PerPlatformProbeWatcher records a platform's handle and publishes the probe
binding into the driver registry as one step under _syncLock, but
WatchedPlatforms read the handle map lock-free - so it could report a
platform one step ahead of the registry Upsert. A ScanState event raised in
that window was dispatched by the EventPump, missed ResolveSubscribers and
was dropped as "stale after unsubscribe", leaving the host status empty.
That is the #856 flake: A_fetch_completing_after_init_populates_host_statuses
waited for WatchedPlatforms, emitted ScanState, and timed out at 10 s on the
final Running wait. Reproduced 11/700 (28 parallel runners x 25 + 14 CPU
burners), every failure at that step with the binding present by the time of
diagnosis and hostStatuses=[] - i.e. the event was dropped. 0/1400 after.
WatchedPlatforms now reads under _syncLock (test seam only; the dispatch path
already checks the map after the registry, the safe order). New
PerPlatformProbeWatcherVisibilityTests spins a reader on another thread and
asserts the registry entry exists the moment the platform is visible
(old code: torn in 1691/2000 iterations). WaitUntilAsync gains a describe
overload; the #856 test's waits now report elapsed time and the observed
seed/binding/pump/host-status chain on timeout.
Claude-Session: https://claude.ai/code/session_01GT67AD99zQQqpLCVm3p7xk
Joseph Doherty
988046cbe4