fix(download): restore fast SQL-only duplicate check so huge playlists queue again

lib/providers/download_history_provider.dart

@@ -1063,34 +1063,24 @@ final downloadHistoryExistsProvider = FutureProvider.autoDispose
       );
     });
 
+// Deliberately no per-row verifyOrRepairHistoryItem here (issue #495): on a
+// >500-track playlist that verify pass meant one SAF stat round-trip per
+// already-downloaded track, and any loadedIndexVersion bump mid-pass restarted
+// it from zero — above ~500 tracks the future never settled and "Download all"
+// silently did nothing. Stale rows are reconciled by the startup repair and
+// orphan-cleanup passes; the single-track provider above keeps the verify.
 final downloadHistoryBatchExistsProvider = FutureProvider.autoDispose
     .family<Set<String>, HistoryBatchLookupRequest>((ref, request) async {
       ref.watch(
         downloadHistoryProvider.select((state) => state.loadedIndexVersion),
       );
-      final notifier = ref.read(downloadHistoryProvider.notifier);
       final rows = await HistoryDatabase.instance.findExistingTracks(
         request.tracks,
       );
-      final found = <String>{};
-      const chunkSize = 16;
-      for (var start = 0; start < rows.length; start += chunkSize) {
-        final end = min(start + chunkSize, rows.length);
-        final checks = await Future.wait(
-          List.generate(end - start, (offset) async {
-            final index = start + offset;
-            final row = rows[index];
-            if (row == null) return null;
-            final exists = await notifier.verifyOrRepairHistoryItem(
-              DownloadHistoryItem.fromJson(row),
-            );
-            if (!exists) return null;
-            return request.tracks[index].lookupKey;
-          }),
-        );
-        found.addAll(checks.whereType<String>());
-      }
-      return found;
+      return <String>{
+        for (var i = 0; i < rows.length; i++)
+          if (rows[i] != null) request.tracks[i].lookupKey,
+      };
     });
 
 class DownloadedAlbumTracksRequest {

lib/widgets/track_detail_actions.dart

@@ -7,6 +7,7 @@ import 'package:spotiflac_android/providers/extension_provider.dart';
 import 'package:spotiflac_android/providers/library_collections_provider.dart';
 import 'package:spotiflac_android/providers/local_library_provider.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
+import 'package:spotiflac_android/utils/logger.dart';
 import 'package:spotiflac_android/widgets/download_service_picker.dart';
 import 'package:spotiflac_android/widgets/view_queue_snackbar_action.dart';
 
@@ -142,13 +143,20 @@ Future<void> queueTracksSkippingDownloaded(
   final historyLookups = tracks
       .map(historyLookupForTrack)
       .toList(growable: false);
-  final existingHistoryKeys = skipExisting
-      ? await ref.read(
-          downloadHistoryBatchExistsProvider(
-            HistoryBatchLookupRequest(historyLookups),
-          ).future,
-        )
-      : const <String>{};
+  Set<String> existingHistoryKeys = const {};
+  if (skipExisting) {
+    try {
+      existingHistoryKeys = await ref.read(
+        downloadHistoryBatchExistsProvider(
+          HistoryBatchLookupRequest(historyLookups),
+        ).future,
+      );
+    } catch (e) {
+      // Queueing without the skip beats silently doing nothing: several
+      // callers fire this flow unawaited, so a throw here would vanish.
+      AppLogger('DownloadFlow').w('Duplicate check failed, queueing all: $e');
+    }
+  }
   if (!context.mounted) return;
   final localLibState =
       (skipExisting &&