fix(metadata): resolve album artist consistently across separate downloads

lib/services/download_album_metadata.dart

@@ -0,0 +1,42 @@
+import 'package:spotiflac_android/models/track.dart';
+import 'package:spotiflac_android/services/platform_bridge.dart';
+import 'package:spotiflac_android/utils/logger.dart';
+import 'package:spotiflac_android/utils/string_utils.dart';
+
+final _log = AppLogger('DownloadAlbumMetadata');
+
+/// Resolve the release credit independently of which tracks were selected.
+/// The bridge caches album responses and coalesces concurrent album lookups.
+Future<Track> resolveDownloadAlbumArtist(
+  Track track,
+  String providerId, {
+  Future<Map<String, dynamic>> Function(String, String, String)? loadMetadata,
+}) async {
+  final albumId = normalizeOptionalString(track.albumId);
+  if (albumId == null || providerId.isEmpty) return track;
+  try {
+    final response = await (loadMetadata ?? PlatformBridge.getProviderMetadata)(
+      providerId,
+      'album',
+      albumId,
+    ).timeout(const Duration(seconds: 8));
+    final info = response['album_info'] ?? response['album'] ?? response;
+    if (info is! Map<String, dynamic>) return track;
+    final returnedId = normalizeOptionalString(info['id']?.toString());
+    if (returnedId != null && returnedId != albumId) return track;
+    // Only album-level credits are authoritative. Track artists may include
+    // guests, and compilations/joint albums must retain their complete credit.
+    String? artist;
+    for (final key in ['album_artist', 'artists', 'artist']) {
+      final value = info[key];
+      if (value is String) artist = normalizeOptionalString(value);
+      if (artist != null) break;
+    }
+    return artist == null || artist == track.albumArtist
+        ? track
+        : track.copyWith(albumArtist: artist);
+  } catch (error) {
+    _log.w('Album credit lookup failed; keeping track metadata: $error');
+    return track;
+  }
+}