fix(reliability): engram-write — guard all fire-and-forget writes

Every engram_node_full call that dropped its return value now binds it
and emits a println on empty string. engram_save calls in consolidate,
heartbeat, and dharma-room-turn are checked for failure. The two API
handlers (log_state_event, tune_config) that skipped api_persisted()
now match the read-back-after-write contract used everywhere else in
neuron-api.el.

Files changed:
- chat.el: conv_history_persist, handle_dharma_room_turn, auto_persist
- soul.el: emit_session_start_event, seed_persona_from_env HTTP check
- memory.el: mem_save, mem_boot_count_inc
- neuron-api.el: handle_api_log_state_event, handle_api_tune_config,
  handle_api_consolidate (engram_save + session summary write)
- awareness.el: ise_post local-engram fallback path

TODO comments added for non-atomic patterns (issues #12, #13) and
the missing circuit breaker (#14) — these require new primitives.

neuron-api.el

@@ -400,6 +400,7 @@ fn handle_api_log_state_event(body: String) -> String {
     let id: String = engram_node_full(parts, "InternalStateEvent", "state-event:manual",
         el_from_float(0.85), el_from_float(0.85), el_from_float(0.9),
         "Episodic", tags)
+    if !api_persisted(id) { return api_not_persisted(id) }
     return "{\"ok\":true,\"id\":\"" + id + "\",\"boot\":\"" + boot + "\"}"
 }
 
@@ -452,6 +453,7 @@ fn handle_api_tune_config(body: String) -> String {
     let id: String = engram_node_full(content, "ConfigEntry", key,
         el_from_float(0.85), el_from_float(0.85), el_from_float(0.9),
         "Canonical", tags)
+    if !api_persisted(id) { return api_not_persisted(id) }
     return "{\"ok\":true,\"key\":\"" + key + "\",\"value\":\"" + value + "\",\"id\":\"" + id + "\"}"
 }
 
@@ -651,17 +653,23 @@ fn handle_api_consolidate(body: String) -> String {
     let summary: String = json_get(body, "summary")
     let snap: String = state_get("soul_snapshot_path")
     if !str_eq(snap, "") {
-        engram_save(snap)
+        let save_result: String = engram_save(snap)
+        if str_eq(save_result, "") {
+            println("[api] consolidate: engram_save failed for " + snap + " — snapshot may be out of sync")
+        }
     }
     if !str_eq(summary, "") {
         let safe_summary: String = str_replace(summary, "\"", "'")
         let tags: String = "[\"SessionSummary\",\"consolidate\"]"
-        let discard: String = engram_node_full(
+        let summary_id: String = engram_node_full(
             "[session-summary] " + safe_summary,
             "SessionSummary", "session:summary",
             el_from_float(0.7), el_from_float(0.7), el_from_float(0.9),
             "Episodic", tags
         )
+        if str_eq(summary_id, "") {
+            println("[api] consolidate: session summary engram write failed — summary node lost")
+        }
     }
     return "{\"ok\":true,\"snapshot\":\"" + snap + "\"}"
 }