perf: optimize system concurrency, I/O stability and fix WebSocket disconnects

backend/core/state_sync.py

@@ -123,7 +123,11 @@ class StateSync:
         # Persist to feed_history
         if persist:
             self.storage.add_feed_message(self._state, event)
-            self.save_state()
+            # Make persistence non-blocking to keep event loop snappy
+            if asyncio.get_event_loop().is_running():
+                asyncio.create_task(asyncio.to_thread(self.save_state))
+            else:
+                self.save_state()
 
         # Broadcast to frontend
         if self._broadcast_fn: