Fix hero slider + recommended modal returning 0 artists

get_top_similar_artists now accepts require_source parameter to filter
by source ID in SQL. Previously fetched 200 artists then post-filtered,
but cycling logic (last_featured ASC) rotated artists without IDs to
the front, causing all 200 to be filtered out.

Both /api/discover/hero and /api/discover/similar-artists now pass
require_source=active_source so only artists with valid IDs are returned.

database/music_database.py

@@ -7260,13 +7260,23 @@ class MusicDatabase:
             logger.error(f"Error checking similar artists freshness: {e}")
             return False  # Default to re-fetching on error
 
-    def get_top_similar_artists(self, limit: int = 50, profile_id: int = 1) -> List[SimilarArtist]:
+    def get_top_similar_artists(self, limit: int = 50, profile_id: int = 1, require_source: str = None) -> List[SimilarArtist]:
-        """Get top similar artists excluding watchlist artists, with cycling support"""
+        """Get top similar artists excluding watchlist artists, with cycling support.
+        require_source: if set ('spotify','itunes','deezer'), only returns artists with that source ID."""
         try:
             with self._get_connection() as conn:
                 cursor = conn.cursor()
 
-                cursor.execute("""
+                # Build source filter
+                source_filter = ''
+                if require_source == 'spotify':
+                    source_filter = "AND sa.similar_artist_spotify_id IS NOT NULL AND sa.similar_artist_spotify_id != ''"
+                elif require_source == 'itunes':
+                    source_filter = "AND sa.similar_artist_itunes_id IS NOT NULL AND sa.similar_artist_itunes_id != ''"
+                elif require_source == 'deezer':
+                    source_filter = "AND sa.similar_artist_deezer_id IS NOT NULL AND sa.similar_artist_deezer_id != ''"
+
+                cursor.execute(f"""
                     SELECT
                         MAX(sa.id) as id,
                         MAX(sa.source_artist_id) as source_artist_id,
@@ -7287,7 +7297,7 @@ class MusicDatabase:
                         OR (sa.similar_artist_deezer_id IS NOT NULL AND sa.similar_artist_deezer_id = wa.deezer_artist_id)
                         OR LOWER(sa.similar_artist_name) = LOWER(wa.artist_name)
                     ) AND wa.profile_id = ?
-                    WHERE wa.id IS NULL AND sa.profile_id = ?
+                    WHERE wa.id IS NULL AND sa.profile_id = ? {source_filter}
                     GROUP BY sa.similar_artist_name
                     ORDER BY
                         CASE WHEN MAX(sa.last_featured) IS NULL THEN 0 ELSE 1 END,

web_server.py

@@ -39021,7 +39021,8 @@ def get_discover_hero():
         # Get top similar artists (excluding watchlist, cycled by last_featured)
         # Fetch more than needed since strict source filtering may drop many
         pid = get_current_profile_id()
-        similar_artists = database.get_top_similar_artists(limit=200, profile_id=pid)
+        print(f"[Discover Hero] Profile ID: {pid}, Active source: {active_source}")
+        similar_artists = database.get_top_similar_artists(limit=200, profile_id=pid, require_source=active_source)
 
         # FALLBACK: If no similar artists exist, use watchlist artists for Hero section
         if not similar_artists:
@@ -39067,15 +39068,8 @@ def get_discover_hero():
             print(f"[Discover Hero] Returning {len(hero_artists)} watchlist artists as fallback")
             return jsonify({"success": True, "artists": hero_artists, "source": active_source, "fallback": "watchlist"})
 
-        # Filter to artists that have the appropriate ID for the active source
+        # Artists are already filtered by source in SQL — no post-filter needed
-        valid_artists = []
+        valid_artists = list(similar_artists)
-        for artist in similar_artists:
-            if active_source == 'spotify' and artist.similar_artist_spotify_id:
-                valid_artists.append(artist)
-            elif active_source == 'deezer' and getattr(artist, 'similar_artist_deezer_id', None):
-                valid_artists.append(artist)
-            elif active_source == 'itunes' and artist.similar_artist_itunes_id:
-                valid_artists.append(artist)
 
         # FALLBACK: If no valid artists for fallback source, try to resolve IDs on-the-fly
         if active_source in ('itunes', 'deezer') and not valid_artists:
@@ -39198,20 +39192,14 @@ def get_discover_similar_artists():
         database = get_database()
         active_source = _get_active_discovery_source()
 
-        similar_artists = database.get_top_similar_artists(limit=200, profile_id=get_current_profile_id())
+        similar_artists = database.get_top_similar_artists(limit=200, profile_id=get_current_profile_id(), require_source=active_source)
 
         if not similar_artists:
             return jsonify({"success": True, "artists": [], "source": active_source, "count": 0})
 
-        # Filter to artists with valid ID for active source (strict — no cross-source)
+        # Artists already filtered by source in SQL
         result_artists = []
         for artist in similar_artists:
-            if active_source == 'spotify' and not artist.similar_artist_spotify_id:
-                continue
-            if active_source == 'deezer' and not getattr(artist, 'similar_artist_deezer_id', None) and not artist.similar_artist_itunes_id:
-                continue
-            if active_source == 'itunes' and not artist.similar_artist_itunes_id:
-                continue
 
             if active_source == 'spotify':
                 artist_id = artist.similar_artist_spotify_id