self-review 2026-07-22: ACT-R/Petrov base-level WM decay replaces per-call multiplicative carry-over

The old carry-over (weight *= 0.7 per engram_activate call) was call-rate-
dependent — carried context died in seconds under rapid curiosity scans and
lingered for hours under quiet loops — and a decayed scalar cannot represent
access frequency at all.

Now: k=10 access-timestamp ring + Petrov (2006) closed-form tail, d=0.5.
WM promotion and engram_strengthen record presentations; carry-over evicts
at base-level tau=-3.0 (Soar forgetting, ~403s single-touch) and shapes the
weight held at promotion (wm_anchor) with the ACT-R retrieval logistic
(s=0.4) — a pure function of wall-clock time, idempotent per call.
Persisted as access_ts/wm_anchor in snapshots; legacy nodes fall back to
the optimized form ln(n/(1-d)) - d*ln(L). base_level exposed in both node
serializers for observability.

Backing spec: 2026-07-21 integration brief (bl-b17facdd). Verified live:
carried weight ~anchor seconds after two disjoint activations (old code:
0.49x); frequency-hot nodes hold B=1.9 vs -0.14 single-touch.

engram/dist/engram.c

@@ -24,6 +24,7 @@ el_val_t route_save(el_val_t method, el_val_t path, el_val_t body);
 el_val_t route_load(el_val_t method, el_val_t path, el_val_t body);
 el_val_t route_health(el_val_t method, el_val_t path, el_val_t body);
 el_val_t route_sync(el_val_t method, el_val_t path, el_val_t body);
+el_val_t route_load_merge(el_val_t method, el_val_t path, el_val_t body);
 el_val_t route_emit_ise(el_val_t method, el_val_t path, el_val_t body);
 el_val_t route_capture_knowledge(el_val_t method, el_val_t path, el_val_t body);
 el_val_t check_auth_ok(el_val_t method, el_val_t body);
@@ -35,6 +36,7 @@ el_val_t port;
 el_val_t data_dir_raw;
 el_val_t data_dir;
 el_val_t snapshot_path;
+el_val_t boot_snap;
 
 el_val_t parse_port(el_val_t bind) {
   el_val_t colon = str_index_of(bind, EL_STR(":"));
@@ -147,7 +149,7 @@ el_val_t route_scan_nodes(el_val_t method, el_val_t path, el_val_t body) {
 el_val_t route_scan_edges(el_val_t method, el_val_t path, el_val_t body) {
   el_val_t dir_raw = env(EL_STR("ENGRAM_DATA_DIR"));
   el_val_t dir = ({ el_val_t _if_result_3 = 0; if (str_eq(dir_raw, EL_STR(""))) { _if_result_3 = (EL_STR("/tmp/engram")); } else { _if_result_3 = (dir_raw); } _if_result_3; });
-  el_val_t snap_path = el_str_concat(dir, EL_STR("/snapshot.json"));
+  el_val_t snap_path = el_str_concat(dir, EL_STR("/.scan-export.json"));
   engram_save(snap_path);
   el_val_t snap = fs_read(snap_path);
   if (str_eq(snap, EL_STR(""))) {
@@ -252,7 +254,7 @@ el_val_t route_health(el_val_t method, el_val_t path, el_val_t body) {
 el_val_t route_sync(el_val_t method, el_val_t path, el_val_t body) {
   el_val_t dir_raw = env(EL_STR("ENGRAM_DATA_DIR"));
   el_val_t dir = ({ el_val_t _if_result_16 = 0; if (str_eq(dir_raw, EL_STR(""))) { _if_result_16 = (EL_STR("/tmp/engram")); } else { _if_result_16 = (dir_raw); } _if_result_16; });
-  el_val_t snap_path = el_str_concat(dir, EL_STR("/snapshot.json"));
+  el_val_t snap_path = el_str_concat(dir, EL_STR("/.sync-export.json"));
   engram_save(snap_path);
   el_val_t snap = fs_read(snap_path);
   if (str_eq(snap, EL_STR(""))) {
@@ -262,6 +264,23 @@ el_val_t route_sync(el_val_t method, el_val_t path, el_val_t body) {
   return 0;
 }
 
+el_val_t route_load_merge(el_val_t method, el_val_t path, el_val_t body) {
+  el_val_t p = json_get_string(body, EL_STR("path"));
+  if (str_eq(p, EL_STR(""))) {
+    return err_json(EL_STR("path is required"));
+  }
+  if (str_eq(fs_read(p), EL_STR(""))) {
+    return err_json(EL_STR("file missing or empty"));
+  }
+  el_val_t before_n = engram_node_count();
+  el_val_t before_e = engram_edge_count();
+  engram_load_merge(p);
+  el_val_t added_n = (engram_node_count() - before_n);
+  el_val_t added_e = (engram_edge_count() - before_e);
+  return el_str_concat(el_str_concat(el_str_concat(el_str_concat(el_str_concat(el_str_concat(EL_STR("{\"ok\":true,\"nodes_added\":"), int_to_str(added_n)), EL_STR(",\"edges_added\":")), int_to_str(added_e)), EL_STR(",\"node_count\":")), int_to_str(engram_node_count())), EL_STR("}"));
+  return 0;
+}
+
 el_val_t route_emit_ise(el_val_t method, el_val_t path, el_val_t body) {
   el_val_t content = json_get_string(body, EL_STR("content"));
   if (str_eq(content, EL_STR(""))) {
@@ -385,6 +404,9 @@ el_val_t handle_request(el_val_t method, el_val_t path, el_val_t body) {
   if (str_eq(method, EL_STR("POST")) && (str_eq(clean, EL_STR("/api/load")) || str_eq(clean, EL_STR("/load")))) {
     return route_load(method, path, body);
   }
+  if (str_eq(method, EL_STR("POST")) && (str_eq(clean, EL_STR("/api/load-merge")) || str_eq(clean, EL_STR("/load-merge")))) {
+    return route_load_merge(method, path, body);
+  }
   if (str_eq(method, EL_STR("GET")) && str_eq(clean, EL_STR("/api/sync"))) {
     return route_sync(method, path, body);
   }
@@ -401,6 +423,15 @@ int main(int _argc, char** _argv) {
   data_dir = ({ el_val_t _if_result_25 = 0; if (str_eq(data_dir_raw, EL_STR(""))) { _if_result_25 = (EL_STR("/tmp/engram")); } else { _if_result_25 = (data_dir_raw); } _if_result_25; });
   snapshot_path = el_str_concat(data_dir, EL_STR("/snapshot.json"));
   engram_load(snapshot_path);
+  boot_snap = fs_read(snapshot_path);
+  if (!str_eq(boot_snap, EL_STR(""))) {
+    if (engram_node_count() == 0) {
+      println(EL_STR("[engram] WARNING: snapshot.json is non-empty but load produced 0 nodes \xe2\x80\x94 preserving copy at snapshot.failed-load.json"));
+      fs_write(el_str_concat(data_dir, EL_STR("/snapshot.failed-load.json")), boot_snap);
+    } else {
+      fs_write(el_str_concat(data_dir, EL_STR("/snapshot.boot-backup.json")), boot_snap);
+    }
+  }
   println(EL_STR("[engram] runtime-native graph engine"));
   println(el_str_concat(EL_STR("[engram] data_dir="), data_dir));
   println(el_str_concat(EL_STR("[engram] node_count="), int_to_str(engram_node_count())));