When a kanban worker subprocess exits rc=0 but its task is still in
status='running', the agent almost certainly answered the task
conversationally without calling kanban_complete or kanban_block. The
dispatcher used to classify this as a generic crash and respawn, which
loops forever on small local models (gemma4-e2b q4 etc.) that keep
returning clean but unproductive output.
Dispatcher changes:
- The waitpid reap loop at the top of dispatch_once now records each
reaped child's raw exit status in a bounded module registry
(_recent_worker_exits, TTL 600s, size cap 4096).
- _classify_worker_exit distinguishes clean_exit / nonzero_exit /
signaled / unknown using os.WIFEXITED / WIFSIGNALED.
- detect_crashed_workers consults the classification when a worker
is found dead. clean_exit → protocol_violation event + immediate
circuit-breaker trip (failure_limit=1). Everything else keeps the
existing crashed-event + counter behavior.
- DispatchResult.auto_blocked now includes protocol-violation trips.
Gateway fix (Bug A in #20894):
- gateway.run._notify_active_sessions_of_shutdown snapshots
self.adapters with list(...) before iterating. adapter.send() can
hit a fatal-error path that pops the adapter from the dict, which
was raising 'RuntimeError: dictionary changed size during iteration'
during shutdown.
Regression tests:
- test_detect_crashed_workers_protocol_violation_auto_blocks verifies
rc=0 + still-running → status=blocked on first occurrence with
protocol_violation + gave_up events and NO crashed event.
- test_detect_crashed_workers_nonzero_exit_uses_default_limit verifies
non-zero exits keep the existing 2-strike behavior.
Closes#20894.
fdb9e0f6a6