- Wrap child.run_conversation() in a ThreadPoolExecutor with configurable
timeout (delegation.child_timeout_seconds, default 300s) to prevent
indefinite blocking when a subagent's API call or tool HTTP request hangs.
- Add heartbeat stale detection: if a child's api_call_count doesn't
advance for 5 consecutive heartbeat cycles (~2.5 min), stop touching
the parent's activity timestamp so the gateway inactivity timeout
can fire as a last resort.
- Add 'timeout' as a new exit_reason/status alongside the existing
completed/max_iterations/interrupted states.
- Use shutdown(wait=False) on the timeout executor to avoid the
ThreadPoolExecutor.__exit__ deadlock when a child is stuck on
blocking I/O.
Closes#13768
dd8ab40556