Fence FFmpeg close cleanup by load generation

src/ui/Logic/VideoPlayers/Ffmpeg/FfmpegPlayer.cs

@@ -205,24 +205,33 @@ public Task LoadFile(string fileName, double startPositionSeconds = 0)
 
     public void CloseFile()
     {
-        Interlocked.Increment(ref _loadGeneration);
+        var generation = Interlocked.Increment(ref _loadGeneration);
         var session = Interlocked.Exchange(ref _session, null);
         _fileName = string.Empty;
         session?.Dispose();
 
+        // Dispose can wait on stubborn workers. If another load became current meanwhile, this
+        // older close must not clear the newer session's decoder badge or presented frame.
+        TryClearOwnerMediaStateForGeneration(generation);
+    }
+
+    internal bool TryClearOwnerMediaStateForGeneration(int loadGeneration)
+    {
         lock (_currentFrameLock)
         {
-            // Any worker that survives the teardown timeout belongs to an older load generation
-            // and may no longer publish UI state after this point.
-            _decoderName = string.Empty;
+            if (loadGeneration != Volatile.Read(ref _loadGeneration))
+            {
+                return false;
+            }
 
-            // The frame belonged to the session's pool, which is gone now.
+            _decoderName = string.Empty;
             _currentFrame?.Dispose();
             _currentFrame = null;
+            Interlocked.Increment(ref _frameVersion);
         }
 
-        Interlocked.Increment(ref _frameVersion);
         FrameReady?.Invoke();
+        return true;
     }
 
     public void Play()

tests/UI/Logic/FfmpegPlayerTests.cs

@@ -247,6 +247,33 @@ public void StaleSessionCannotOverwriteDecoderBadgeAfterClose()
         Assert.Equal("ffmpeg", player.Name);
     }
 
+    [Fact]
+    public void StaleCloseCleanupCannotClearNewerGenerationMediaState()
+    {
+        using var player = new FfmpegPlayer();
+        var queue = new VideoFrameQueue(1);
+        var serial = 0;
+
+        player.CloseFile(); // generation 0 -> 1
+
+        Assert.True(player.TrySetDecoderNameFromSession(1, "current-hardware"));
+        var frame = queue.Rent(4, 4, 0, ref serial)!;
+        Assert.True(player.TryPresentFrameFromSession(1, frame, queue));
+        var currentVersion = player.FrameVersion;
+
+        Assert.False(player.TryClearOwnerMediaStateForGeneration(0));
+        Assert.Contains("current-hardware", player.Name);
+        Assert.Equal((4, 4), player.CurrentFrameSize);
+        Assert.Equal(currentVersion, player.FrameVersion);
+
+        Assert.True(player.TryClearOwnerMediaStateForGeneration(1));
+        Assert.Equal("ffmpeg", player.Name);
+        Assert.Equal((0, 0), player.CurrentFrameSize);
+        Assert.Equal(currentVersion + 1, player.FrameVersion);
+
+        queue.Close();
+    }
+
     [Fact]
     public void StaleSessionFrameIsReturnedInsteadOfPublishedAfterClose()
     {