Implement runtime agent loop and container hygiene

app/agent/policies.py

@@ -19,9 +19,13 @@ class ChatActivityPolicy:
         self.inactivity_threshold = timedelta(minutes=inactivity_threshold_minutes)
         self.last_message_time: dict[str, datetime] = {}
 
-    def record_activity(self, session_id: str) -> None:
+    def record_activity(self, session_id: str, occurred_at: datetime | None = None) -> None:
         """Record that chat activity occurred."""
-        self.last_message_time[session_id] = datetime.utcnow()
+        self.last_message_time[session_id] = occurred_at or datetime.utcnow()
+
+    def last_activity_at(self, session_id: str) -> datetime | None:
+        """Get the most recent chat activity time for a session."""
+        return self.last_message_time.get(session_id)
 
     def minutes_since_activity(self, session_id: str) -> int:
         """Get minutes since last chat message."""