Two real concerns from the code review on ab07297..b266623:
1. ActiveSpeaker removal poisoned the rename-window heuristic. ParticipantTracker.HandleRemoved appends to _recentlyRemoved keyed by MachineName alone; the next Participant Add on the same machine consulted that list with no kind discrimination, so an active-speaker disappearance immediately followed by a participant joining (very common: Teams renames its outputs as participants enter/leave) would cause the new participant to inherit the auto-mix's deterministic v5 GUID. New HandleAutoMixRemoved deliberately skips _recentlyRemoved — the auto-mix row's identity is already stable via the deterministic Id, so re-add restores it without the rename window.
2. IsoPipeline.State writes were not synchronized. Supervisor loop sets State on its own thread; UI thread reads from GetStats. Without volatility, the JIT could cache the field in a register and the UI would stay stuck on Receiving even after Error. Backing field is now an int read/written via Volatile.Read/Volatile.Write, matching the pattern already used for _liveReceiver / _liveSender / _liveProcessor.
Tests: 79/79 (was 78) — added ParticipantTrackerTests.ActiveSpeakerRemove_DoesNotPoisonRenameWindowForLaterParticipant which would have caught (1).
ParticipantTracker now accepts NdiSourceKind.ActiveSpeaker (Teams' auto-mix output — legacy 'MACHINE (Teams)' or current 'MACHINE (MS Teams - Active Speaker)') and surfaces it as a synthetic row in the participant list with the display name 'Active Speaker'. The operator can route it to its own normalized ISO via the same toggle every other participant uses, so vMix / OBS / Ross can subscribe to a single clean active-speaker feed.
Stable Id: derived from SHA1 of 'auto-mix:<machine>' formatted as a v5 GUID, so a discovery cycle that re-adds the source doesn't duplicate the row and the operator's ISO assignment stays bound across the rename window.
Tests: 78/78 unit (was 76) — added ParticipantTrackerTests.ActiveSpeaker_AppearsAsSyntheticAutoMixParticipant + ActiveSpeaker_ReAddOnSameMachine_PreservesId. Existing NonParticipantSources_AreIgnored still passes (only ActiveSpeaker is opted in; ScreenShare and Audio are still ignored).
