perf(library): stream scans and optimize queue queries

test/download_history_logic_test.dart

@@ -22,6 +22,16 @@ DownloadHistoryItem _historyItem({
 
 void main() {
   group('download history identity', () {
+    test('serializes download timestamps with an explicit UTC offset', () {
+      final item = _historyItem(
+        id: 'utc',
+        filePath: '/music/Album/Same Song.flac',
+        downloadedAt: DateTime(2026, 7, 22, 12, 30),
+      );
+
+      expect(item.toJson()['downloadedAt'], endsWith('Z'));
+    });
+
     test('same track metadata does not merge files from different albums', () {
       final first = _historyItem(
         id: 'first',

test/platform_bridge_metadata_test.dart

@@ -167,4 +167,25 @@ void main() {
     expect(results.single['status'], 'found');
     expect(results.single['relative_dir'], 'Artist/Album');
   });
+
+  test('iOS bookmark access releases the matching native lease', () async {
+    final calls = <MethodCall>[];
+    TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger
+        .setMockMethodCallHandler(backendChannel, (call) async {
+          calls.add(call);
+          if (call.method == 'startAccessingIosBookmark') {
+            return {'path': '/music', 'token': 'lease-1'};
+          }
+          if (call.method == 'stopAccessingIosBookmark') return null;
+          fail('Unexpected method: ${call.method}');
+        });
+
+    final access = await PlatformBridge.startAccessingIosBookmark('bookmark');
+    expect(access?.path, '/music');
+    expect(access?.token, 'lease-1');
+    await PlatformBridge.stopAccessingIosBookmark(access!);
+
+    expect(calls[1].method, 'stopAccessingIosBookmark');
+    expect(calls[1].arguments, {'token': 'lease-1'});
+  });
 }