fix(chat): fix auto_persist timestamp extraction and bell label uniqueness

- engram_compile: BellEvent nodes do not carry created_at in the engram
  node JSON; extract the unix timestamp from the embedded ' | ts:NNNNN'
  pattern in the content string instead. Fall back to created_at/updated_at
  if the marker is absent. Guard str_to_int against empty string so the 72h
  recency check never silently treats every node as epoch-0 stale.

- auto_persist: append the current unix timestamp to the BellEvent label
  ('bell:soft:1749876543') to make it unique per turn. The previous label
  ('bell:soft') was the same for every soft bell, causing engram to treat
  all subsequent writes as updates to the same node.

chat.el

@@ -53,8 +53,22 @@ fn engram_compile(intent: String) -> String {
     let cutoff_ts: Int = now_ts - 259200
     let recent_bell: String = if bell_ok {
         let bn0: String = json_array_get(bell_nodes, 0)
-        let bn_ts_raw: String = json_get(bn0, "created_at")
-        let bn_ts: Int = str_to_int(bn_ts_raw)
+        // created_at is not present in engram node JSON for BellEvent nodes.
+        // Extract the timestamp embedded in the content string as " | ts:NNNNN".
+        // Fall back to created_at / updated_at JSON fields if the marker is absent.
+        let bn_content: String = json_get(bn0, "content")
+        let ts_marker: String = " | ts:"
+        let ts_pos: Int = str_index_of(bn_content, ts_marker)
+        let bn_ts_raw: String = if ts_pos >= 0 {
+            let ts_start: Int = ts_pos + str_len(ts_marker)
+            let rest: String = str_slice(bn_content, ts_start, str_len(bn_content))
+            let next_sep: Int = str_index_of(rest, " | ")
+            if next_sep < 0 { rest } else { str_slice(rest, 0, next_sep) }
+        } else {
+            let ca: String = json_get(bn0, "created_at")
+            if str_eq(ca, "") { json_get(bn0, "updated_at") } else { ca }
+        }
+        let bn_ts: Int = if str_eq(bn_ts_raw, "") { 0 } else { str_to_int(bn_ts_raw) }
         if bn_ts > cutoff_ts { bn0 } else { "" }
     } else { "" }
     let affective_part: String = if !str_eq(recent_bell, "") { recent_bell } else { "" }
@@ -1270,10 +1284,12 @@ fn auto_persist(req: String, resp: String) -> Void {
         let sal_c: String = if str_eq(bell_level, "hard") { el_from_float(1.0) } else { el_from_float(0.95) }
 
         let bell_tags: String = "[\"safety\",\"bell\",\"bell:" + bell_level + "\",\"affective\",\"BellEvent\"]"
+        let bell_ts_str: String = int_to_str(time_now())
+        let bell_label: String = "bell:" + bell_level + ":" + bell_ts_str
         let bell_node_id: String = engram_node_full(
             bell_content,
             "BellEvent",
-            "bell:" + bell_level,
+            bell_label,
             sal_a,
             sal_b,
             sal_c,