Fix FlacCacheSink error when reusing cached files

When a file was already in cache, add_from_reader() would return
immediately after reading only 1024 bytes to compute the pk. This
closed the flac_stream and pcm_tx, causing the pump to terminate
normally. However, the dispatcher treated track_tx.send() failure
as a fatal error, even though the pump had completed successfully.

Changes:
- In phase 3 post-prebuffer, when track_tx.send() fails, wait for
  pump to complete and check its result
- If pump returned Ok(), drain remaining segments until TrackBoundary
- If pump returned Err(), propagate the error
- This allows graceful handling of cache hits while preserving error
  detection for genuine pump failures

Fixes the "Pump task died" error when relaunching play_and_cache
with existing cached files.

pmoaudio-ext/src/sinks/flac_cache_sink.rs

@@ -323,9 +323,38 @@ impl NodeLogic for FlacCacheSinkLogic {
                     _AudioSegment::Chunk(_) => {
                         // Continuer à dispatcher vers le pump
                         if track_tx.send(segment).await.is_err() {
-                            // Le pump est mort - erreur
-                            tracing::error!("FlacCacheSink: pump died during post-prebuffer phase");
-                            return Err(AudioError::ProcessingError("Pump task died".to_string()));
+                            // Le pump a fermé son channel - cela peut arriver si le fichier
+                            // était déjà en cache (add_from_reader retourne immédiatement)
+                            tracing::debug!("FlacCacheSink: pump closed track_tx, checking pump status");
+                            drop(track_tx);
+
+                            // Attendre que le pump se termine et vérifier le résultat
+                            match pump_handle.await {
+                                Ok(Ok(_)) => {
+                                    // Le pump s'est terminé proprement (fichier était en cache)
+                                    tracing::debug!("FlacCacheSink: pump completed successfully, draining remaining segments");
+                                    // Drainer les segments restants jusqu'au TrackBoundary
+                                    match drain_until_track_boundary(&mut rx, &stop_token).await? {
+                                        StopReason::TrackBoundary(_) => {
+                                            track_number += 1;
+                                            break; // Continue avec la prochaine track
+                                        }
+                                        StopReason::EndOfStream | StopReason::ChannelClosed => {
+                                            return Ok(());
+                                        }
+                                    }
+                                }
+                                Ok(Err(e)) => {
+                                    // Le pump a rencontré une erreur
+                                    tracing::error!("FlacCacheSink: pump died with error: {}", e);
+                                    return Err(e);
+                                }
+                                Err(e) => {
+                                    // Le pump task a paniqué
+                                    tracing::error!("FlacCacheSink: pump task panicked: {}", e);
+                                    return Err(AudioError::ProcessingError("Pump task panicked".to_string()));
+                                }
+                            }
                         }
                     }
                     _AudioSegment::Sync(marker) => match &**marker {