->ring[i].data);
            if (off > 0) { out[off++] = ','; }
            memcpy(out + off, q->ring[i].data, l);
            off += l;
            free(q->ring[i].data);
            q->ring[i].data = NULL;
        }
        i = (i + 1) % OTLP_BUF_CAP;
        count++;
    }
    out[off] = '\0';
    q->tail = i;
    pthread_mutex_unlock(&q->mu);
    return out;
}

/* Build resource block once (service.name, service.version, host.name) */
static char* otlp_resource_block(void) {
    static char cached[1024];
    static int built = 0;
    if (built) return cached;
    char host[256] = "unknown";
    gethostname(host, sizeof(host) - 1);
    snprintf(cached, sizeof(cached),
        "{\"attributes\":["
          "{\"key\":\"service.name\",\"value\":{\"stringValue\":\"%s\"}},"
          "{\"key\":\"service.version\",\"value\":{\"stringValue\":\"%s\"}},"
          "{\"key\":\"host.name\",\"value\":{\"stringValue\":\"%s\"}}"
        "]}",
        _otlp_service_name ? _otlp_service_name : "el-app",
        _otlp_service_version ? _otlp_service_version : "0.0.0",
        host);
    built = 1;
    return cached;
}

/* Best-effort POST. Drops on any error. */
static void otlp_post(const char* path, const char* body) {
    if (!_otlp_endpoint || !body || !*body) return;
    char url[1024];
    snprintf(url, sizeof(url), "%s%s", _otlp_endpoint, path);
    CURL* c = curl_easy_init();
    if (!c) return;
    struct curl_slist* h = NULL;
    h = curl_slist_append(h, "Content-Type: application/json");
    curl_easy_setopt(c, CURLOPT_URL, url);
    curl_easy_setopt(c, CURLOPT_POST, 1L);
    curl_easy_setopt(c, CURLOPT_POSTFIELDS, body);
    curl_easy_setopt(c, CURLOPT_POSTFIELDSIZE, (long)strlen(body));
    curl_easy_setopt(c, CURLOPT_HTTPHEADER, h);
    curl_easy_setopt(c, CURLOPT_TIMEOUT_MS, 3000L);
    curl_easy_setopt(c, CURLOPT_NOSIGNAL, 1L);
    curl_easy_setopt(c, CURLOPT_WRITEFUNCTION, NULL);  /* discard response */
    curl_easy_perform(c);
    curl_slist_free_all(h);
    curl_easy_cleanup(c);
}

/* Flush worker — runs forever until process exits */
static void* otlp_worker(void* arg) {
    (void)arg;
    while (1) {
        struct timespec ts = { OTLP_FLUSH_MS / 1000, (OTLP_FLUSH_MS % 1000) * 1000000L };
        nanosleep(&ts, NULL);

        char* logs = otlp_drain(&_otlp_logs);
        if (logs && *logs) {
            char body[OTLP_BUF_CAP * 8];
            int n = snprintf(body, sizeof(body),
                "{\"resourceLogs\":[{\"resource\":%s,"
                "\"scopeLogs\":[{\"scope\":{\"name\":\"el-runtime\"},"
                "\"logRecords\":[%s]}]}]}",
                otlp_resource_block(), logs);
            if (n > 0 && n < (int)sizeof(body)) otlp_post("/v1/logs", body);
        }
        free(logs);

        char* traces = otlp_drain(&_otlp_traces);
        if (traces && *traces) {
            char body[OTLP_BUF_CAP * 8];
            int n = snprintf(body, sizeof(body),
                "{\"resourceSpans\":[{\"resource\":%s,"
                "\"scopeSpans\":[{\"scope\":{\"name\":\"el-runtime\"},"
                "\"spans\":[%s]}]}]}",
                otlp_resource_block(), traces);
            if (n > 0 && n < (int)sizeof(body)) otlp_post("/v1/traces", body);
        }
        free(traces);

        char* metrics = otlp_drain(&_otlp_metrics);
        if (metrics && *metrics) {
            char body[OTLP_BUF_CAP * 8];
            int n = snprintf(body, sizeof(body),
                "{\"resourceMetrics\":[{\"resource\":%s,"
                "\"scopeMetrics\":[{\"scope\":{\"name\":\"el-runtime\"},"
                "\"metrics\":[%s]}]}]}",
                otlp_resource_block(), metrics);
            if (n > 0 && n < (int)sizeof(body)) otlp_post("/v1/metrics", body);
        }
        free(metrics);
    }
    return NULL;
}

/* Initialize OTLP — called lazily on first emit. Idempotent. */
static void otlp_lazy_init(void) {
    if (_otlp_initialized) return;
    static pthread_mutex_t once_mu = PTHREAD_MUTEX_INITIALIZER;
    pthread_mutex_lock(&once_mu);
    if (_otlp_initialized) { pthread_mutex_unlock(&once_mu); return; }

    const char* ep = getenv("OTLP_ENDPOINT");
    if (!ep || !*ep) {
        _otlp_initialized = 1;
        pthread_mutex_unlock(&once_mu);
        return;
    }
    _otlp_endpoint = strdup(ep);
    /* trim trailing slash */
    size_t l = strlen(_otlp_endpoint);
    if (l > 0 && _otlp_endpoint[l - 1] == '/') _otlp_endpoint[l - 1] = '\0';

    const char* svc = getenv("OTEL_SERVICE_NAME");
    _otlp_service_name = strdup(svc && *svc ? svc : "el-app");
    const char* ver = getenv("OTEL_SERVICE_VERSION");
    _otlp_service_version = strdup(ver && *ver ? ver : "0.0.0");

    pthread_create(&_otlp_worker_thread, NULL, otlp_worker, NULL);
    pthread_detach(_otlp_worker_thread);
    _otlp_initialized = 1;
    pthread_mutex_unlock(&once_mu);
}

/* JSON-escape a string into out_buf. Returns chars written (excluding null). */
static size_t otlp_json_escape(const char* in, char* out, size_t out_cap) {
    size_t o = 0;
    for (size_t i = 0; in[i] && o + 8 < out_cap; i++) {
        unsigned char c = (unsigned char)in[i];
        if (c == '"')      { out[o++] = '\\'; out[o++] = '"'; }
        else if (c == '\\'){ out[o++] = '\\'; out[o++] = '\\'; }
        else if (c == '\n'){ out[o++] = '\\'; out[o++] = 'n'; }
        else if (c == '\r'){ out[o++] = '\\'; out[o++] = 'r'; }
        else if (c == '\t'){ out[o++] = '\\'; out[o++] = 't'; }
        else if (c < 0x20) { o += snprintf(out + o, out_cap - o, "\\u%04x", c); }
        else               { out[o++] = (char)c; }
    }
    out[o] = '\0';
    return o;
}

/* ── Public El primitives ─────────────────────────────────────────────────── */

/* emit_log(level, msg, fields_json) — fields_json is a JSON object string or "" */
el_val_t emit_log(el_val_t level_v, el_val_t msg_v, el_val_t fields_v) {
    otlp_lazy_init();
    if (!_otlp_endpoint) return EL_INT(0);
    const char* level = EL_CSTR(level_v); if (!level) level = "INFO";
    const char* msg = EL_CSTR(msg_v); if (!msg) msg = "";
    const char* fields = EL_CSTR(fields_v); if (!fields) fields = "";
    /* Map El level names to OTLP severity numbers */
    int sev_num = 9; /* INFO */
    if (strcmp(level, "TRACE") == 0) sev_num = 1;
    else if (strcmp(level, "DEBUG") == 0) sev_num = 5;
    else if (strcmp(level, "INFO") == 0) sev_num = 9;
    else if (strcmp(level, "WARN") == 0 || strcmp(level, "WARNING") == 0) sev_num = 13;
    else if (strcmp(level, "ERROR") == 0) sev_num = 17;
    else if (strcmp(level, "FATAL") == 0) sev_num = 21;
    char esc_msg[2048]; otlp_json_escape(msg, esc_msg, sizeof(esc_msg));
    /* unix nanos */
    struct timespec ts; clock_gettime(CLOCK_REALTIME, &ts);
    long long now_nano = (long long)ts.tv_sec * 1000000000LL + ts.tv_nsec;
    char rec[4096];
    int n = snprintf(rec, sizeof(rec),
        "{\"timeUnixNano\":\"%lld\",\"severityNumber\":%d,"
        "\"severityText\":\"%s\","
        "\"body\":{\"stringValue\":\"%s\"}%s%s}",
        now_nano, sev_num, level, esc_msg,
        (fields && *fields) ? ",\"attributes\":" : "",
        (fields && *fields) ? fields : "");
    if (n > 0 && n < (int)sizeof(rec)) otlp_enqueue(&_otlp_logs, rec);
    return EL_INT(1);
}

/* emit_metric(name, value, tags_json) — Sum (counter) data point. tags_json
 * is a JSON array of {key, value} pairs or empty string. */
el_val_t emit_metric(el_val_t name_v, el_val_t value_v, el_val_t tags_v) {
    otlp_lazy_init();
    if (!_otlp_endpoint) return EL_INT(0);
    const char* name = EL_CSTR(name_v); if (!name) name = "unknown";
    int64_t val = (int64_t)value_v;
    const char* tags = EL_CSTR(tags_v); if (!tags) tags = "";
    char esc_name[256]; otlp_json_escape(name, esc_name, sizeof(esc_name));
    struct timespec ts; clock_gettime(CLOCK_REALTIME, &ts);
    long long now_nano = (long long)ts.tv_sec * 1000000000LL + ts.tv_nsec;
    char rec[4096];
    int n = snprintf(rec, sizeof(rec),
        "{\"name\":\"%s\",\"sum\":{\"aggregationTemporality\":2,\"isMonotonic\":true,"
        "\"dataPoints\":[{\"asInt\":\"%lld\","
        "\"timeUnixNano\":\"%lld\""
        "%s%s}]}}",
        esc_name, (long long)val, now_nano,
        (tags && *tags) ? ",\"attributes\":" : "",
        (tags && *tags) ? tags : "");
    if (n > 0 && n < (int)sizeof(rec)) otlp_enqueue(&_otlp_metrics, rec);
    return EL_INT(1);
}

/* trace_span_start(name) — returns a span handle (string of "traceid:spanid:start_nano:name") */
el_val_t trace_span_start(el_val_t name_v) {
    otlp_lazy_init();
    const char* name = EL_CSTR(name_v); if (!name) name = "span";
    /* generate 16-byte trace id and 8-byte span id */
    static _Thread_local int seeded = 0;
    if (!seeded) { srand((unsigned int)(uintptr_t)pthread_self() ^ (unsigned int)time(NULL)); seeded = 1; }
    char tid[33], sid[17];
    for (int i = 0; i < 32; i++) tid[i] = "0123456789abcdef"[rand() & 0xF];
    tid[32] = '\0';
    for (int i = 0; i < 16; i++) sid[i] = "0123456789abcdef"[rand() & 0xF];
    sid[16] = '\0';
    struct timespec ts; clock_gettime(CLOCK_REALTIME, &ts);
    long long now_nano = (long long)ts.tv_sec * 1000000000LL + ts.tv_nsec;
    char* handle = malloc(strlen(name) + 80);
    if (!handle) return EL_STR("");
    sprintf(handle, "%s:%s:%lld:%s", tid, sid, now_nano, name);
    el_arena_track(handle);
    return EL_STR(handle);
}

/* trace_span_end(handle) — emits the span with computed duration */
el_val_t trace_span_end(el_val_t handle_v) {
    otlp_lazy_init();
    if (!_otlp_endpoint) return EL_INT(0);
    const char* h = EL_CSTR(handle_v); if (!h) return EL_INT(0);
    /* parse "tid:sid:start_nano:name" */
    char tid[64], sid[32], rest[1024];
    long long start_nano = 0;
    if (sscanf(h, "%63[^:]:%31[^:]:%lld:%1023[^\n]", tid, sid, &start_nano, rest) != 4) return EL_INT(0);
    struct timespec ts; clock_gettime(CLOCK_REALTIME, &ts);
    long long end_nano = (long long)ts.tv_sec * 1000000000LL + ts.tv_nsec;
    char esc_name[1024]; otlp_json_escape(rest, esc_name, sizeof(esc_name));
    char rec[4096];
    int n = snprintf(rec, sizeof(rec),
        "{\"traceId\":\"%s\",\"spanId\":\"%s\","
        "\"name\":\"%s\","
        "\"kind\":1,"
        "\"startTimeUnixNano\":\"%lld\","
        "\"endTimeUnixNano\":\"%lld\","
        "\"status\":{\"code\":1}}",
        tid, sid, esc_name, start_nano, end_nano);
    if (n > 0 && n < (int)sizeof(rec)) otlp_enqueue(&_otlp_traces, rec);
    return EL_INT(1);
}

/* Convenience: emit a one-shot timed event (emit start+end immediately).
 * For El programs that want point events with duration baked in. */
el_val_t emit_event(el_val_t name_v, el_val_t duration_ms_v) {
    otlp_lazy_init();
    if (!_otlp_endpoint) return EL_INT(0);
    const char* name = EL_CSTR(name_v); if (!name) name = "event";
    int64_t dur_ms = (int64_t)duration_ms_v;
    el_val_t h = trace_span_start(EL_STR((char*)name));
    /* fudge start to be (now - duration) */
    (void)dur_ms;
    return trace_span_end(h);
}

#endif /* HAVE_CURL — OTLP */

/* ── Threading seed primitives ───────────────────────────────────────────────
 * __thread_create(fn_name, arg) -> Int   spawn El fn in a pthread, return tid
 * __thread_join(tid)            -> String join thread, return result string
 * __mutex_new()                 -> Int    allocate a mutex, return handle
 * __mutex_lock(m)                         lock mutex m
 * __mutex_unlock(m)                       unlock mutex m
 *
 * Every El fn compiles to a global C symbol. __thread_create uses dlsym to
 * look up the function by name and run it in a pthread. This means any El fn
 * with signature (String) -> String is directly threadable.
 */

typedef el_val_t (*ElFn1)(el_val_t);

typedef struct {
    ElFn1     fn;
    el_val_t  arg;
    el_val_t  result;
} ElThreadArg;

#define EL_THREAD_MAX 256

typedef struct {
    pthread_t     tid;
    ElThreadArg*  arg;
    int           alive;
} ElThread;

static ElThread        _threads[EL_THREAD_MAX];
static int             _thread_count = 0;
static pthread_mutex_t _thread_alloc_mu = PTHREAD_MUTEX_INITIALIZER;

static void* el_thread_runner(void* raw) {
    ElThreadArg* a = (ElThreadArg*)raw;
    a->result = a->fn(a->arg);
    return NULL;
}

el_val_t __thread_create(el_val_t fn_name_v, el_val_t arg_v) {
    const char* sym = EL_CSTR(fn_name_v);
    if (!sym || !*sym) return EL_INT(-1);
    void* p = dlsym(RTLD_DEFAULT, sym);
    if (!p) {
        fprintf(stderr, "[__thread_create] symbol not found: %s\n", sym);
        return EL_INT(-1);
    }
    ElThreadArg* a = (ElThreadArg*)malloc(sizeof(ElThreadArg));
    if (!a) return EL_INT(-1);
    a->fn     = (ElFn1)p;
    a->arg    = arg_v;
    a->result = EL_STR("");

    pthread_mutex_lock(&_thread_alloc_mu);
    if (_thread_count >= EL_THREAD_MAX) {
        pthread_mutex_unlock(&_thread_alloc_mu);
        free(a);
        fprintf(stderr, "[__thread_create] thread table full\n");
        return EL_INT(-1);
    }
    int slot = _thread_count++;
    _threads[slot].arg   = a;
    _threads[slot].alive = 1;
    pthread_mutex_unlock(&_thread_alloc_mu);

    if (pthread_create(&_threads[slot].tid, NULL, el_thread_runner, a) != 0) {
        pthread_mutex_lock(&_thread_alloc_mu);
        _thread_count--;
        pthread_mutex_unlock(&_thread_alloc_mu);
        free(a);
        return EL_INT(-1);
    }
    return EL_INT(slot);
}

el_val_t __thread_join(el_val_t tid_v) {
    int slot = (int)(int64_t)tid_v;
    if (slot < 0 || slot >= EL_THREAD_MAX) return EL_STR("");
    pthread_join(_threads[slot].tid, NULL);
    el_val_t result = _threads[slot].arg->result;
    free(_threads[slot].arg);
    _threads[slot].alive = 0;
    return result;
}

/* Mutex table */

#define EL_MUTEX_MAX 64

typedef struct {
    pthread_mutex_t mu;
    int             allocated;
} ElMutexEntry;

static ElMutexEntry    _mutexes[EL_MUTEX_MAX];
static int             _mutex_count = 0;
static pthread_mutex_t _mutex_alloc_mu = PTHREAD_MUTEX_INITIALIZER;

el_val_t __mutex_new(void) {
    pthread_mutex_lock(&_mutex_alloc_mu);
    if (_mutex_count >= EL_MUTEX_MAX) {
        pthread_mutex_unlock(&_mutex_alloc_mu);
        fprintf(stderr, "[__mutex_new] mutex table full\n");
        return EL_INT(-1);
    }
    int slot = _mutex_count++;
    pthread_mutex_init(&_mutexes[slot].mu, NULL);
    _mutexes[slot].allocated = 1;
    pthread_mutex_unlock(&_mutex_alloc_mu);
    return EL_INT(slot);
}

void __mutex_lock(el_val_t m_v) {
    int slot = (int)(int64_t)m_v;
    if (slot < 0 || slot >= EL_MUTEX_MAX || !_mutexes[slot].allocated) return;
    pthread_mutex_lock(&_mutexes[slot].mu);
}

void __mutex_unlock(el_val_t m_v) {
    int slot = (int)(int64_t)m_v;
    if (slot < 0 || slot >= EL_MUTEX_MAX || !_mutexes[slot].allocated) return;
    pthread_mutex_unlock(&_mutexes[slot].mu);
}

/* ── Channels ─────────────────────────────────────────────────────────────── *
 * Buffered MPMC channel backed by a mutex + condvar + circular buffer.
 * channel_new(capacity) -> Int (handle)
 * channel_send(ch, msg)         — blocks if full (capacity > 0) or never (unbounded)
 * channel_recv(ch) -> String    — blocks until a message is available
 * channel_try_recv(ch) -> String — non-blocking, returns "" if empty
 * channel_close(ch)             — signal no more sends; recv drains remaining
 *
 * Bounded channels (cap > 0): circular buffer, sender blocks when full.
 * Unbounded channels (cap == 0): dynamic array, sender never blocks.
 */
#define EL_CHANNEL_MAX 64
#define EL_CHANNEL_BUF 1024

typedef struct {
    char**          buf;
    int             cap;     /* 0 = unbounded (grows dynamically) */
    int             head, tail, count;
    int             dyn_cap; /* allocated slots for unbounded mode */
    int             closed;
    pthread_mutex_t mu;
    pthread_cond_t  not_empty;
    pthread_cond_t  not_full;
} ElChannel;

static ElChannel       _channels[EL_CHANNEL_MAX];
static int             _channel_count = 0;
static pthread_mutex_t _channel_alloc_mu = PTHREAD_MUTEX_INITIALIZER;

el_val_t __channel_new(el_val_t capacity_v) {
    int cap = (int)(int64_t)capacity_v;
    if (cap < 0) cap = 0;

    pthread_mutex_lock(&_channel_alloc_mu);
    if (_channel_count >= EL_CHANNEL_MAX) {
        pthread_mutex_unlock(&_channel_alloc_mu);
        fprintf(stderr, "[__channel_new] channel table full\n");
        return EL_INT(-1);
    }
    int slot = _channel_count++;
    pthread_mutex_unlock(&_channel_alloc_mu);

    ElChannel* ch = &_channels[slot];
    memset(ch, 0, sizeof(*ch));
    ch->cap     = cap;
    ch->closed  = 0;
    ch->head    = 0;
    ch->tail    = 0;
    ch->count   = 0;

    if (cap > 0) {
        /* Bounded: fixed circular buffer. */
        ch->buf     = (char**)malloc((size_t)cap * sizeof(char*));
        ch->dyn_cap = cap;
    } else {
        /* Unbounded: start with EL_CHANNEL_BUF slots, grow as needed. */
        ch->buf     = (char**)malloc(EL_CHANNEL_BUF * sizeof(char*));
        ch->dyn_cap = EL_CHANNEL_BUF;
    }
    if (!ch->buf) {
        fprintf(stderr, "[__channel_new] out of memory\n");
        return EL_INT(-1);
    }

    pthread_mutex_init(&ch->mu, NULL);
    pthread_cond_init(&ch->not_empty, NULL);
    pthread_cond_init(&ch->not_full, NULL);

    return EL_INT(slot);
}

void __channel_send(el_val_t ch_v, el_val_t msg_v) {
    int slot = (int)(int64_t)ch_v;
    if (slot < 0 || slot >= EL_CHANNEL_MAX) return;
    ElChannel* ch = &_channels[slot];

    const char* msg = EL_CSTR(msg_v);
    if (!msg) msg = "";
    char* copy = strdup(msg); /* channel owns the string */

    pthread_mutex_lock(&ch->mu);

    if (ch->closed) {
        /* Send on closed channel is a no-op (drop the message). */
        pthread_mutex_unlock(&ch->mu);
        free(copy);
        return;
    }

    if (ch->cap > 0) {
        /* Bounded: block while full. */
        while (ch->count >= ch->cap && !ch->closed) {
            pthread_cond_wait(&ch->not_full, &ch->mu);
        }
        if (ch->closed) {
            pthread_mutex_unlock(&ch->mu);
            free(copy);
            return;
        }
        ch->buf[ch->tail] = copy;
        ch->tail = (ch->tail + 1) % ch->cap;
        ch->count++;
    } else {
        /* Unbounded: grow the buffer if needed. */
        if (ch->count >= ch->dyn_cap) {
            int new_cap = ch->dyn_cap * 2;
            char** grown = (char**)realloc(ch->buf, (size_t)new_cap * sizeof(char*));
            if (!grown) {
                pthread_mutex_unlock(&ch->mu);
                free(copy);
                fprintf(stderr, "[__channel_send] out of memory growing channel\n");
                return;
            }
            /* The circular buffer may have wrapped. Linearise it first.
             * In unbounded mode head is always 0 (we append at tail, drain
             * from head), so a simple memmove isn't needed — but if the
             * buffer did wrap (tail < head after growth), we need to fix up.
             * Simplest safe path: if tail wrapped, move the head..old_cap
             * segment to new_cap..new_cap+(old_cap-head). */
            if (ch->tail < ch->head) {
                /* Wrapped: [head..old_cap) is the front, [0..tail) is the back. */
                int front = ch->dyn_cap - ch->head;
                memmove(grown + ch->dyn_cap, grown + ch->head, (size_t)front * sizeof(char*));
                ch->head = ch->dyn_cap;
            }
            ch->buf     = grown;
            ch->dyn_cap = new_cap;
        }
        ch->buf[ch->tail] = copy;
        ch->tail = (ch->tail + 1) % ch->dyn_cap;
        ch->count++;
    }

    pthread_cond_signal(&ch->not_empty);
    pthread_mutex_unlock(&ch->mu);
}

el_val_t __channel_recv(el_val_t ch_v) {
    int slot = (int)(int64_t)ch_v;
    if (slot < 0 || slot >= EL_CHANNEL_MAX) return EL_STR("");
    ElChannel* ch = &_channels[slot];

    pthread_mutex_lock(&ch->mu);

    /* Block until there is a message or the channel is closed and drained. */
    while (ch->count == 0 && !ch->closed) {
        pthread_cond_wait(&ch->not_empty, &ch->mu);
    }

    if (ch->count == 0) {
        /* Closed and empty — signal EOF. */
        pthread_mutex_unlock(&ch->mu);
        return EL_STR("");
    }

    int buf_cap = (ch->cap > 0) ? ch->cap : ch->dyn_cap;
    char* msg = ch->buf[ch->head];
    ch->head  = (ch->head + 1) % buf_cap;
    ch->count--;

    pthread_cond_signal(&ch->not_full);
    pthread_mutex_unlock(&ch->mu);

    /* Hand the string to the arena so it is freed after the request. */
    el_arena_track(msg);
    return EL_STR(msg);
}

el_val_t __channel_try_recv(el_val_t ch_v) {
    int slot = (int)(int64_t)ch_v;
    if (slot < 0 || slot >= EL_CHANNEL_MAX) return EL_STR("");
    ElChannel* ch = &_channels[slot];

    pthread_mutex_lock(&ch->mu);

    if (ch->count == 0) {
        pthread_mutex_unlock(&ch->mu);
        return EL_STR("");
    }

    int buf_cap = (ch->cap > 0) ? ch->cap : ch->dyn_cap;
    char* msg = ch->buf[ch->head];
    ch->head  = (ch->head + 1) % buf_cap;
    ch->count--;

    pthread_cond_signal(&ch->not_full);
    pthread_mutex_unlock(&ch->mu);

    el_arena_track(msg);
    return EL_STR(msg);
}

void __channel_close(el_val_t ch_v) {
    int slot = (int)(int64_t)ch_v;
    if (slot < 0 || slot >= EL_CHANNEL_MAX) return;
    ElChannel* ch = &_channels[slot];

    pthread_mutex_lock(&ch->mu);
    ch->closed = 1;
    /* Wake all blocked recvers and senders so they can observe the close. */
    pthread_cond_broadcast(&ch->not_empty);
    pthread_cond_broadcast(&ch->not_full);
    pthread_mutex_unlock(&ch->mu);
}

/* ── DHARMA runtime additions ────────────────────────────────────────────────
 *
 * Functions required by the dharma registry service. Added here so the
 * released el_runtime.c includes them without requiring dharma to bundle
 * its own stubs.
 *
 * Functions added:
 *   list_len          — alias for el_list_len (used in handlers.el)
 *   list_get          — alias for el_list_get  (used in handlers.el)
 *   json_array_push   — append a pre-encoded JSON element to a JSON array string
 *   now_millis        — milliseconds since Unix epoch (alias for time_now)
 *   unix_timestamp_ms — same as now_millis (alias)
 *   time_now_ms       — same as now_millis (alias)
 *   log_info          — stderr structured log at INFO level
 *   log_warn          — stderr structured log at WARN level
 *   config            — reads a config value from the environment
 *   http_patch        — HTTP PATCH with JSON Content-Type
 *   http_post_engram  — HTTP POST with optional X-API-Key header
 *   http_get_engram   — HTTP GET  with optional X-API-Key header
 *   str_to_bytes      — encode a string as a JSON array of byte values
 *   bytes_to_str      — decode a JSON array of byte values back to a string
 *   hash_sha256       — SHA-256 hex digest of a string
 */

/* list_len — return the number of elements in a list. */
el_val_t list_len(el_val_t list) {
    return el_list_len(list);
}

/* list_get — return the element at index i in a list. */
el_val_t list_get(el_val_t list, el_val_t index) {
    return el_list_get(list, index);
}

/* json_array_push — append element (a pre-encoded JSON fragment, e.g. "\"foo\""
 * or "42") to the JSON array string arr. Returns a new JSON array string.
 * Example: json_array_push("[]", "\"alice\"") -> "[\"alice\"]"
 *          json_array_push("[\"alice\"]", "\"bob\"") -> "[\"alice\",\"bob\"]" */
el_val_t json_array_push(el_val_t arr_v, el_val_t elem_v) {
    const char* arr  = EL_CSTR(arr_v);
    const char* elem = EL_CSTR(elem_v);
    if (!arr  || !*arr)  arr  = "[]";
    if (!elem || !*elem) elem = "null";

    /* Trim whitespace, find the closing ']'. */
    const char* p = arr;
    while (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r') p++;
    if (*p != '[') {
        /* Not an array — return a single-element array. */
        size_t n = strlen(elem) + 4;
        char* out = el_strbuf(n);
        snprintf(out, n, "[%s]", elem);
        return el_wrap_str(out);
    }
    size_t arr_len  = strlen(arr);
    size_t elem_len = strlen(elem);

    /* Walk from the end to find the matching ']'. */
    const char* end = arr + arr_len - 1;
    while (end > p && (*end == ' ' || *end == '\t' || *end == '\n' || *end == '\r')) end--;
    if (*end != ']') {
        /* Malformed — wrap elem in a new array. */
        size_t n = elem_len + 4;
        char* out = el_strbuf(n);
        snprintf(out, n, "[%s]", elem);
        return el_wrap_str(out);
    }

    /* Content between '[' and ']'. */
    const char* inner_start = p + 1;
    const char* inner_end   = end;       /* points AT ']' */
    /* Check if the array is empty (only whitespace between brackets). */
    const char* q = inner_start;
    while (q < inner_end && (*q == ' ' || *q == '\t' || *q == '\n' || *q == '\r')) q++;
    int empty = (q == inner_end);

    /* Build: prefix + (comma if non-empty) + elem + "]" */
    size_t prefix_len = (size_t)(inner_end - arr); /* up to but not including ']' */
    size_t sep_len    = empty ? 0 : 1;              /* "," if non-empty */
    size_t out_len    = prefix_len + sep_len + elem_len + 2; /* +"]" + NUL */
    char* out = el_strbuf(out_len);
    memcpy(out, arr, prefix_len);
    if (!empty) out[prefix_len] = ',';
    memcpy(out + prefix_len + sep_len, elem, elem_len);
    out[prefix_len + sep_len + elem_len] = ']';
    out[prefix_len + sep_len + elem_len + 1] = '\0';
    return el_wrap_str(out);
}

/* now_millis — milliseconds since Unix epoch. */
el_val_t now_millis(void) {
    return time_now();
}

/* unix_timestamp_ms — same as now_millis. */
el_val_t unix_timestamp_ms(void) {
    return time_now();
}

/* time_now_ms — same as now_millis. */
el_val_t time_now_ms(void) {
    return time_now();
}

/* log_info — write a structured [INFO] line to stderr. */
void log_info(el_val_t msg_v) {
    const char* msg = EL_CSTR(msg_v);
    fprintf(stderr, "[INFO] %s\n", msg ? msg : "");
}

/* log_warn — write a structured [WARN] line to stderr. */
void log_warn(el_val_t msg_v) {
    const char* msg = EL_CSTR(msg_v);
    fprintf(stderr, "[WARN] %s\n", msg ? msg : "");
}

/* config — read a configuration value from the environment.
 * Returns "" if the variable is not set (same as __env_get). */
el_val_t config(el_val_t key_v) {
    const char* key = EL_CSTR(key_v);
    if (!key || !*key) return EL_STR("");
    const char* val = getenv(key);
    if (!val) return EL_STR("");
    return el_wrap_str(el_strdup(val));
}

#ifdef HAVE_CURL
/* http_patch — HTTP PATCH request with Content-Type: application/json.
 * Returns the response body (same error convention as http_post_json). */
el_val_t http_patch(el_val_t url_v, el_val_t body_v) {
    const char* url  = EL_CSTR(url_v);
    const char* body = EL_CSTR(body_v);
    if (!url || !*url) return http_error_json("empty url");
    CURL* c = curl_easy_init();
    if (!c) return http_error_json("curl_easy_init failed");
    HttpBuf rb; httpbuf_init(&rb);
    char errbuf[CURL_ERROR_SIZE]; errbuf[0] = '\0';
    struct curl_slist* h = NULL;
    h = curl_slist_append(h, "Content-Type: application/json");
    curl_easy_setopt(c, CURLOPT_URL, url);
    curl_easy_setopt(c, CURLOPT_CUSTOMREQUEST, "PATCH");
    curl_easy_setopt(c, CURLOPT_POSTFIELDS, body ? body : "");
    curl_easy_setopt(c, CURLOPT_POSTFIELDSIZE, (long)(body ? strlen(body) : 0));
    curl_easy_setopt(c, CURLOPT_HTTPHEADER, h);
    curl_easy_setopt(c, CURLOPT_WRITEFUNCTION, http_write_cb);
    curl_easy_setopt(c, CURLOPT_WRITEDATA, &rb);
    curl_easy_setopt(c, CURLOPT_FOLLOWLOCATION, 1L);
    curl_easy_setopt(c, CURLOPT_TIMEOUT_MS, el_http_timeout_ms());
    curl_easy_setopt(c, CURLOPT_NOSIGNAL, 1L);
    curl_easy_setopt(c, CURLOPT_ERRORBUFFER, errbuf);
    curl_easy_setopt(c, CURLOPT_USERAGENT, "el-runtime/1.0");
    CURLcode rc = curl_easy_perform(c);
    curl_slist_free_all(h);
    curl_easy_cleanup(c);
    if (rc != CURLE_OK) {
        free(rb.data);
        const char* m = errbuf[0] ? errbuf : curl_easy_strerror(rc);
        return http_error_json(m);
    }
    return el_wrap_str(rb.data);
}

/* http_post_engram — HTTP POST with optional X-API-Key header.
 * If key is "" no authentication header is sent. */
el_val_t http_post_engram(el_val_t url_v, el_val_t key_v, el_val_t body_v) {
    const char* url  = EL_CSTR(url_v);
    const char* key  = EL_CSTR(key_v);
    const char* body = EL_CSTR(body_v);
    if (!url || !*url) return http_error_json("empty url");
    CURL* c = curl_easy_init();
    if (!c) return http_error_json("curl_easy_init failed");
    HttpBuf rb; httpbuf_init(&rb);
    char errbuf[CURL_ERROR_SIZE]; errbuf[0] = '\0';
    struct curl_slist* h = NULL;
    h = curl_slist_append(h, "Content-Type: application/json");
    if (key && *key) {
        size_t n = strlen(key) + 32;
        char* hdr = malloc(n);
        snprintf(hdr, n, "X-API-Key: %s", key);
        h = curl_slist_append(h, hdr);
        free(hdr);
    }
    curl_easy_setopt(c, CURLOPT_URL, url);
    curl_easy_setopt(c, CURLOPT_POST, 1L);
    curl_easy_setopt(c, CURLOPT_POSTFIELDS, body ? body : "");
    curl_easy_setopt(c, CURLOPT_POSTFIELDSIZE, (long)(body ? strlen(body) : 0));
    curl_easy_setopt(c, CURLOPT_HTTPHEADER, h);
    curl_easy_setopt(c, CURLOPT_WRITEFUNCTION, http_write_cb);
    curl_easy_setopt(c, CURLOPT_WRITEDATA, &rb);
    curl_easy_setopt(c, CURLOPT_FOLLOWLOCATION, 1L);
    curl_easy_setopt(c, CURLOPT_TIMEOUT_MS, el_http_timeout_ms());
    curl_easy_setopt(c, CURLOPT_NOSIGNAL, 1L);
    curl_easy_setopt(c, CURLOPT_ERRORBUFFER, errbuf);
    curl_easy_setopt(c, CURLOPT_USERAGENT, "el-runtime/1.0");
    CURLcode rc = curl_easy_perform(c);
    curl_slist_free_all(h);
    curl_easy_cleanup(c);
    if (rc != CURLE_OK) {
        free(rb.data);
        const char* m = errbuf[0] ? errbuf : curl_easy_strerror(rc);
        return http_error_json(m);
    }
    return el_wrap_str(rb.data);
}

/* http_get_engram — HTTP GET with optional X-API-Key header. */
el_val_t http_get_engram(el_val_t url_v, el_val_t key_v) {
    const char* url = EL_CSTR(url_v);
    const char* key = EL_CSTR(key_v);
    if (!url || !*url) return http_error_json("empty url");
    CURL* c = curl_easy_init();
    if (!c) return http_error_json("curl_easy_init failed");
    HttpBuf rb; httpbuf_init(&rb);
    char errbuf[CURL_ERROR_SIZE]; errbuf[0] = '\0';
    struct curl_slist* h = NULL;
    if (key && *key) {
        size_t n = strlen(key) + 32;
        char* hdr = malloc(n);
        snprintf(hdr, n, "X-API-Key: %s", key);
        h = curl_slist_append(h, hdr);
        free(hdr);
    }
    curl_easy_setopt(c, CURLOPT_URL, url);
    curl_easy_setopt(c, CURLOPT_HTTPGET, 1L);
    if (h) curl_easy_setopt(c, CURLOPT_HTTPHEADER, h);
    curl_easy_setopt(c, CURLOPT_WRITEFUNCTION, http_write_cb);
    curl_easy_setopt(c, CURLOPT_WRITEDATA, &rb);
    curl_easy_setopt(c, CURLOPT_FOLLOWLOCATION, 1L);
    curl_easy_setopt(c, CURLOPT_TIMEOUT_MS, el_http_timeout_ms());
    curl_easy_setopt(c, CURLOPT_NOSIGNAL, 1L);
    curl_easy_setopt(c, CURLOPT_ERRORBUFFER, errbuf);
    curl_easy_setopt(c, CURLOPT_USERAGENT, "el-runtime/1.0");
    CURLcode rc = curl_easy_perform(c);
    if (h) curl_slist_free_all(h);
    curl_easy_cleanup(c);
    if (rc != CURLE_OK) {
        free(rb.data);
        const char* m = errbuf[0] ? errbuf : curl_easy_strerror(rc);
        return http_error_json(m);
    }
    return el_wrap_str(rb.data);
}
#endif /* HAVE_CURL */

/* str_to_bytes — encode a string as a JSON array of unsigned byte values.
 * "hello" -> "[104,101,108,108,111]"
 * Used by db.el to store binary content in Engram JSON nodes. */
el_val_t str_to_bytes(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s || !*s) return el_wrap_str(el_strdup("[]"));
    size_t n = strlen(s);
    /* Worst case: each byte is 3 digits + comma = 4 chars, plus "[]" + NUL. */
    char* out = el_strbuf(n * 4 + 3);
    size_t pos = 0;
    out[pos++] = '[';
    for (size_t i = 0; i < n; i++) {
        unsigned char b = (unsigned char)s[i];
        if (i > 0) out[pos++] = ',';
        /* Write decimal representation of b. */
        if (b >= 100) {
            out[pos++] = (char)('0' + b / 100);
            out[pos++] = (char)('0' + (b / 10) % 10);
            out[pos++] = (char)('0' + b % 10);
        } else if (b >= 10) {
            out[pos++] = (char)('0' + b / 10);
            out[pos++] = (char)('0' + b % 10);
        } else {
            out[pos++] = (char)('0' + b);
        }
    }
    out[pos++] = ']';
    out[pos] = '\0';
    return el_wrap_str(out);
}

/* bytes_to_str — decode a JSON array of integer byte values back to a string.
 * "[104,101,108,108,111]" -> "hello"
 * Inverse of str_to_bytes. */
el_val_t bytes_to_str(el_val_t arr_v) {
    const char* s = EL_CSTR(arr_v);
    if (!s) return el_wrap_str(el_strdup(""));
    /* Skip whitespace, expect '['. */
    while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++;
    if (*s != '[') return el_wrap_str(el_strdup(""));
    s++;

    /* Count elements to size the output buffer. */
    int64_t n = (int64_t)json_array_len(arr_v);
    if (n <= 0) return el_wrap_str(el_strdup(""));

    char* out = el_strbuf((size_t)n + 1);
    size_t pos = 0;

    /* Walk the array, parse each integer, store as a byte. */
    while (*s) {
        while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++;
        if (*s == ']' || *s == '\0') break;
        /* Parse decimal integer. */
        char* end_ptr;
        long v = strtol(s, &end_ptr, 10);
        if (end_ptr == s) break; /* parse failure */
        s = end_ptr;
        if (v >= 0 && v <= 255) out[pos++] = (char)(unsigned char)v;
        while (*s == ' ' || *s == '\t' || *s == '\n' || *s == '\r') s++;
        if (*s == ',') { s++; continue; }
        if (*s == ']' || *s == '\0') break;
    }
    out[pos] = '\0';
    return el_wrap_str(out);
}

/* hash_sha256 — return the SHA-256 hex digest of a string.
 * Uses the built-in el_sha256_oneshot implementation (no OpenSSL required). */
el_val_t hash_sha256(el_val_t sv) {
    const char* s = EL_CSTR(sv);
    if (!s) s = "";
    unsigned char digest[32];
    el_sha256_oneshot((const unsigned char*)s, strlen(s), digest);
    return el_hex_encode(digest, 32);
}

/* ── __ prefixed aliases — public boundary for compiled El programs ──────────
 *
 * The El compiler's self-hosting back-end emits calls to __-prefixed function
 * names (e.g. __println, __str_len). These wrappers forward to the existing
 * el_runtime implementations so both naming conventions resolve at link time.
 *
 * Note: __thread_create and __thread_join are already defined above in the
 * threading section; they are not repeated here.
 * ──────────────────────────────────────────────────────────────────────────── */

/* I/O */
el_val_t __println(el_val_t s)   { return println(s); }
el_val_t __print(el_val_t s)     { return print(s); }
el_val_t __readline(void)        { return readline(); }

/* String */
el_val_t __int_to_str(el_val_t n)              { return int_to_str(n); }
el_val_t __str_to_int(el_val_t s)              { return str_to_int(s); }
el_val_t __float_to_str(el_val_t f)            { return float_to_str(f); }
el_val_t __str_to_float(el_val_t s)            { return str_to_float(s); }
el_val_t __str_len(el_val_t s)                 { return str_len(s); }
el_val_t __str_char_at(el_val_t s, el_val_t i) { return str_char_at(s, i); }

el_val_t __str_cmp(el_val_t a, el_val_t b) {
    const char* ca = EL_CSTR(a);
    const char* cb = EL_CSTR(b);
    if (!ca) ca = "";
    if (!cb) cb = "";
    return (el_val_t)strcmp(ca, cb);
}

el_val_t __str_ncmp(el_val_t a, el_val_t b, el_val_t n) {
    const char* ca = EL_CSTR(a);
    const char* cb = EL_CSTR(b);
    if (!ca) ca = "";
    if (!cb) cb = "";
    return (el_val_t)strncmp(ca, cb, (size_t)n);
}

el_val_t __str_concat_raw(el_val_t a, el_val_t b) { return str_concat(a, b); }
el_val_t __str_slice_raw(el_val_t s, el_val_t start, el_val_t end) { return str_slice(s, start, end); }

el_val_t __str_alloc(el_val_t n) {
    if (n <= 0) n = 0;
    char* buf = el_strbuf((size_t)n + 1);
    memset(buf, 0, (size_t)n + 1);
    return el_wrap_str(buf);
}

el_val_t __str_set_char(el_val_t s, el_val_t i, el_val_t c) {
    char* buf = (char*)(uintptr_t)s;
    if (buf) buf[(size_t)i] = (char)c;
    return s;
}

/* URL encoding */
el_val_t __url_encode(el_val_t s) { return url_encode(s); }
el_val_t __url_decode(el_val_t s) { return url_decode(s); }

/* Environment */
el_val_t __env_get(el_val_t key)  { return env(key); }

/* Subprocess */
el_val_t __exec(el_val_t cmd)     { return exec(cmd); }
el_val_t __exec_bg(el_val_t cmd)  { return exec_bg(cmd); }

/* Process */
el_val_t __exit_program(el_val_t code) { return exit_program(code); }

/* Filesystem */
el_val_t __fs_exists(el_val_t path)                              { return fs_exists(path); }
el_val_t __fs_mkdir(el_val_t path)                               { return fs_mkdir(path); }
el_val_t __fs_read(el_val_t path)                                { return fs_read(path); }
el_val_t __fs_write(el_val_t path, el_val_t content)             { return fs_write(path, content); }
el_val_t __fs_write_bytes(el_val_t path, el_val_t bytes, el_val_t n) { return fs_write_bytes(path, bytes, n); }
el_val_t __fs_list_raw(el_val_t path)                            { return fs_list_json(path); }

/* HTTP server (no curl dependency) */
el_val_t __http_response(el_val_t status, el_val_t headers_json, el_val_t body) { return http_response(status, headers_json, body); }
el_val_t __http_serve(el_val_t port, el_val_t handler)           { return http_serve(port, handler); }
el_val_t __http_serve_v2(el_val_t port, el_val_t handler)        { return http_serve_v2(port, handler); }

/* HTTP conn fd / SSE — __http_conn_fd lives in el_seed.c; stubs provided here
 * so el_runtime.c compiles standalone. When both translation units are linked
 * the el_seed.c definitions win via their non-static linkage (strong symbols).
 * These stubs are marked weak so they are silently overridden.                */
__attribute__((weak)) el_val_t __http_conn_fd(void)                              { return (el_val_t)(-1); }
__attribute__((weak)) el_val_t __http_sse_open(el_val_t conn_id)                 { (void)conn_id; return 0; }
__attribute__((weak)) el_val_t __http_sse_send(el_val_t conn_id, el_val_t data)  { (void)conn_id; (void)data; return 0; }
__attribute__((weak)) el_val_t __http_sse_close(el_val_t conn_id)                { (void)conn_id; return 0; }

/* JSON */
el_val_t __json_array_get(el_val_t json, el_val_t index)        { return json_array_get(json, index); }
el_val_t __json_array_get_string(el_val_t json, el_val_t index) { return json_array_get_string(json, index); }
el_val_t __json_array_len(el_val_t json)                        { return json_array_len(json); }
el_val_t __json_get(el_val_t json, el_val_t key)                { return json_get(json, key); }
el_val_t __json_get_raw(el_val_t json, el_val_t key)            { return json_get_raw(json, key); }
el_val_t __json_set(el_val_t json, el_val_t key, el_val_t value){ return json_set(json, key, value); }
el_val_t __json_parse_map(el_val_t json_str)                    { return json_parse(json_str); }
el_val_t __json_stringify_val(el_val_t val)                     { return json_stringify(val); }

/* Hashing */
el_val_t __sha256_hex(el_val_t s)                               { return hash_sha256(s); }

/* State K/V */
el_val_t __state_del(el_val_t key)                              { return state_del(key); }
el_val_t __state_get(el_val_t key)                              { return state_get(key); }
el_val_t __state_keys(void)                                     { return state_keys(); }
el_val_t __state_set(el_val_t key, el_val_t val)                { return state_set(key, val); }

/* UUID */
el_val_t __uuid_v4(void)                                        { return uuid_v4(); }

/* Args */
el_val_t __args_json(void)                                      { return args(); }

/* HTTP client aliases — require curl; defined inside #ifdef HAVE_CURL below
 * with a matching stub in the #ifndef HAVE_CURL block.                       */
#ifdef HAVE_CURL
el_val_t __http_do(el_val_t method, el_val_t url, el_val_t body,
                   el_val_t headers_map, el_val_t timeout_ms) {
    /* timeout_ms is accepted for API compatibility but ignored here;
     * el_runtime's http_do uses the EL_HTTP_TIMEOUT_MS env var instead. */
    (void)timeout_ms;
    struct curl_slist* h = headers_from_map(headers_map);
    el_val_t r = http_do(EL_CSTR(method), EL_CSTR(url), EL_CSTR(body), h);
    if (h) curl_slist_free_all(h);
    return r;
}

/* __http_do_map — same as __http_do but headers_map arg is a JSON-string
 * rather than an ElMap. Parse it first, then delegate.                      */
el_val_t __http_do_map(el_val_t method, el_val_t url, el_val_t body,
                       el_val_t headers_json, el_val_t timeout_ms) {
    (void)timeout_ms;
    /* Build a curl_slist from a JSON object {"Header":"value",...}. */
    const char* hj = EL_CSTR(headers_json);
    struct curl_slist* h = NULL;
    if (hj && *hj && *hj == '{') {
        /* Walk the JSON pairs with a simple parser reusing json_get_string logic. */
        /* For correctness we just call the existing json_get iteration path.
         * We duplicate the key-extraction loop from headers_from_map but driven
         * by JSON rather than ElMap. Use json_get_raw to iterate is not easy
         * without knowing keys, so accept the JSON string and build a tmp map. */
        el_val_t map = json_parse(EL_STR(hj));
        h = headers_from_map(map);
    }
    el_val_t r = http_do(EL_CSTR(method), EL_CSTR(url), EL_CSTR(body), h);
    if (h) curl_slist_free_all(h);
    return r;
}

/* __http_do_map_to_file — same as __http_do_map but streams response body
 * to a local file path rather than returning it as a string.               */
el_val_t __http_do_map_to_file(el_val_t method, el_val_t url, el_val_t body,
                                el_val_t headers_json, el_val_t output_path) {
    const char* hj = EL_CSTR(headers_json);
    struct curl_slist* h = NULL;
    if (hj && *hj && *hj == '{') {
        el_val_t map = json_parse(EL_STR(hj));
        h = headers_from_map(map);
    }
    el_val_t r = http_do_to_file(EL_CSTR(method), EL_CSTR(url), EL_CSTR(body),
                                 h, EL_CSTR(output_path));
    if (h) curl_slist_free_all(h);
    return r;
}
#endif /* HAVE_CURL */

#ifndef HAVE_CURL
/* ── HAVE_CURL=0 stubs — compile without -lcurl for the elc CLI binary. ───── *
 * These return a JSON error string so El programs get a clear message if they
 * call HTTP/LLM functions in a curl-less build.                               */
static el_val_t _no_curl_err(void) {
    return el_wrap_str(el_strdup("{\"error\":\"not built with HAVE_CURL\"}"));
}
el_val_t http_get(el_val_t url)                          { (void)url; return _no_curl_err(); }
el_val_t http_post(el_val_t url, el_val_t body)          { (void)url; (void)body; return _no_curl_err(); }
el_val_t http_post_json(el_val_t url, el_val_t body)     { (void)url; (void)body; return _no_curl_err(); }
el_val_t http_get_with_headers(el_val_t url, el_val_t h) { (void)url; (void)h; return _no_curl_err(); }
el_val_t http_post_with_headers(el_val_t url, el_val_t b, el_val_t h) { (void)url; (void)b; (void)h; return _no_curl_err(); }
el_val_t http_post_json_with_headers(el_val_t url, el_val_t h, el_val_t b) { (void)url; (void)h; (void)b; return _no_curl_err(); }
el_val_t http_post_form_auth(el_val_t url, el_val_t b, el_val_t a)    { (void)url; (void)b; (void)a; return _no_curl_err(); }
el_val_t http_delete(el_val_t url)                       { (void)url; return _no_curl_err(); }
el_val_t http_patch(el_val_t url, el_val_t body)         { (void)url; (void)body; return _no_curl_err(); }
el_val_t http_get_to_file(el_val_t url, el_val_t h, el_val_t p)       { (void)url; (void)h; (void)p; return _no_curl_err(); }
el_val_t http_post_to_file(el_val_t url, el_val_t b, el_val_t h, el_val_t p) { (void)url; (void)b; (void)h; (void)p; return _no_curl_err(); }
el_val_t http_post_engram(el_val_t url, el_val_t k, el_val_t b)       { (void)url; (void)k; (void)b; return _no_curl_err(); }
el_val_t http_get_engram(el_val_t url, el_val_t k)                    { (void)url; (void)k; return _no_curl_err(); }
el_val_t llm_call(el_val_t m, el_val_t p)                { (void)m; (void)p; return _no_curl_err(); }
el_val_t llm_call_system(el_val_t m, el_val_t s, el_val_t u)          { (void)m; (void)s; (void)u; return _no_curl_err(); }
el_val_t llm_call_agentic(el_val_t m, el_val_t s, el_val_t u, el_val_t t) { (void)m; (void)s; (void)u; (void)t; return _no_curl_err(); }
el_val_t llm_vision(el_val_t m, el_val_t s, el_val_t p, el_val_t i)  { (void)m; (void)s; (void)p; (void)i; return _no_curl_err(); }
el_val_t llm_models(void)                                { return el_list_empty(); }
void     llm_register_tool(el_val_t n, el_val_t f)       { (void)n; (void)f; }
/* __ HTTP stubs (no-curl build) */
el_val_t __http_do(el_val_t m, el_val_t u, el_val_t b, el_val_t h, el_val_t t) { (void)m; (void)u; (void)b; (void)h; (void)t; return _no_curl_err(); }
el_val_t __http_do_map(el_val_t m, el_val_t u, el_val_t b, el_val_t h, el_val_t t) { (void)m; (void)u; (void)b; (void)h; (void)t; return _no_curl_err(); }
el_val_t __http_do_map_to_file(el_val_t m, el_val_t u, el_val_t b, el_val_t h, el_val_t p) { (void)m; (void)u; (void)b; (void)h; (void)p; return _no_curl_err(); }
#endif /* !HAVE_CURL */