Fix iTunes album tracks failing on region-restricted releases

iTunes API can return collection metadata without song tracks for
region-restricted albums. The _lookup fallback only checked if results
was empty, so a collection-only response was accepted and cached as
{'items': []}. All future lookups returned the cached empty result.

Three fixes:
- get_album_tracks now checks for actual song items and tries fallback
  storefronts when only collection metadata is returned
- Skip cached results with empty items array (prevents stale cache hits)
- Backend returns descriptive 404 error, frontend surfaces it in toast

core/itunes_client.py

@@ -735,7 +735,7 @@ class iTunesClient:
         # Check cache for album tracks listing
         cache = get_metadata_cache()
         cached = cache.get_entity('itunes', 'album', f"{album_id}_tracks")
-        if cached:
+        if cached and cached.get('items'):
             return cached
 
         results = self._lookup(id=album_id, entity='song')
@@ -743,6 +743,39 @@ class iTunesClient:
         if not results:
             return None
 
+        # Check if results contain actual song tracks (not just collection metadata).
+        # iTunes sometimes returns only the collection/album info without songs
+        # (region-restricted tracks). The _lookup fallback only checks if results
+        # is empty, so a collection-only response bypasses fallback storefronts.
+        has_songs = any(
+            item.get('wrapperType') == 'track' and item.get('kind') == 'song'
+            for item in results
+        )
+        if not has_songs:
+            # Try fallback storefronts for actual song tracks
+            logger.info(f"Album {album_id} returned collection info but no songs, trying fallback storefronts")
+            for fallback in self.FALLBACK_COUNTRIES:
+                if fallback == self.country:
+                    continue
+                try:
+                    fb_results = self.session.get(
+                        self.LOOKUP_URL,
+                        params={'id': album_id, 'entity': 'song', 'country': fallback},
+                        timeout=15
+                    )
+                    if fb_results.status_code == 200:
+                        fb_data = fb_results.json().get('results', [])
+                        if any(i.get('wrapperType') == 'track' and i.get('kind') == 'song' for i in fb_data):
+                            logger.info(f"Found song tracks via fallback storefront: {fallback}")
+                            results = fb_data
+                            has_songs = True
+                            break
+                except Exception:
+                    continue
+            if not has_songs:
+                logger.warning(f"Album {album_id} has no song tracks in any storefront")
+                return None
+
         # First result is usually the album/collection info
         # Extract album information to include in each track (like Spotify does)
         album_info = None

web_server.py

@@ -11653,8 +11653,8 @@ def get_artist_album_tracks(artist_id, album_id):
 
         # Get album tracks
         tracks_data = client.get_album_tracks(resolved_album_id)
-        if not tracks_data or 'items' not in tracks_data:
-            return jsonify({"error": "No tracks found for album"}), 404
+        if not tracks_data or 'items' not in tracks_data or len(tracks_data['items']) == 0:
+            return jsonify({"error": "No tracks found for album — it may be region-restricted or unavailable on this metadata source"}), 404
         
         # Handle both dict and object responses from spotify_client.get_album()
         if isinstance(album_data, dict):

webui/static/script.js

@@ -37520,7 +37520,8 @@ async function createArtistAlbumVirtualPlaylist(album, albumType) {
             if (response.status === 401) {
                 throw new Error('Spotify not authenticated. Please check your API settings.');
             }
-            throw new Error(`Failed to load album tracks: ${response.status}`);
+            const errData = await response.json().catch(() => ({}));
+            throw new Error(errData.error || `Failed to load album tracks: ${response.status}`);
         }
 
         const data = await response.json();