fix(audio): guard underrun/stream-complete against false end-of-playback

pause() clears underrun_ so setStreamComplete can't fire TrackEnded while paused; resetToStart() resets streamComplete. Prior fix: underrun_ park + streamComplete discriminator prevent the Opus-startup false-end. Tests: 18 PlaybackScheduler cases including pause-during-underrun and underrun->resume->genuine-end-once.

DeepDrftPublic.Client/Services/AudioPlayerService.cs

@@ -186,6 +186,10 @@ public abstract class AudioPlayerService : IPlayerService, IAsyncDisposable
             var result = await _audioInterop.UnloadAsync(PlayerId);
             if (result.Success)
             {
+                // [RELOAD-DIAG] One of two base-class sites that null Duration (the other is
+                // OnPlaybackEndCallback). Logged so a run can attribute a "Duration set from header"
+                // re-fire to this path vs the spurious end-callback. Trivially removable.
+                OnDurationNulledDiag("Unload");
                 IsPlaying = false;
                 IsPaused = false;
                 CurrentTime = 0;
@@ -278,6 +282,12 @@ public abstract class AudioPlayerService : IPlayerService, IAsyncDisposable
 
     private async Task OnPlaybackEndCallback()
     {
+        // [RELOAD-DIAG] The second base-class Duration-null site — the JS PlaybackScheduler's
+        // end-of-playback callback. A false (mid-stream) fire here is the Opus-startup bug: it nulls
+        // Duration (forcing a second "Duration set from header"), sets IsLoaded=false/CurrentTime=0,
+        // and raises TrackEnded (premature queue auto-advance). After the scheduler fix this must fire
+        // only on genuine end-of-track. Trivially removable.
+        OnDurationNulledDiag("OnPlaybackEndCallback");
         IsPlaying = false;
         IsPaused = false;
         IsLoaded = false;
@@ -308,6 +318,14 @@ public abstract class AudioPlayerService : IPlayerService, IAsyncDisposable
     /// </summary>
     protected virtual void OnPlaybackEnded() { }
 
+    /// <summary>
+    /// [RELOAD-DIAG] Diagnostic seam — invoked at each base-class site that nulls <see cref="Duration"/>
+    /// (<see cref="Unload"/> and <see cref="OnPlaybackEndCallback"/>), naming the caller. The streaming
+    /// subclass overrides this to emit a tagged log via its logger so a run can attribute a re-fired
+    /// "Duration set from header" to its true cause. No-op in the base; trivially removable.
+    /// </summary>
+    protected virtual void OnDurationNulledDiag(string caller) { }
+
 
     protected async Task EnsureInitializedAsync()
     {

DeepDrftPublic.Client/Services/StreamingAudioPlayerService.cs

@@ -138,6 +138,12 @@ public class StreamingAudioPlayerService : AudioPlayerService, IStreamingPlayerS
     // Organic end-of-stream closes the session; the bucket reflects the high-water fraction reached.
     protected override void OnPlaybackEnded() => _playTracker?.Close();
 
+    // [RELOAD-DIAG] Emit the tagged log at each base-class Duration-null site so a run unambiguously
+    // shows which path nulled Duration between two "Duration set from header" lines. Trivially removable.
+    protected override void OnDurationNulledDiag(string caller) =>
+        _logger.LogInformation(
+            "[RELOAD-DIAG] Base nulling Duration caller={Caller} (gen={Gen})", caller, _loadGeneration);
+
     public override async Task SelectTrack(TrackDto track)
     {
         await SelectTrackStreaming(track);