fix(reliability): replace undefined session_exists with session_get check

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.

awareness.el

@@ -23,11 +23,14 @@ fn ise_post(content: String) -> Void {
     let ise_url: String = env("SOUL_ISE_URL")
     let engram_url: String = if str_eq(ise_url, "") { state_get("soul_engram_url") } else { ise_url }
     if str_eq(engram_url, "") {
-        let discard: String = engram_node_full(
+        let local_id: String = engram_node_full(
             content, "InternalStateEvent", "state-event",
             el_from_float(0.3), el_from_float(0.3), el_from_float(0.8),
             "Episodic", "[\"internal-state\",\"InternalStateEvent\"]"
         )
+        if str_eq(local_id, "") {
+            println("[awareness] ise_post: local engram_node_full failed — ISE lost")
+        }
         return ""
     }
     // Proper JSON string escaping: backslashes first, then quotes, then control chars.

chat.el

@@ -130,11 +130,14 @@ fn conv_history_persist(hist: String) -> Void {
     if str_eq(hist, "[]") { return "" }
     let ts: Int = time_now()
     let tags: String = "[\"conv-history\",\"persistent\"]"
-    let discard: String = engram_node_full(
+    let node_id: String = engram_node_full(
         hist, "Conversation", "conv:history",
         el_from_float(0.7), el_from_float(0.8), el_from_float(0.9),
         "Episodic", tags
     )
+    if str_eq(node_id, "") {
+        println("[chat] conv_history_persist: engram_node_full returned empty — history node lost")
+    }
 }
 
 // conv_history_load — restore conversation history from engram on first access.
@@ -637,6 +640,21 @@ fn handle_chat_agentic(body: String) -> String {
     // Thread-aware activation: same logic as handle_chat.
     // Use the session's or global history to anchor short messages to the thread.
     let req_session: String = json_get(body, "session_id")
+
+    // ISSUE #6/#7: validate that the session_id actually exists before proceeding.
+    // Without this check the loop silently treats any unknown/fabricated session_id
+    // as a fresh session — history loads as empty and no error is returned to the caller.
+    // Only validate when a session_id is explicitly provided; anonymous calls
+    // (no session_id) continue to work for backward compatibility.
+    let session_valid: Bool = if str_eq(req_session, "") {
+        true
+    } else {
+        !str_contains(session_get(req_session), "\"error\"")
+    }
+    if !session_valid {
+        return "{\"error\":\"session not found\",\"session_id\":\"" + req_session + "\",\"reply\":\"\"}"
+    }
+
     let hist_key: String = if str_eq(req_session, "") { "conv_history" } else { "session_hist_" + req_session }
     let agentic_hist: String = state_get(hist_key)
     let agentic_hist_len: Int = if str_eq(agentic_hist, "") { 0 } else { json_array_len(agentic_hist) }
@@ -1054,13 +1072,19 @@ fn handle_dharma_room_turn(body: String) -> String {
     // engram_node(content, "episodic", ...) which wrongly put a TIER into the node_type
     // slot — that's why nodes showed node_type="episodic". Use the full, correct contract.)
     let utterance_tags: String = "[\"soul-utterance\",\"episodic\"]"
-    let discard_id: String = engram_node_full(
+    let utterance_id: String = engram_node_full(
         clean_response, "Conversation", "soul:utterance",
         el_from_float(0.6), el_from_float(0.6), el_from_float(0.8),
         "Episodic", utterance_tags
     )
+    if str_eq(utterance_id, "") {
+        println("[chat] handle_dharma_room_turn: utterance engram write failed — node lost")
+    }
     if !str_eq(snap_path, "") {
-        let discard_save: String = engram_save(snap_path)
+        let save_result: String = engram_save(snap_path)
+        if str_eq(save_result, "") {
+            println("[chat] handle_dharma_room_turn: engram_save failed for " + snap_path)
+        }
     }
 
     let safe_response: String = json_safe(clean_response)
@@ -1142,7 +1166,7 @@ fn auto_persist(req: String, resp: String) -> Void {
         + ",\"label\":\"chat:" + ts_str + "\"}"
 
     let tags: String = "[\"Conversation\",\"chat\",\"timestamped\"]"
-    engram_node_full(
+    let persist_id: String = engram_node_full(
         content,
         "Conversation",
         "chat:" + ts_str,
@@ -1152,6 +1176,9 @@ fn auto_persist(req: String, resp: String) -> Void {
         "Episodic",
         tags
     )
+    if str_eq(persist_id, "") {
+        println("[chat] auto_persist: engram_node_full returned empty — conversation node lost (ts=" + ts_str + ")")
+    }
 }
 
 // strengthen_chat_nodes — strengthen the engram nodes that were activated during a chat.

memory.el

@@ -46,7 +46,10 @@ fn mem_consolidate() -> String {
 }
 
 fn mem_save(path: String) -> Void {
-    engram_save(path)
+    let save_result: String = engram_save(path)
+    if str_eq(save_result, "") {
+        println("[memory] mem_save: engram_save failed for " + path + " — snapshot may be incomplete")
+    }
 }
 
 fn mem_load(path: String) -> Void {
@@ -76,11 +79,14 @@ fn mem_boot_count_inc() -> Int {
     let next: Int = current + 1
     let content: String = "soul:boot_count:" + int_to_str(next)
     let tags: String = "[\"soul-meta\",\"boot-counter\"]"
-    let discard: String = engram_node_full(
+    let boot_node_id: String = engram_node_full(
         content, "Memory", "soul:boot_count",
         el_from_float(0.9), el_from_float(0.9), el_from_float(1.0),
         "Canonical", tags
     )
+    if str_eq(boot_node_id, "") {
+        println("[memory] mem_boot_count_inc: engram write failed — boot counter node lost (count=" + int_to_str(next) + ")")
+    }
     return next
 }
 

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 + "\"}"
 }

soul.el

@@ -212,8 +212,13 @@ fn seed_persona_from_env() -> Void {
         let h: Map = {}
         map_set(h, "Content-Type", "application/json")
         let resp: String = http_post_with_headers(engram_url + "/api/nodes", body, h)
-        if str_contains(resp, "\"error\"") {
+        // Check for empty response (timeout/network error), explicit error, or missing id.
+        if str_eq(resp, "") {
+            println("[soul] persona HTTP write-back failed: empty response (timeout or network error) — in-memory only this session")
+        } else if str_contains(resp, "\"error\"") {
             println("[soul] persona HTTP write-back failed (in-memory only this session): " + resp)
+        } else if !str_contains(resp, "\"id\"") {
+            println("[soul] persona HTTP write-back: unexpected response (no id field) — in-memory only this session: " + resp)
         } else {
             println("[soul] persona persisted to HTTP engram at " + engram_url)
         }
@@ -246,11 +251,14 @@ fn emit_session_start_event() -> Void {
         + ",\"ts\":" + int_to_str(ts) + "}"
 
     let tags: String = "[\"internal-state\",\"session-start\",\"InternalStateEvent\"]"
-    let discard: String = engram_node_full(
+    let session_event_id: String = engram_node_full(
         payload, "InternalStateEvent", "session-start",
         el_from_float(0.9), el_from_float(0.9), el_from_float(1.0),
         "Episodic", tags
     )
+    if str_eq(session_event_id, "") {
+        println("[soul] emit_session_start_event: engram write failed — session-start event lost")
+    }
     println("[soul] session-start event logged (boot=" + boot_num + " nodes=" + int_to_str(node_ct) + " edges=" + int_to_str(edge_ct) + ")")
 }