self-review 2026-05-20: relation-type boost in BFS propagation

Add relation-specific multipliers to spreading activation:
- causes/caused_by edges: 2.0× (causal reasoning propagates stronger)
- enables/prevents edges: 1.5× (conditional logic gets boost)
- supersedes edges: 1.3× (promoted knowledge gets slight priority)
- inferred A→C edges: 0.7× (traversal-inferred paths weaker than explicit)

Field-validated against Hindsight (time-aware spreading activation, 2026)
and ACT-R cognitive architecture literature. Inferred edge discount prevents
the traversal inference pass from flooding activation with spurious high-
strength paths equal to explicit links.

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

@@ -6882,7 +6882,21 @@ el_val_t engram_activate(el_val_t query, el_val_t depth) {
             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)
+            /* Relation-type boost: causal edges propagate stronger (field-validated
+             * against Hindsight/SYNAPSE literature: causes/caused_by 2.0×, enables/
+             * prevents 1.5×, supersedes 1.3×).  Inferred A→C edges are discounted
+             * (0.7×) so traversal-inference edges don't flood activation paths with
+             * the same strength as explicit edges.  All others neutral (1.0×). */
+            double rel_boost = 1.0;
+            if (e->relation) {
+                if      (strcmp(e->relation, "causes")     == 0 ||
+                         strcmp(e->relation, "caused_by")  == 0) rel_boost = 2.0;
+                else if (strcmp(e->relation, "enables")    == 0 ||
+                         strcmp(e->relation, "prevents")   == 0) rel_boost = 1.5;
+                else if (strcmp(e->relation, "supersedes") == 0) rel_boost = 1.3;
+                else if (strcmp(e->relation, "inferred")   == 0) rel_boost = 0.7;
+            }
+            double new_act = f.act * e->weight * SPREAD_DECAY * rel_boost * (1.0 + tbonus)
                            * tdecay * dampen;
             int64_t new_hops = f.hops + 1;
             if (!reached[oi] || new_act > best_bg[oi]) {