_handle_polling_network_error's chained retry never updated
self._polling_error_task, so the reentrancy guard shared with the
heartbeat loop and the pending-updates probe went stale mid-recovery,
letting more than one recovery attempt run concurrently against the
same adapter. Combined with a TOCTOU window in
_handle_adapter_fatal_error (the adapter was only removed from
self.adapters in a finally block after awaiting disconnect()), two
concurrent fatal notifications for the same adapter could both pass
the "still installed" check and call disconnect() twice, which is
where the reported "'NoneType' object has no attribute 'updater'"
originates once self._app is cleared by the first call.
- Reassign the chained retry task to self._polling_error_task so the
guard reflects an in-flight recovery.
- Capture self._app in a local variable across the stop/start_polling
sequence instead of re-reading self._app between awaits.
- Claim (pop) the adapter from self.adapters before awaiting
disconnect() in _handle_adapter_fatal_error, not after, closing the
TOCTOU window for a concurrent notification on the same adapter.
a682091044