The observe tests raced a background thread (5 ms wall-clock sleep)
against the coordinator reaching its resubscribe. try_enter_observe_mode
clears _notified before subscribing, so a notify only counts if it lands
between that clear and the end of the grace sleep. When the intervening
update cycle (reconnect, cache sweep, executor hops) took longer than
5 ms, every notify was cleared and the mode stayed 'poll' —
test_reconnect_from_observe_mode_resubscribes_immediately failed roughly
1 in 7 runs.
Replace the threads with FakeObserveSession.notify_on_subscribe, which
delivers the rep synchronously from subscribe() the way a real device
answers a subscription. That puts the notify inside the grace window by
construction rather than by timing. Tests that require the resubscribe to
fail now set it to None explicitly instead of relying on the absence of a
racing thread.
No production code changed; no assertion weakened, and no sleeps, retries
or timeouts added.
Claude-Session: https://claude.ai/code/session_01PUSU6tDjHjtbExtyXDPT3N
Tim Schindler
0715eb0829