self-review 2026-08-15: consolidate the strongest Hebbian candidate, not the lowest-hash one

The link-formation scan walked candidate slots ascending and stopped at
ENGRAM_HEBB_LINK_PER_CALL (2). Slot index is a hash of the node id pair, so
whenever more than two candidates cleared LINK_MIN in the same call, the two
consolidated were the two with the lowest hash and a stronger association
waited - indefinitely, since the scan restarts from slot 0 every call while
the leader decays at ENGRAM_HEBB_DECAY.

Measured 08-13..08-15: hebb_cand_max peaked at 0.4963, 3.3x LINK_MIN, during
a ~14h stretch of continuous qualification at the 2/call cap.

Same defect the 2026-08-02 review named and fixed for breakthrough weights
(index order is not a cognitive criterion), never carried across to the one
path that writes permanent structure - and there is no pruning path, so
growth is one-way. Selection pressure matters most where the result is
irreversible.

No-op when <=2 candidates qualify; picks the best when more do.

lang/releases/v1.0.0-20260501/el_runtime.c

@@ -9775,11 +9775,65 @@ el_val_t engram_activate(el_val_t query, el_val_t depth) {
                 }
                 int64_t hebb_edge_cap =
                     (int64_t)((double)g->edge_count * ENGRAM_HEBB_LINK_MAX_FRAC);
-                for (int s = 0; s < ENGRAM_HEBB_CAND_SLOTS
+                /* Select the STRONGEST qualifying candidates, not the first
-                                && formed < ENGRAM_HEBB_LINK_PER_CALL
+                 * ones in hash-slot order (2026-08-15 self-review).
-                                && hebb_edge_total < hebb_edge_cap; s++) {
+                 *
-                    EgHebbCand* c = &_eg_hebb_cand[s];
+                 * This loop used to scan slots ascending and stop at
-                    if (!c->a || c->score < ENGRAM_HEBB_LINK_MIN) continue;
+                 * ENGRAM_HEBB_LINK_PER_CALL (2). Slot index is
+                 * engram_id_hash(lo)*1000003 ^ engram_id_hash(hi) mod 8192 —
+                 * i.e. arbitrary with respect to association strength. So
+                 * whenever more than two candidates cleared LINK_MIN in the
+                 * same call, the two that got consolidated were the two with
+                 * the LOWEST HASH, and a stronger association simply waited.
+                 * It waited indefinitely, not just one round: the scan
+                 * restarts from slot 0 every call, so a low-slot candidate
+                 * that re-qualifies keeps winning the same race, while the
+                 * leader decays at ENGRAM_HEBB_DECAY the whole time.
+                 *
+                 * Measured on this store over the 08-13→08-15 window:
+                 * hebb_cand_max peaked at 0.4963 (08-14 06:57) — 3.3x
+                 * LINK_MIN — during a ~14h stretch when candidates were
+                 * qualifying continuously and links were being formed at the
+                 * ≤2/call cap. The system was consolidating the associations
+                 * it happened to reach first, while the association it had
+                 * most strongly learned sat unconsolidated.
+                 *
+                 * This is the same defect the 2026-08-02 self-review named
+                 * and fixed for breakthrough weights — "the tie-break at the
+                 * cutoff degenerated to node-array index order, which is not
+                 * a cognitive criterion" — but that fix was never carried
+                 * across to link formation, which is the one path that writes
+                 * PERMANENT structure. A wrong breakthrough costs one WM slot
+                 * for one call; a wrong consolidation is an edge that never
+                 * goes away (ENGRAM_HEBB_LINK_MAX_FRAC notes there is no
+                 * pruning path — growth is one-way). Selection pressure
+                 * matters most exactly where the result is irreversible.
+                 *
+                 * Cost: PER_CALL(2) x 8192 comparisons of a double, against an
+                 * O(edge_count) relation scan (37k+) immediately above and an
+                 * O(edge_count) eg_edge_exists_between per edge formed. Noise.
+                 *
+                 * Invalid winners (node deleted, edge already present) are
+                 * cleared and do NOT consume one of the two slots — same as
+                 * the old `continue`. Clearing strictly shrinks the candidate
+                 * set, so the retry loop always terminates. */
+                while (formed < ENGRAM_HEBB_LINK_PER_CALL
+                       && hebb_edge_total < hebb_edge_cap) {
+                    int best_s = -1;
+                    double best_score = 0.0;
+                    for (int s = 0; s < ENGRAM_HEBB_CAND_SLOTS; s++) {
+                        EgHebbCand* cs = &_eg_hebb_cand[s];
+                        if (!cs->a) continue;
+                        if (cs->score < ENGRAM_HEBB_LINK_MIN) continue;
+                        /* strict > keeps the lowest slot on an exact tie, so
+                         * selection stays deterministic across runs */
+                        if (best_s < 0 || cs->score > best_score) {
+                            best_score = cs->score;
+                            best_s = s;
+                        }
+                    }
+                    if (best_s < 0) break;   /* nothing qualifies this call */
+                    EgHebbCand* c = &_eg_hebb_cand[best_s];
                     if (engram_idmap_get(g, c->a) < 0 ||
                         engram_idmap_get(g, c->b) < 0) { /* node gone */
                         eg_hebb_slot_clear(c); continue;