fix(scanner): defer artwork PreCache calls until after transaction commits

The CacheWarmer was failing with data not found errors because PreCache was being called inside the database transaction before the data was committed. The CacheWarmer runs in a separate goroutine with its own database context and could not access the uncommitted data due to transaction isolation.

Changed the persistChanges method in phase_1_folders.go to collect artwork IDs during the transaction and only call PreCache after the transaction successfully commits. This ensures the artwork data is visible to the CacheWarmer when it attempts to retrieve and cache the images.

The fix eliminates the data not found errors and allows the cache warmer to properly pre-cache album and artist artwork during library scanning.

Signed-off-by: Deluan <deluan@navidrome.org>

scanner/phase_1_folders.go

@@ -324,6 +324,9 @@ func (p *phaseFolders) persistChanges(entry *folderEntry) (*folderEntry, error)
 	defer p.measure(entry)()
 	p.state.changesDetected.Store(true)
 
+	// Collect artwork IDs to pre-cache after the transaction commits
+	var artworkIDs []model.ArtworkID
+
 	err := p.ds.WithTx(func(tx model.DataStore) error {
 		// Instantiate all repositories just once per folder
 		folderRepo := tx.Folder(p.ctx)
@@ -362,7 +365,7 @@ func (p *phaseFolders) persistChanges(entry *folderEntry) (*folderEntry, error)
 				return err
 			}
 			if entry.artists[i].Name != consts.UnknownArtist && entry.artists[i].Name != consts.VariousArtists {
-				entry.job.cw.PreCache(entry.artists[i].CoverArtID())
+				artworkIDs = append(artworkIDs, entry.artists[i].CoverArtID())
 			}
 		}
 
@@ -374,7 +377,7 @@ func (p *phaseFolders) persistChanges(entry *folderEntry) (*folderEntry, error)
 				return err
 			}
 			if entry.albums[i].Name != consts.UnknownAlbum {
-				entry.job.cw.PreCache(entry.albums[i].CoverArtID())
+				artworkIDs = append(artworkIDs, entry.albums[i].CoverArtID())
 			}
 		}
 
@@ -411,6 +414,14 @@ func (p *phaseFolders) persistChanges(entry *folderEntry) (*folderEntry, error)
 	if err != nil {
 		log.Error(p.ctx, "Scanner: Error persisting changes to DB", "folder", entry.path, err)
 	}
+
+	// Pre-cache artwork after the transaction commits successfully
+	if err == nil {
+		for _, artID := range artworkIDs {
+			entry.job.cw.PreCache(artID)
+		}
+	}
+
 	return entry, err
 }