Collapse duplicate same-track streaming loads to enforce one load per play

A second LoadTrackStreaming for the same in-flight track (UI double-fire, queue re-entry, or JS false-end auto-advance) is now dropped; a different-track load still supersedes. Targets the Opus double-load; keeps load-gen diagnostics.

DeepDrftPublic.Client/Services/StreamingAudioPlayerService.cs

@@ -53,6 +53,16 @@ public class StreamingAudioPlayerService : AudioPlayerService, IStreamingPlayerS
     private readonly ILogger<StreamingAudioPlayerService> _logger;
     private string? _currentTrackId;
 
+    // The track key of the load currently in flight, set at LoadTrackStreaming entry BEFORE ResetToIdle
+    // (which clears _currentTrackId) and cleared only when that load's finally runs as the still-active
+    // operation. It is the idempotency key that collapses a duplicate same-track entry for ONE play
+    // action into the first load: a second SelectTrackStreaming for the SAME track while its load is
+    // still in flight is a redundant re-dispatch (UI double-fire, queue re-entry, or a JS false-end
+    // auto-advance back onto the same track), not a real track switch, so it is dropped. A load for a
+    // DIFFERENT track is a genuine switch and supersedes as before — this guard never suppresses it.
+    // Null when no load is in flight.
+    private string? _loadInFlightTrackId;
+
     // Monotonic load-generation counter (diagnostic). Incremented on every LoadTrackStreaming entry and
     // stamped into the load's logs so two loads for ONE user play action — the "Duration set from header
     // logged twice" double-load hypothesis that needs in-browser confirmation — are unmistakable: a
@@ -165,12 +175,29 @@ public class StreamingAudioPlayerService : AudioPlayerService, IStreamingPlayerS
 
     private async Task LoadTrackStreaming(TrackDto track)
     {
+        // Idempotency guard (single-load invariant). A load already in flight for THIS SAME track means
+        // a duplicate dispatch of one play action — a UI double-fire, a queue re-entry, or a JS false-end
+        // that auto-advanced back onto the same track. Dropping it collapses the play to exactly one load
+        // without touching the live operation. A load for a DIFFERENT track is a real switch and falls
+        // through to supersede the in-flight one exactly as before, so this never blocks navigation. The
+        // check is on the WASM single-threaded dispatcher, so reading/writing _loadInFlightTrackId needs
+        // no lock; the field is set below before the first await and cleared in finally for the active load.
+        if (_loadInFlightTrackId is { } inFlight && inFlight == track.EntryKey)
+        {
+            _logger.LogInformation(
+                "Streaming load for track {TrackId} skipped — a load for the same track is already in flight (single-load guard)",
+                track.EntryKey);
+            return;
+        }
+        _loadInFlightTrackId = track.EntryKey;
+
         // Always reset to clean state before loading new track. ResetToIdle
         // both cancels and awaits any in-flight streaming loop, so by the time
         // we return from it the previous loop is guaranteed to have exited and
         // there is no risk of interleaved ProcessStreamingChunk calls against
-        // the single-instance JS StreamDecoder.
-        await ResetToIdle();
+        // the single-instance JS StreamDecoder. clearLoadGuard:false — we just armed
+        // _loadInFlightTrackId for THIS load; the prologue reset must not wipe it.
+        await ResetToIdle(clearLoadGuard: false);
 
         // Stamp this load with a fresh generation id (diagnostic — see _loadGeneration). Logged at
         // start and finish so a double-load shows as two overlapping start/finish pairs for one play.
@@ -330,10 +357,17 @@ public class StreamingAudioPlayerService : AudioPlayerService, IStreamingPlayerS
             IsLoading = false;
             _logger.LogInformation("Streaming load #{Gen} finished for track {TrackId} (superseded={Superseded})",
                 loadGeneration, track.EntryKey, !ReferenceEquals(_streamingCancellation, loadCts));
-            // Only notify if this load is still the active operation. A superseding seek
-            // owns state notifications; firing here mid-seek would push a stale snapshot.
+            // Release the single-load guard only when this load is still the active operation. A
+            // superseding load for a DIFFERENT track has already overwritten _loadInFlightTrackId with
+            // its own key before its first await; clearing it here would unlatch the guard mid-way
+            // through that newer load and let a duplicate of IT slip through. The CTS identity is the
+            // same "am I still the active operation?" test the notify/state guards use. ResetToIdle
+            // (the supersede path) does not touch this field — the incoming load owns its lifecycle.
             if (ReferenceEquals(_streamingCancellation, loadCts))
             {
+                _loadInFlightTrackId = null;
+                // Only notify if this load is still the active operation. A superseding seek
+                // owns state notifications; firing here mid-seek would push a stale snapshot.
                 await NotifyStateChanged();
             }
         }
@@ -935,9 +969,15 @@ public class StreamingAudioPlayerService : AudioPlayerService, IStreamingPlayerS
     }
 
     /// <summary>
-    /// Single method to reset all state - called by both Stop and Unload.
+    /// Single method to reset all state - called by both Stop and Unload, and as the prologue of a new
+    /// load. <paramref name="clearLoadGuard"/> is true for the direct stop/unload/dispose callers and
+    /// false when a fresh <see cref="LoadTrackStreaming"/> calls it: that load has already set
+    /// <c>_loadInFlightTrackId</c> to its own key to arm the single-load guard, so the prologue must not
+    /// wipe it. The direct callers DO clear it so a later replay of the same track is not wrongly
+    /// suppressed by a guard key left over from an interrupted in-flight load (whose CTS-identity check
+    /// in finally fails after ResetToIdle nulls the CTS, so the load itself never clears the field).
     /// </summary>
-    private async Task ResetToIdle()
+    private async Task ResetToIdle(bool clearLoadGuard = true)
     {
         // 0. Close any open play session BEFORE tearing down (§2.1). ResetToIdle is the single funnel
         //    for stop / unload / dispose / track-switch (a new LoadTrackStreaming calls it first), so a
@@ -987,6 +1027,12 @@ public class StreamingAudioPlayerService : AudioPlayerService, IStreamingPlayerS
         _currentTrackId = null;
         _currentFormat = AudioFormat.Lossless;
 
+        // Direct stop/unload/dispose: release the single-load guard so a later replay of the same track
+        // is not suppressed. NOT cleared on the load prologue (clearLoadGuard:false) — that load owns the
+        // key it just armed.
+        if (clearLoadGuard)
+            _loadInFlightTrackId = null;
+
         await NotifyStateChanged();
     }