fix: use ID3v2 '/' separator for multi-artist tracks (Plex compatible)

Multi-artist tracks were using comma separator which Plex interprets as a
single artist name. Changed to '/' separator (ID3v2.4 standard) which Plex
and other media servers recognize for multi-artist tracks.

- Updated all artist joining to use '/' instead of ', '
- Added _split_multi_artist() to properly write multiple artist tag values
- ID3 (MP3): writes multiple values in TPE1 frame
- Vorbis (FLAC/OGG): writes multiple artist fields
- MP4 (M4A): writes multiple artist values

Affected files:
- web_server.py: _join_artist_names() and metadata assembly
- core/tag_writer.py: ID3/Vorbis/MP4 writer functions
- core/personalized_playlists.py: track artist joining
- core/seasonal_discovery.py: album artist joining
- core/hifi_client.py: track artist parsing

core/hifi_client.py

@@ -303,7 +303,8 @@ class HiFiClient:
                     names.append(a.get('name', ''))
                 elif isinstance(a, str):
                     names.append(a)
-            artist_name = ', '.join(n for n in names if n) or 'Unknown Artist'
+            # Use "/" as separator for multi-artist tracks (ID3v2 standard, recognized by Plex)
+            artist_name = '/'.join(n for n in names if n) or 'Unknown Artist'
         elif isinstance(artists_raw, dict):
             artist_name = artists_raw.get('name', 'Unknown Artist')
         elif isinstance(artists_raw, str):

core/personalized_playlists.py

@@ -991,7 +991,7 @@ class PersonalizedPlaylistsService:
                                     all_tracks.append({
                                         'spotify_track_id': track['id'],
                                         'track_name': track['name'],
-                                        'artist_name': ', '.join([a['name'] for a in track.get('artists', [])]),
+                                        'artist_name': '/'.join([a['name'] for a in track.get('artists', [])]),
                                         'album_name': album_data.get('name', 'Unknown'),
                                         'album_cover_url': album_data.get('images', [{}])[0].get('url') if album_data.get('images') else None,
                                         'duration_ms': track.get('duration_ms', 0),
@@ -1029,7 +1029,7 @@ class PersonalizedPlaylistsService:
                                     all_tracks.append({
                                         'spotify_track_id': track_id,
                                         'track_name': track.get('name', ''),
-                                        'artist_name': ', '.join(artist_names) if artist_names else 'Unknown',
+                                        'artist_name': '/'.join(artist_names) if artist_names else 'Unknown',
                                         'album_name': album_name,
                                         'album_cover_url': album_cover,
                                         'duration_ms': track.get('duration_ms', 0),

core/seasonal_discovery.py

@@ -537,7 +537,7 @@ class SeasonalDiscoveryService:
                             seasonal_albums.append({
                                 'spotify_album_id': album.id,
                                 'album_name': album.name,
-                                'artist_name': ', '.join(album.artists) if album.artists else 'Various Artists',
+                                'artist_name': '/'.join(album.artists) if album.artists else 'Various Artists',
                                 'album_cover_url': album.image_url if hasattr(album, 'image_url') else None,
                                 'release_date': album.release_date if hasattr(album, 'release_date') else None,
                                 'popularity': getattr(album, 'popularity', 50)
@@ -567,7 +567,7 @@ class SeasonalDiscoveryService:
                             seasonal_albums.append({
                                 'spotify_album_id': album.id,  # Column name is spotify_album_id but stores iTunes ID too
                                 'album_name': album.name,
-                                'artist_name': ', '.join(album.artists) if album.artists else 'Various Artists',
+                                'artist_name': '/'.join(album.artists) if album.artists else 'Various Artists',
                                 'album_cover_url': album.image_url if hasattr(album, 'image_url') else None,
                                 'release_date': album.release_date if hasattr(album, 'release_date') else None,
                                 'popularity': 50  # iTunes has no popularity — default mid-range

core/tag_writer.py

@@ -305,7 +305,8 @@ def _write_id3(audio, title, artist, album_artist, album, year, genre,
         written.append('title')
     if artist:
         audio.tags.delall('TPE1')
-        audio.tags.add(TPE1(encoding=3, text=[artist]))
+        artists = _split_multi_artist(artist)
+        audio.tags.add(TPE1(encoding=3, text=artists))
         written.append('artist')
     if album_artist:
         audio.tags.delall('TPE2')
@@ -346,7 +347,8 @@ def _write_vorbis(audio, title, artist, album_artist, album, year, genre,
         audio['title'] = [title]
         written.append('title')
     if artist:
-        audio['artist'] = [artist]
+        artists = _split_multi_artist(artist)
+        audio['artist'] = artists
         written.append('artist')
     if album_artist:
         audio['albumartist'] = [album_artist]
@@ -380,7 +382,8 @@ def _write_mp4(audio, title, artist, album_artist, album, year, genre,
         audio['\xa9nam'] = [title]
         written.append('title')
     if artist:
-        audio['\xa9ART'] = [artist]
+        artists = _split_multi_artist(artist)
+        audio['\xa9ART'] = artists
         written.append('artist')
     if album_artist:
         audio['aART'] = [album_artist]
@@ -477,6 +480,19 @@ def _parse_track_num(val) -> Optional[int]:
         return None
 
 
+def _split_multi_artist(artist_str: str) -> List[str]:
+    """Split a multi-artist string into individual artist names.
+    
+    Handles the '/' separator used by ID3v2.4 for multi-artist tracks.
+    Returns a list of individual artist names.
+    """
+    if not artist_str:
+        return []
+    if '/' in artist_str:
+        return [a.strip() for a in artist_str.split('/') if a.strip()]
+    return [artist_str]
+
+
 def _normalize_for_compare(val) -> str:
     """Normalize a value for comparison."""
     if val is None:

web_server.py

@@ -18035,8 +18035,11 @@ def _extract_spotify_metadata(context: dict, artist: dict, album_info: dict) ->
                 all_artists.append(a)
             else:
                 all_artists.append(str(a))
-        metadata['artist'] = ', '.join(all_artists)
-        print(f"Metadata: Using all artists: '{metadata['artist']}'")
+# Use "/" as separator for multi-artist tracks (ID3v2 standard, recognized by Plex)
+        # This allows Plex to properly identify individual artists instead of treating
+        # "Artist A, Artist B" as a single artist name
+        metadata['artist'] = '/'.join(all_artists)
+        print(f"🎵 Metadata: Using all artists: '{metadata['artist']}'")
     else:
         # Fallback to single artist
         metadata['artist'] = artist.get('name', '')
@@ -33143,8 +33146,9 @@ def _extract_artist_names(artists):
     return [_extract_artist_name(a) for a in (artists or [])]
 
 def _join_artist_names(artists):
-    """Join artist names from a list that may contain dicts or strings."""
-    return ', '.join(_extract_artist_names(artists))
+    """Join artist names from a list that may contain dicts or strings.
+    Uses '/' as separator for multi-artist tracks (ID3v2 standard, recognized by Plex)."""
+    return '/'.join(_extract_artist_names(artists))
 
 def _get_discovery_cache_key(title, artist):
     """Normalize title/artist for discovery cache lookup using matching_engine."""