/* test_bufpool.c — M4 gate for the demand-paging BUFFER POOL (engram_store.{c,h}).
 *
 * Pure C. Build: gcc -O2 test_bufpool.c ../../lang/runtime/engram_store.c -o t
 * Writes ONLY under a throwaway /tmp dir. Never touches ~/.neuron or live ports.
 *
 * Proves the M4 pool preserves every M1/M2 invariant when the pool is SMALLER
 * than the store (pages evict + re-fault): small-pool round-trip correctness,
 * LRU eviction policy (hot resident / cold evicted / no dirty stolen), pinned
 * residency (superblocks, index roots, explicit page + hot-layer pins), bounded
 * read-ahead, and crash safety (WAL replay + checkpoint-crash) under paging.
 */
#include "../../lang/runtime/engram_store.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>

static int g_pass = 0, g_fail = 0;
static void ok(const char* name, int cond){
    printf("  [%s] %s\n", cond ? "PASS" : "FAIL", name);
    if (cond) g_pass++; else g_fail++;
}

static char g_dir[512];
static void mk_dir(void){
    snprintf(g_dir, sizeof g_dir, "/tmp/engram-bufpool-test-%d", (int)getpid());
    mkdir(g_dir, 0700);
}
static void path_in(char* out, size_t cap, const char* name){
    snprintf(out, cap, "%s/%s", g_dir, name);
}

/* ── deterministic generators (bit-exact regeneration for oracles) ─────────── */
static uint64_t xs(uint64_t* s){ uint64_t x=*s; x^=x<<13; x^=x>>7; x^=x<<17; *s=x; return x; }
static uint64_t node_seed(int i){ return 0x9E3779B97F4A7C15ULL ^ ((uint64_t)(i+1)*0xD1B54A32D192ED03ULL); }
static uint64_t edge_seed(int i){ return 0xC2B2AE3D27D4EB4FULL ^ ((uint64_t)(i+1)*0x165667B19E3779F9ULL); }
static char* rnd_str(uint64_t* st, size_t len){
    char* s = (char*)malloc(len + 1);
    for (size_t i=0;i<len;i++) s[i] = (char)(33 + (xs(st) % 94));
    s[len] = 0; return s;
}

#define NODE_COUNT 5000
#define EDGE_COUNT 20000
#define EMB_DIM    768
#define CK_NODES   300

static void noop_node_cb(const StoreNode* n, void* ctx){ (void)n; (void)ctx; }

static void gen_node(int i, StoreNode* n){
    memset(n, 0, sizeof *n);
    uint64_t st = node_seed(i);
    char id[32]; snprintf(id, sizeof id, "node-%d", i);
    n->id = strdup(id);
    size_t clen = (i % 500 == 0) ? (size_t)(17000 + (xs(&st) % 6000)) : (size_t)(xs(&st) % 300);
    n->content   = rnd_str(&st, clen);
    n->node_type = rnd_str(&st, 4 + (xs(&st) % 8));
    n->label     = (i % 2)   ? rnd_str(&st, 3 + (xs(&st) % 10)) : NULL;
    n->tier      = rnd_str(&st, 4 + (xs(&st) % 6));
    n->tags      = rnd_str(&st, xs(&st) % 40);
    n->metadata  = (i % 3)   ? rnd_str(&st, xs(&st) % 60) : NULL;
    n->salience             = (double)(xs(&st) % 1000000) / 997.0;
    n->importance           = (double)(xs(&st) % 1000000) / 131.0;
    n->confidence           = (double)(xs(&st) % 1000000) / 733.0;
    n->temporal_decay_rate  = (double)(xs(&st) % 1000000) / 101.0;
    n->activation_count     = (int64_t)(xs(&st) % 100000);
    n->last_activated       = (int64_t)xs(&st);
    n->created_at           = (int64_t)(1600000000000LL + i);
    n->updated_at           = (int64_t)xs(&st);
    n->background_activation = (double)(xs(&st) % 1000000) / 17.0;
    n->working_memory_weight = (double)(xs(&st) % 1000000) / 29.0;
    n->suppression_count    = (int32_t)(xs(&st) % 50);
    n->layer_id             = (uint32_t)(xs(&st) % 5);
    for (int k=0;k<STORE_BLL_K;k++) n->access_ts[k] = (int64_t)xs(&st);
    n->access_head   = (int32_t)(xs(&st) % STORE_BLL_K);
    n->access_filled = (int32_t)(xs(&st) % (STORE_BLL_K + 1));
    n->wm_anchor     = (double)(xs(&st) % 1000000) / 3.0;
    n->emb = (float*)malloc(EMB_DIM * sizeof(float));
    for (int k=0;k<EMB_DIM;k++){ uint32_t u=(uint32_t)xs(&st); memcpy(&n->emb[k], &u, 4); }
    n->emb_dim = EMB_DIM;
}
static void gen_edge(int i, StoreEdge* e){
    memset(e, 0, sizeof *e);
    uint64_t st = edge_seed(i);
    char id[32], from[32], to[32];
    snprintf(id, sizeof id, "edge-%d", i);
    snprintf(from, sizeof from, "node-%d", (int)(xs(&st) % NODE_COUNT));
    snprintf(to,   sizeof to,   "node-%d", (int)(xs(&st) % NODE_COUNT));
    e->id = strdup(id); e->from_id = strdup(from); e->to_id = strdup(to);
    e->relation = rnd_str(&st, 3 + (xs(&st) % 12));
    e->metadata = (i % 4) ? rnd_str(&st, xs(&st) % 40) : NULL;
    e->weight     = (double)(xs(&st) % 1000000) / 111.0;
    e->hebb       = (double)(xs(&st) % 1000000) / 1000000.0;
    e->confidence = (double)(xs(&st) % 1000000) / 777.0;
    e->created_at = (int64_t)(1600000000000LL + i);
    e->updated_at = (int64_t)xs(&st);
    e->last_fired = (int64_t)xs(&st);
    e->inhibitory = (int32_t)(xs(&st) % 2);
    e->layer_id   = (uint32_t)(xs(&st) % 5);
}
static int streq(const char* a, const char* b){
    if (!a && !b) return 1;
    if (!a || !b) return 0;
    return strcmp(a,b)==0;
}
static int cmp_node(const StoreNode* a, const StoreNode* b){
    if (!streq(a->id,b->id) || !streq(a->content,b->content) ||
        !streq(a->node_type,b->node_type) || !streq(a->label,b->label) ||
        !streq(a->tier,b->tier) || !streq(a->tags,b->tags) ||
        !streq(a->metadata,b->metadata)) return 0;
    if (a->salience!=b->salience || a->importance!=b->importance ||
        a->confidence!=b->confidence || a->temporal_decay_rate!=b->temporal_decay_rate ||
        a->activation_count!=b->activation_count || a->last_activated!=b->last_activated ||
        a->created_at!=b->created_at || a->updated_at!=b->updated_at ||
        a->background_activation!=b->background_activation ||
        a->working_memory_weight!=b->working_memory_weight ||
        a->suppression_count!=b->suppression_count || a->layer_id!=b->layer_id ||
        a->access_head!=b->access_head || a->access_filled!=b->access_filled ||
        a->wm_anchor!=b->wm_anchor || a->emb_dim!=b->emb_dim) return 0;
    for (int k=0;k<STORE_BLL_K;k++) if (a->access_ts[k]!=b->access_ts[k]) return 0;
    if ((a->emb==NULL) != (b->emb==NULL)) return 0;
    if (a->emb && memcmp(a->emb, b->emb, (size_t)a->emb_dim*4)!=0) return 0;
    return 1;
}
static int cmp_edge(const StoreEdge* a, const StoreEdge* b){
    if (!streq(a->id,b->id) || !streq(a->from_id,b->from_id) || !streq(a->to_id,b->to_id) ||
        !streq(a->relation,b->relation) || !streq(a->metadata,b->metadata)) return 0;
    if (a->weight!=b->weight || a->hebb!=b->hebb || a->confidence!=b->confidence ||
        a->created_at!=b->created_at || a->updated_at!=b->updated_at ||
        a->last_fired!=b->last_fired || a->inhibitory!=b->inhibitory ||
        a->layer_id!=b->layer_id) return 0;
    return 1;
}
static void free_node_fields(StoreNode* n){
    free(n->id); free(n->content); free(n->node_type); free(n->label);
    free(n->tier); free(n->tags); free(n->metadata); free(n->emb); free(n->unknown);
}
static void free_edge_fields(StoreEdge* e){
    free(e->id); free(e->from_id); free(e->to_id); free(e->relation); free(e->metadata); free(e->unknown);
}

/* ════════════════════════════════════════════════════════════════════════════
 * TEST 1 — SMALL-POOL CORRECTNESS: full M1 workload (5k nodes / 20k edges) with
 * a frame budget FAR smaller than the store → constant eviction + re-fault, yet
 * every read is bit-exact and the pool stays bounded.
 * ════════════════════════════════════════════════════════════════════════════ */
static void test_small_pool_roundtrip(void){
    printf("\n== 1) small-pool correctness: %d nodes + %d edges, cap=%d frames ==\n",
           NODE_COUNT, EDGE_COUNT, 32);
    char path[600]; path_in(path, sizeof path, "small.store");
    unlink(path);
    EngramPagedStore* s = store_create(path);
    ok("store_create", s != NULL);
    if (!s) return;
    store__set_pool_frames(s, 32);          /* pool << store */

    for (int i=0;i<NODE_COUNT;i++){
        StoreNode n; gen_node(i,&n);
        if (store_put_node(s,&n)!=0){ ok("put_node", 0); free_node_fields(&n); store_close(s); return; }
        free_node_fields(&n);
        if ((i%500)==499) store_sync(s);    /* checkpoint: dirty→clean so frames evictable */
    }
    for (int i=0;i<EDGE_COUNT;i++){
        StoreEdge e; gen_edge(i,&e);
        if (store_put_edge(s,&e)!=0){ ok("put_edge", 0); free_edge_fields(&e); store_close(s); return; }
        free_edge_fields(&e);
        if ((i%1000)==999) store_sync(s);
    }
    store_sync(s);

    StorePoolStats st; store_pool_stats(s, &st);
    printf("     pages=%llu  pool: cap=%zu resident=%zu pinned=%zu dirty=%zu evictions=%llu\n",
           (unsigned long long)store_page_count(s), st.cap, st.resident, st.pinned,
           st.dirty, (unsigned long long)st.evictions);
    ok("eviction actually fired (store exceeded the pool)", st.evictions > 0);
    ok("pool stayed bounded (resident <= cap)", st.resident <= st.cap);
    ok("no dirty frames after checkpoint", st.dirty == 0);

    /* read back EVERY node bit-exact despite constant eviction/re-fault */
    int bad = 0;
    for (int i=0;i<NODE_COUNT;i++){
        StoreNode want; gen_node(i,&want);
        StoreNode got; int hit = store_get_node(s, want.id, &got);
        if (hit!=1 || !cmp_node(&want,&got)) bad++;
        if (hit==1) store_node_free(&got);
        free_node_fields(&want);
    }
    ok("all 5000 nodes bit-exact under eviction", bad==0);

    /* sample 4000 edges bit-exact */
    int ebad = 0;
    for (int i=0;i<EDGE_COUNT;i+=5){
        StoreEdge want; gen_edge(i,&want);
        StoreEdge got; int hit = store_get_edge(s, want.id, &got);
        if (hit!=1 || !cmp_edge(&want,&got)) ebad++;
        if (hit==1) store_edge_free(&got);
        free_edge_fields(&want);
    }
    ok("sampled 4000 edges bit-exact under eviction", ebad==0);
    ok("store_check crc clean under paging", store_check(s, STORE_CHECK_CRC)==0);

    store_pool_stats(s, &st);
    printf("     after reads: resident=%zu (<= cap=%zu)  hits=%llu misses=%llu evictions=%llu\n",
           st.resident, st.cap, (unsigned long long)st.hits,
           (unsigned long long)st.misses, (unsigned long long)st.evictions);
    ok("still bounded after full read-back", st.resident <= st.cap);
    store_close(s);
    unlink(path);
}

/* ════════════════════════════════════════════════════════════════════════════
 * TEST 2 — EVICTION POLICY: a repeatedly-touched HOT set stays resident (0 extra
 * faults) while a streaming COLD set is evicted; and a dirty-heavy write burst
 * proves dirty pages are NEVER stolen before a checkpoint (no-steal).
 * ════════════════════════════════════════════════════════════════════════════ */
static void test_eviction_policy(void){
    printf("\n== 2) eviction policy: hot resident, cold evicted, no dirty stolen ==\n");
    char path[600]; path_in(path, sizeof path, "evict.store");
    unlink(path);

    /* ---- part A: hot vs cold ---- */
    EngramPagedStore* s = store_create(path);
    if (!s){ ok("store_create", 0); return; }
    const int N = 1500;
    for (int i=0;i<N;i++){ StoreNode n; gen_node(i,&n); store_put_node(s,&n); free_node_fields(&n);
        if ((i%400)==399) store_sync(s); }
    store_sync(s);
    store__set_pool_frames(s, 64);

    const int HOT = 8;
    /* warm the hot set */
    for (int h=0;h<HOT;h++){ char id[32]; snprintf(id,sizeof id,"node-%d",h);
        StoreNode g; if (store_get_node(s,id,&g)==1) store_node_free(&g); }

    StorePoolStats a,b;
    uint64_t hot_faults = 0, cold_faults = 0;
    int cold = 200;                            /* streaming cold ids well outside hot set */
    for (int r=0;r<150;r++){
        for (int h=0;h<HOT;h++){
            char id[32]; snprintf(id,sizeof id,"node-%d",h);
            store_pool_stats(s,&a);
            StoreNode g; if (store_get_node(s,id,&g)==1) store_node_free(&g);
            store_pool_stats(s,&b);
            hot_faults += (b.misses - a.misses);
        }
        for (int c=0;c<3;c++){
            char id[32]; snprintf(id,sizeof id,"node-%d",cold++);
            if (cold>=N) cold=200;
            store_pool_stats(s,&a);
            StoreNode g; if (store_get_node(s,id,&g)==1) store_node_free(&g);
            store_pool_stats(s,&b);
            cold_faults += (b.misses - a.misses);
        }
    }
    printf("     hot re-get faults (post-warm)=%llu   cold stream faults=%llu\n",
           (unsigned long long)hot_faults, (unsigned long long)cold_faults);
    ok("HOT pages stay resident (0 faults on re-access)", hot_faults == 0);
    ok("COLD pages get evicted + re-faulted", cold_faults > 0);
    store_pool_stats(s,&b);
    double hr = (double)b.hits / (double)(b.hits + b.misses);
    printf("     overall hit-rate = %.3f (hits=%llu misses=%llu)\n",
           hr, (unsigned long long)b.hits, (unsigned long long)b.misses);
    ok("hit-rate is sane (> 0.5)", hr > 0.5);
    store_close(s);
    unlink(path);

    /* ---- part B: no-steal (dirty pages never evicted before checkpoint) ---- */
    EngramPagedStore* s2 = store_create(path);
    if (!s2){ ok("store_create(2)", 0); return; }
    store__set_pool_frames(s2, 8);             /* tiny budget */
    for (int i=0;i<1200;i++){ StoreNode n; gen_node(i,&n); store_put_node(s2,&n); free_node_fields(&n); }
    /* NO sync: every mutated page is dirty and, by no-steal, unevictable */
    StorePoolStats d; store_pool_stats(s2,&d);
    printf("     tiny cap=%zu, unsynced burst: resident=%zu dirty=%zu evictions=%llu\n",
           d.cap, d.resident, d.dirty, (unsigned long long)d.evictions);
    ok("dirty pages pinned in RAM beyond budget (no-steal)", d.dirty > d.cap && d.resident > d.cap);
    /* a just-written node is served correctly from its dirty in-RAM page */
    { StoreNode want; gen_node(777,&want); StoreNode got; int hit=store_get_node(s2,want.id,&got);
      ok("read served correctly from dirty (un-flushed) page", hit==1 && cmp_node(&want,&got));
      if (hit==1) store_node_free(&got); free_node_fields(&want); }
    store_sync(s2);                            /* checkpoint → dirty become clean/evictable */
    store_pool_stats(s2,&d);
    ok("checkpoint cleared all dirty frames", d.dirty == 0);
    /* durability across reopen after the no-steal burst */
    store_close(s2);
    EngramPagedStore* s3 = store_open(path);
    store__set_pool_frames(s3, 8);
    int miss=0; for (int i=0;i<1200;i++){ StoreNode want; gen_node(i,&want);
        StoreNode got; int hit=store_get_node(s3,want.id,&got);
        if (hit!=1 || !cmp_node(&want,&got)) miss++;
        if (hit==1) store_node_free(&got); free_node_fields(&want); }
    ok("all 1200 survive reopen, bit-exact, tiny pool", miss==0);
    store_close(s3);
    unlink(path);
}

/* ════════════════════════════════════════════════════════════════════════════
 * TEST 3 — PINNED RESIDENCY: superblocks + index roots never evicted under heavy
 * thrash; an explicitly pinned page stays until unpinned; a pinned hot layer's
 * pages stay resident and are released on unpin.
 * ════════════════════════════════════════════════════════════════════════════ */
static void test_pinning(void){
    printf("\n== 3) pinned residency: superblocks / index roots / page / layer ==\n");
    char path[600]; path_in(path, sizeof path, "pin.store");
    unlink(path);
    EngramPagedStore* s = store_create(path);
    if (!s){ ok("store_create", 0); return; }
    const int N = 1500;
    for (int i=0;i<N;i++){ StoreNode n; gen_node(i,&n); store_put_node(s,&n); free_node_fields(&n);
        if ((i%400)==399) store_sync(s); }
    store_sync(s);
    store_close(s);

    s = store_open(path);                       /* reopen: SBs + roots auto-pinned */
    store__set_pool_frames(s, 24);

    uint64_t P = store_page_count(s) / 2;       /* an arbitrary interior page to pin */
    store_pin_page(s, P);

    /* thrash: stream a large cold working set to force heavy eviction */
    for (int pass=0; pass<3; pass++)
        for (int i=0;i<N;i++){ char id[32]; snprintf(id,sizeof id,"node-%d",i);
            StoreNode g; if (store_get_node(s,id,&g)==1) store_node_free(&g); }

    ok("superblock page 0 never evicted", store_pool_resident(s,0)==1);
    ok("superblock mirror page 1 never evicted", store_pool_resident(s,1)==1);
    ok("explicitly pinned page stayed resident under thrash", store_pool_resident(s,P)==1);

    StorePoolStats st; store_pool_stats(s,&st);
    printf("     after thrash: resident=%zu pinned=%zu evictions=%llu\n",
           st.resident, st.pinned, (unsigned long long)st.evictions);
    ok("structural + explicit pins counted (>=4: 2 SB + 2 roots)", st.pinned >= 4);

    /* unpin the page → it becomes evictable and is dropped under further thrash */
    store_unpin_page(s, P);
    for (int i=0;i<N;i++){ char id[32]; snprintf(id,sizeof id,"node-%d",i);
        StoreNode g; if (store_get_node(s,id,&g)==1) store_node_free(&g); }
    ok("unpinned page becomes evictable (dropped)", store_pool_resident(s,P)==0);

    /* hot-layer pin: layer 3 is used by ~1/5 of the nodes */
    int npin = store_pin_layer(s, 3);
    printf("     store_pin_layer(3) pinned %d page(s)\n", npin);
    ok("pin_layer pinned a non-empty page set", npin > 0);
    store_pool_stats(s,&st);
    size_t pinned_with_layer = st.pinned;
    for (int pass=0; pass<3; pass++)
        for (int i=0;i<N;i++){ char id[32]; snprintf(id,sizeof id,"node-%d",i);
            StoreNode g; if (store_get_node(s,id,&g)==1) store_node_free(&g); }
    store_pool_stats(s,&st);
    ok("hot-layer pages stay resident under thrash", st.pinned >= pinned_with_layer);
    ok("layer pin holds >= npin extra frames", st.pinned >= (size_t)npin + 4);

    store_unpin_layer(s, 3);
    store_pool_stats(s,&st);
    size_t after_unpin_max = st.pinned;
    for (int i=0;i<N;i++){ char id[32]; snprintf(id,sizeof id,"node-%d",i);
        StoreNode g; if (store_get_node(s,id,&g)==1) store_node_free(&g); }
    store_pool_stats(s,&st);
    printf("     pinned frames: with-layer=%zu  after-unpin=%zu\n", pinned_with_layer, st.pinned);
    ok("unpin_layer released the layer's pins", st.pinned < pinned_with_layer && after_unpin_max <= pinned_with_layer);

    store_close(s);
    unlink(path);
}

/* ════════════════════════════════════════════════════════════════════════════
 * TEST 4 — PREFETCH: a sequential scan faults far fewer times with read-ahead on
 * than off (each cold cache; identical store).
 * ════════════════════════════════════════════════════════════════════════════ */
static void test_prefetch(void){
    printf("\n== 4) prefetch: sequential scan faults fewer with read-ahead ==\n");
    char path[600]; path_in(path, sizeof path, "prefetch.store");
    unlink(path);
    EngramPagedStore* s = store_create(path);
    if (!s){ ok("store_create", 0); return; }
    for (int i=0;i<2000;i++){ StoreNode n; gen_node(i,&n); store_put_node(s,&n); free_node_fields(&n);
        if ((i%400)==399) store_sync(s); }
    store_sync(s);
    store_close(s);

    /* prefetch OFF — cold cache */
    EngramPagedStore* a = store_open(path);
    store__set_pool_frames(a, 0);               /* unlimited: isolate prefetch, no eviction */
    store__set_prefetch(a, 0);
    StorePoolStats o0, o1; store_pool_stats(a,&o0);
    int na = store_scan_nodes(a, noop_node_cb, NULL);   /* walk + fault every page */
    (void)na;
    store_pool_stats(a,&o1);
    uint64_t faults_off = o1.misses - o0.misses;
    store_close(a);

    /* prefetch ON — cold cache (fresh open) */
    EngramPagedStore* b = store_open(path);
    store__set_pool_frames(b, 0);
    store__set_prefetch(b, 16);
    StorePoolStats p0, p1; store_pool_stats(b,&p0);
    int nb = store_scan_nodes(b, noop_node_cb, NULL);
    (void)nb;
    store_pool_stats(b,&p1);
    uint64_t faults_on  = p1.misses - p0.misses;
    uint64_t pref_reads = p1.prefetch_reads - p0.prefetch_reads;
    store_close(b);

    printf("     scan demand-faults: prefetch OFF=%llu  ON=%llu  (read-ahead brought in %llu pages)\n",
           (unsigned long long)faults_off, (unsigned long long)faults_on,
           (unsigned long long)pref_reads);
    ok("prefetch reduced demand faults", faults_on < faults_off);
    ok("read-ahead actually ran", pref_reads > 0);
    unlink(path);
}

/* ════════════════════════════════════════════════════════════════════════════
 * TEST 5 — CRASH SAFETY UNDER PAGING: WAL replay and checkpoint-crash recovery
 * with a tiny pool (pages evict + re-fault during replay).
 * ════════════════════════════════════════════════════════════════════════════ */
static void test_crash_under_paging(void){
    printf("\n== 5) crash safety under a tiny pool (ENGRAM_POOL_FRAMES=16) ==\n");
    setenv("ENGRAM_POOL_FRAMES", "16", 1);      /* every engram_open() below is paged */
    setenv("ENGRAM_WAL_SYNC", "always", 1);

    /* ---- 5a: power-loss → WAL replay ---- */
    char dir[600]; path_in(dir, sizeof dir, "crash_wal"); mkdir(dir, 0700);
    EngramPagedStore* s = engram_open(dir);
    if (!s){ ok("engram_open", 0); return; }
    const int M = 400;
    for (int i=0;i<M;i++){ StoreNode n; gen_node(i,&n); store_put_node(s,&n); free_node_fields(&n); }
    store__crash(s);                             /* abandon RAM (dirty pages lost); WAL fsync'd */
    s = engram_open(dir);                        /* replay WAL under 16-frame pool */
    ok("reopened after crash (WAL replay, tiny pool)", s!=NULL);
    int bad=0; for (int i=0;i<M;i++){ StoreNode want; gen_node(i,&want);
        StoreNode got; int hit=store_get_node(s,want.id,&got);
        if (hit!=1 || !cmp_node(&want,&got)) bad++;
        if (hit==1) store_node_free(&got); free_node_fields(&want); }
    ok("all 400 nodes recovered bit-exact via WAL replay under paging", bad==0);
    ok("store_check crc clean post-recovery", store_check(s, STORE_CHECK_CRC)==0);
    engram_close(s);

    /* ---- 5b: checkpoint-crash at each phase ---- */
    for (int phase=0; phase<=4; phase++){
        char cdir[620]; snprintf(cdir, sizeof cdir, "%s/ck%d", g_dir, phase); mkdir(cdir,0700);
        EngramPagedStore* c = engram_open(cdir);
        for (int i=0;i<CK_NODES;i++){ StoreNode n; gen_node(i,&n); store_put_node(c,&n); free_node_fields(&n); }
        store__checkpoint_crashat(c, phase);     /* crash mid-checkpoint (frees c) */
        EngramPagedStore* r = engram_open(cdir); /* heal + replay under tiny pool */
        int miss=0; for (int i=0;i<CK_NODES;i++){ StoreNode want; gen_node(i,&want);
            StoreNode got; int hit=store_get_node(r,want.id,&got);
            if (hit!=1 || !cmp_node(&want,&got)) miss++;
            if (hit==1) store_node_free(&got); free_node_fields(&want); }
        char nm[64]; snprintf(nm,sizeof nm,"checkpoint-crash phase %d: all recovered (paged)", phase);
        ok(nm, miss==0);
        engram_close(r);
    }
    unsetenv("ENGRAM_POOL_FRAMES");
}

/* ════════════════════════════════════════════════════════════════════════════
 * TEST 6 — DEFAULT POOL == PHASE 1: with the default (large) budget, no eviction
 * ever fires; the whole store is resident, exactly the pre-M4 behaviour.
 * ════════════════════════════════════════════════════════════════════════════ */
static void test_default_is_phase1(void){
    printf("\n== 6) default (large) pool == Phase-1 resident (no eviction) ==\n");
    char path[600]; path_in(path, sizeof path, "default.store");
    unlink(path);
    EngramPagedStore* s = store_create(path);   /* default cap, no override */
    if (!s){ ok("store_create", 0); return; }
    for (int i=0;i<1500;i++){ StoreNode n; gen_node(i,&n); store_put_node(s,&n); free_node_fields(&n); }
    store_sync(s);
    for (int i=0;i<1500;i++){ char id[32]; snprintf(id,sizeof id,"node-%d",i);
        StoreNode g; if (store_get_node(s,id,&g)==1) store_node_free(&g); }
    StorePoolStats st; store_pool_stats(s,&st);
    printf("     cap=%zu resident=%zu evictions=%llu  (pages=%llu)\n",
           st.cap, st.resident, (unsigned long long)st.evictions,
           (unsigned long long)store_page_count(s));
    ok("default budget is large", st.cap >= (size_t)(1u<<20));
    ok("no eviction ever fired at default budget", st.evictions == 0);
    ok("whole store resident (every page cached)", st.resident == store_page_count(s));
    store_close(s);
    unlink(path);
}

int main(void){
    mk_dir();
    printf("engram M4 buffer-pool gate — dir=%s\n", g_dir);
    test_small_pool_roundtrip();
    test_eviction_policy();
    test_pinning();
    test_prefetch();
    test_crash_under_paging();
    test_default_is_phase1();
    printf("\n================  %d passed, %d failed  ================\n", g_pass, g_fail);
    return g_fail ? 1 : 0;
}