When handleAgentEnd dispatches a sub-unit (via hooks, triage, or quick-task
early-dispatch paths) and that unit completes before handleAgentEnd returns,
the resulting agent_end event is silently dropped by the reentrancy guard.
This leaves auto-mode active but permanently stalled — no unit running, no
watchdog set, process at high CPU doing nothing.
Add a pendingAgentEndRetry flag to AutoSession that the reentrancy guard sets
when it drops an agent_end event. The finally block in handleAgentEnd checks
this flag and schedules a deferred retry via setImmediate, ensuring the
completed unit's agent_end is always processed.
b2befe3628