Phase 21.3: seek-back-past-window refill + clean refill-failure recovery

Seek-back past the retained tail reuses the existing seek-beyond-buffer
Range path (per-path resolver). A failed refill now halts the scheduler
into a paused-but-loaded state (AC6) instead of a silent false end.

DeepDrftPublic.Client/Services/AudioInteropService.cs

@@ -183,6 +183,18 @@ public class AudioInteropService : IAsyncDisposable
         return await InvokeJsAsync<AudioOperationResult>("DeepDrftAudio.reinitializeFromOffset", playerId, totalStreamLength, seekPosition);
     }
 
+    /// <summary>
+    /// Phase 21.3 / AC6 clean-failure recovery: after a window-miss refill (seek-back past the
+    /// retained tail) fails its Range fetch or reinit, halt the starved scheduler and leave the
+    /// player paused-but-loaded at <paramref name="seekPosition"/> so no silent false end fires and a
+    /// retry is possible. Routes through <see cref="InvokeJsAsync{T}"/> so an interop failure during
+    /// recovery still yields a failure result rather than throwing into the seek path.
+    /// </summary>
+    public async Task<AudioOperationResult> RecoverFromFailedRefill(string playerId, double seekPosition)
+    {
+        return await InvokeJsAsync<AudioOperationResult>("DeepDrftAudio.recoverFromFailedRefill", playerId, seekPosition);
+    }
+
     public async Task<AudioOperationResult> SetVolumeAsync(string playerId, double volume)
     {
         return await InvokeJsAsync<AudioOperationResult>("DeepDrftAudio.setVolume", playerId, volume);