H13: _devices/_devicesByRoutingKey are published by reference swap under a
lifecycle lock and never mutated after publish, so the retained poll engine,
discovery and the actor's GetHostStatuses pull never read a table mid-Clear.
Every retire (init's own release, shutdown, dispose) takes the table it
replaces, so ShutdownAsync racing DisposeAsync tears each state down once, and
a generation check makes an InitializeAsync overtaken by a shutdown publish
nothing (it throws OperationCanceledException) instead of resurrecting probe
loops behind the shutdown. Probe join is one bounded 5 s wait independent of
the caller token.
H21: _health is volatile and read-modify-write updates go through a CAS.
F10: the sync Dispose() (sync-over-async) is removed; DisposeAsync is the
complete, idempotent teardown the runtime calls after ShutdownAsync.
Refs #737
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty
20cb2a52d6