Status fields (_lastDrainUtc, _lastSuccessUtc, _lastError, _drainState,
_evictedCount) were written by the drain timer thread and read by
GetStatus() / health-check threads with no memory barrier, risking torn
DateTime? reads and stale DrainState observations.
- Added _statusLock object; all writes to status fields now happen inside
lock(_statusLock) blocks in DrainOnceAsync and DrainTimerCallback.
- GetStatus() snapshots all fields atomically under the same lock so the
Admin UI / /healthz endpoint always sees a consistent view.
- Regression test GetStatus_snapshot_is_consistent_under_concurrent_drain
drives status writes and reads from concurrent threads; asserts no throws.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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