engram: ranked BM25+recency search replaces storage-order substring; URL-decode GET query params

Measured on the live container mind (pinned 40-query eval, judged): substring
2/40=5% hit@5 -> ranked 35/40=88%. Multi-word queries stop returning zero; new
memories stop losing to storage order (created_at tiebreak). Transparent-layer
identity filter preserved in both passes; jb_finish (#64) tail preserved.
query_param now url_decode()s values - %XX arrived literal before (pre-existing
GET defect, masked while multi-word substring returned nothing anyway).
E2E-verified in Tim's container deployment 2026-07-14/15; eval harness:
docs repo research-archive/p0-prototypes/eval_pinned_40q_20260715.py.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

engram/src/server.el

@@ -50,8 +50,12 @@ fn query_param(path: String, key: String) -> String {
     if pos < 0 { return "" }
     let after: String = str_slice(qs, pos + str_len(needle), str_len(qs))
     let amp: Int = str_index_of(after, "&")
-    if amp < 0 { return after }
-    str_slice(after, 0, amp)
+    // SPEC-SEARCH-UPGRADE 2026-07-14: URL-decode the extracted value (%XX and
+    // '+' were previously passed through literally, so an encoded multi-word
+    // query arrived as junk tokens — pre-existing GET-path defect, masked
+    // until search could actually rank multi-word queries).
+    if amp < 0 { return url_decode(after) }
+    url_decode(str_slice(after, 0, amp))
 }
 
 fn query_int(path: String, key: String, default_val: Int) -> Int {

lang/el-compiler/runtime/el_runtime.c

@@ -6826,6 +6826,116 @@ static int istr_contains(const char* hay, const char* needle) {
     return 0;
 }
 
+/* ---- SPEC-SEARCH-UPGRADE-OURS-2026-07-14: ranked search (BM25 + recency) ----
+ * Replaces first-N-in-storage-order substring matching (measured 13% hit@5 on
+ * the 15-query pinned eval; ranked model measured 93% offline). Deterministic,
+ * local, transparent — no model call on the hot path. Multi-word queries score
+ * per-token (rare+concentrated terms weigh most); ties break newest-first so
+ * fresh memories stop losing to storage order. The transparent-layer identity
+ * filter is preserved unchanged: hidden self layers stay invisible here and
+ * surface only via engram_activate — the legitimate path. */
+
+#define ENGRAM_BM25_MAX_QTOK 16
+#define ENGRAM_BM25_TOKLEN   48
+
+static int engram_tok_next(const char** ps, char* out, int cap) {
+    const char* s = *ps;
+    while (*s && !isalnum((unsigned char)*s)) s++;
+    if (!*s) { *ps = s; return 0; }
+    int n = 0;
+    while (*s && isalnum((unsigned char)*s)) {
+        if (n < cap - 1) out[n++] = (char)tolower((unsigned char)*s);
+        s++;
+    }
+    out[n] = 0; *ps = s; return 1;
+}
+
+static void engram_field_stats(const char* field,
+                               char qtok[][ENGRAM_BM25_TOKLEN], int nq,
+                               int64_t* tf, int64_t* doclen) {
+    if (!field) return;
+    char buf[ENGRAM_BM25_TOKLEN];
+    const char* p = field;
+    while (engram_tok_next(&p, buf, sizeof buf)) {
+        (*doclen)++;
+        for (int t = 0; t < nq; t++)
+            if (strcmp(buf, qtok[t]) == 0) tf[t]++;
+    }
+}
+
+typedef struct { double score; int64_t created; int64_t idx; } EngramHit;
+
+static int engram_hit_cmp(const void* a, const void* b) {
+    const EngramHit* x = (const EngramHit*)a;
+    const EngramHit* y = (const EngramHit*)b;
+    if (x->score != y->score) return (x->score < y->score) ? 1 : -1;
+    if (x->created != y->created) return (x->created < y->created) ? 1 : -1;
+    return 0;
+}
+
+/* Scores every visible node against the query; writes ranked hits into `out`
+ * (caller allocates g->node_count entries). Returns min(hits, lim). */
+static int64_t engram_search_ranked(EngramStore* g, const char* q, int64_t lim,
+                                    EngramHit* out) {
+    char qtok[ENGRAM_BM25_MAX_QTOK][ENGRAM_BM25_TOKLEN];
+    int nq = 0;
+    {
+        const char* p = q; char buf[ENGRAM_BM25_TOKLEN];
+        while (nq < ENGRAM_BM25_MAX_QTOK && engram_tok_next(&p, buf, sizeof buf)) {
+            int dup = 0;
+            for (int t = 0; t < nq; t++)
+                if (strcmp(qtok[t], buf) == 0) { dup = 1; break; }
+            if (!dup) { strcpy(qtok[nq], buf); nq++; }
+        }
+    }
+    if (nq == 0) return 0;
+
+    int64_t N = g->node_count;
+    int64_t* tfm  = (int64_t*)calloc((size_t)(N * nq), sizeof(int64_t));
+    int64_t* dlen = (int64_t*)calloc((size_t)N, sizeof(int64_t));
+    if (!tfm || !dlen) { free(tfm); free(dlen); return 0; }
+    int64_t df[ENGRAM_BM25_MAX_QTOK] = {0};
+    double total_len = 0.0; int64_t live = 0;
+    for (int64_t i = 0; i < N; i++) {
+        EngramNode* n = &g->nodes[i];
+        if (engram_layer_is_transparent(n->layer_id)) continue;
+        live++;
+        int64_t* tf = &tfm[i * nq];
+        engram_field_stats(n->content, qtok, nq, tf, &dlen[i]);
+        engram_field_stats(n->label,   qtok, nq, tf, &dlen[i]);
+        engram_field_stats(n->tags,    qtok, nq, tf, &dlen[i]);
+        total_len += (double)dlen[i];
+        for (int t = 0; t < nq; t++) if (tf[t] > 0) df[t]++;
+    }
+    double avg = (live > 0) ? total_len / (double)live : 1.0;
+    if (avg <= 0.0) avg = 1.0;
+    const double k1 = 1.2, b = 0.75;
+    int64_t nhits = 0;
+    for (int64_t i = 0; i < N; i++) {
+        EngramNode* n = &g->nodes[i];
+        if (engram_layer_is_transparent(n->layer_id)) continue;
+        int64_t* tf = &tfm[i * nq];
+        double s = 0.0;
+        for (int t = 0; t < nq; t++) {
+            if (tf[t] == 0) continue;
+            double idf = log(((double)live - (double)df[t] + 0.5) /
+                             ((double)df[t] + 0.5) + 1.0);
+            double tfd = (double)tf[t];
+            s += idf * (tfd * (k1 + 1.0)) /
+                 (tfd + k1 * (1.0 - b + b * (double)dlen[i] / avg));
+        }
+        if (s > 0.0) {
+            out[nhits].score = s;
+            out[nhits].created = n->created_at;
+            out[nhits].idx = i;
+            nhits++;
+        }
+    }
+    free(tfm); free(dlen);
+    qsort(out, (size_t)nhits, sizeof(EngramHit), engram_hit_cmp);
+    return (nhits < lim) ? nhits : lim;
+}
+
 el_val_t engram_search(el_val_t query, el_val_t limit) {
     EngramStore* g = engram_get();
     const char* q = EL_CSTR(query);
@@ -6833,21 +6943,13 @@ el_val_t engram_search(el_val_t query, el_val_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++;
-        }
-    }
+    if (g->node_count == 0) return lst;
+    EngramHit* hits = (EngramHit*)malloc((size_t)g->node_count * sizeof(EngramHit));
+    if (!hits) return lst;
+    int64_t k = engram_search_ranked(g, q, lim, hits);
+    for (int64_t i = 0; i < k; i++)
+        lst = el_list_append(lst, engram_node_to_map(&g->nodes[hits[i].idx]));
+    free(hits);
     return lst;
 }
 
@@ -7762,27 +7864,23 @@ el_val_t engram_get_node_json(el_val_t id) {
 }
 
 el_val_t engram_search_json(el_val_t query, el_val_t limit) {
+    /* SPEC-SEARCH-UPGRADE 2026-07-14: same ranked BM25+recency core as
+     * engram_search; transparent-layer identity filter enforced inside it. */
     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++;
+    if (q && *q && g->node_count > 0) {
+        EngramHit* hits = (EngramHit*)malloc((size_t)g->node_count * sizeof(EngramHit));
+        if (hits) {
+            int64_t k = engram_search_ranked(g, q, lim, hits);
+            for (int64_t i = 0; i < k; i++) {
+                if (i) jb_putc(&b, ',');
+                engram_emit_node_json(&b, &g->nodes[hits[i].idx]);
             }
+            free(hits);
         }
     }
     jb_putc(&b, ']');