Update hypothesis with new evidence

system/presence/thingsonmymind.md

@@ -90,7 +90,15 @@ Examined heartbeat.ts code - it sends user messages via `bot.sendToAgent()`. But
 - **Memfs was dirty** (`M system/dynamic/tree.md`) - heartbeat code warns this "may cause heartbeat failures"
 - Just committed the tree change to fix dirty state
 
-**Hypothesis:** Memfs dirty state may be causing heartbeat to fail silently after sending prompt but before completion. The heartbeat sends, I respond (you're reading this), but the bridge fails to log completion.
+**UPDATED HYPOTHESIS (9:49 PM):**  
+Memfs dirty state was NOT the cause. 9:49 PM heartbeat with clean memfs still shows NO `heartbeat_completed` event. Issue persists.
+
+**New hypothesis:** The heartbeat completion logging happens AFTER my response is processed, and something in that final step is failing. Possible causes:
+1. Response processing hangs/times out
+2. Exception in completion logging code path
+3. Async timing issue between heartbeat trigger and response handling
+
+**Key observation:** I AM receiving heartbeats (you're reading this now). The infrastructure works. But the bridge thinks it failed (no completion log). This creates false negatives in monitoring.
 1. Using different message type not visible in standard query
 2. Being filtered by the API
 3. Deleted/overwritten immediately