feat(settings): add extension verification browser mode preference

Let users choose whether signed-session verification opens in the
external browser or in-app browser first, with automatic fallback to
the other mode when launch fails.

lib/models/settings.dart

@@ -43,14 +43,15 @@ class AppSettings {
   final String singleFilenameFormat;
   final String albumFolderStructure;
   final bool showExtensionStore;
+  final String
+  extensionVerificationBrowserMode; // 'external_first' or 'in_app_first'
   final String locale;
   final String lyricsMode;
   final String
   tidalHighFormat; // Legacy key for 320kbps lossy output format: 'mp3_320', 'aac_320', 'opus_256', or 'opus_128'
   final bool
   useAllFilesAccess; // Android 13+ only: enable MANAGE_EXTERNAL_STORAGE
-  final bool
-  autoExportFailedDownloads;
+  final bool autoExportFailedDownloads;
   final String
   downloadNetworkMode; // 'any' = WiFi + Mobile, 'wifi_only' = WiFi only
   final bool
@@ -66,16 +67,13 @@ class AppSettings {
   final String localLibraryPath;
   final String
   localLibraryBookmark; // Base64-encoded iOS security-scoped bookmark
-  final bool
-  localLibraryShowDuplicates;
+  final bool localLibraryShowDuplicates;
   final String
   localLibraryAutoScan; // Auto-scan mode: 'off', 'on_open', 'daily', 'weekly'
 
-  final bool
-  hasCompletedTutorial;
+  final bool hasCompletedTutorial;
 
-  final List<String>
-  lyricsProviders;
+  final List<String> lyricsProviders;
   final bool
   lyricsIncludeTranslationNetease; // Append translated lyrics (Netease)
   final bool
@@ -90,8 +88,7 @@ class AppSettings {
   final String
   lastSeenVersion; // Last app version the user has acknowledged (e.g. '3.7.0')
 
-  final bool
-  deduplicateDownloads;
+  final bool deduplicateDownloads;
   final bool saveDownloadHistory;
 
   final String playerMode;
@@ -132,6 +129,7 @@ class AppSettings {
     this.singleFilenameFormat = '{title} - {artist}',
     this.albumFolderStructure = 'artist_album',
     this.showExtensionStore = true,
+    this.extensionVerificationBrowserMode = 'external_first',
     this.locale = 'system',
     this.lyricsMode = 'embed',
     this.tidalHighFormat = 'mp3_320',
@@ -199,6 +197,7 @@ class AppSettings {
     String? singleFilenameFormat,
     String? albumFolderStructure,
     bool? showExtensionStore,
+    String? extensionVerificationBrowserMode,
     String? locale,
     String? lyricsMode,
     String? tidalHighFormat,
@@ -274,6 +273,9 @@ class AppSettings {
       singleFilenameFormat: singleFilenameFormat ?? this.singleFilenameFormat,
       albumFolderStructure: albumFolderStructure ?? this.albumFolderStructure,
       showExtensionStore: showExtensionStore ?? this.showExtensionStore,
+      extensionVerificationBrowserMode:
+          extensionVerificationBrowserMode ??
+          this.extensionVerificationBrowserMode,
       locale: locale ?? this.locale,
       lyricsMode: lyricsMode ?? this.lyricsMode,
       tidalHighFormat: tidalHighFormat ?? this.tidalHighFormat,

lib/models/settings.g.dart

@@ -48,6 +48,8 @@ AppSettings _$AppSettingsFromJson(Map<String, dynamic> json) => AppSettings(
   albumFolderStructure:
       json['albumFolderStructure'] as String? ?? 'artist_album',
   showExtensionStore: json['showExtensionStore'] as bool? ?? true,
+  extensionVerificationBrowserMode:
+      json['extensionVerificationBrowserMode'] as String? ?? 'external_first',
   locale: json['locale'] as String? ?? 'system',
   lyricsMode: json['lyricsMode'] as String? ?? 'embed',
   tidalHighFormat: json['tidalHighFormat'] as String? ?? 'mp3_320',
@@ -125,6 +127,7 @@ Map<String, dynamic> _$AppSettingsToJson(
   'singleFilenameFormat': instance.singleFilenameFormat,
   'albumFolderStructure': instance.albumFolderStructure,
   'showExtensionStore': instance.showExtensionStore,
+  'extensionVerificationBrowserMode': instance.extensionVerificationBrowserMode,
   'locale': instance.locale,
   'lyricsMode': instance.lyricsMode,
   'tidalHighFormat': instance.tidalHighFormat,

lib/providers/download_queue_provider.dart

@@ -2098,6 +2098,7 @@ class DownloadQueueNotifier extends Notifier<DownloadQueueState> {
 
     final opened = await openPendingExtensionVerification(
       normalizedExtensionId,
+      browserMode: ref.read(settingsProvider).extensionVerificationBrowserMode,
     );
     if (!opened) return false;
 

lib/providers/settings_provider.dart

@@ -28,6 +28,10 @@ class SettingsNotifier extends Notifier<AppSettings> {
     'album',
     'playlist',
   };
+  static const Set<String> _extensionVerificationBrowserModeValues = {
+    'external_first',
+    'in_app_first',
+  };
 
   final Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
   final FlutterSecureStorage _secureStorage = const FlutterSecureStorage();
@@ -79,6 +83,10 @@ class SettingsNotifier extends Notifier<AppSettings> {
           defaultSearchTab: sanitizedDefaultSearchTab,
           defaultService: loaded.defaultService,
           searchProvider: loaded.searchProvider,
+          extensionVerificationBrowserMode:
+              _normalizeExtensionVerificationBrowserMode(
+                loaded.extensionVerificationBrowserMode,
+              ),
         );
 
         await _runMigrations(prefs);
@@ -270,6 +278,14 @@ class SettingsNotifier extends Notifier<AppSettings> {
     return 'all';
   }
 
+  String _normalizeExtensionVerificationBrowserMode(String value) {
+    final normalized = value.trim().toLowerCase();
+    if (_extensionVerificationBrowserModeValues.contains(normalized)) {
+      return normalized;
+    }
+    return 'external_first';
+  }
+
   String? _sanitizeRetiredBuiltInProviderId(String? providerId) {
     final normalized = providerId?.trim().toLowerCase();
     if (normalized == null || normalized.isEmpty) return providerId;
@@ -557,6 +573,14 @@ class SettingsNotifier extends Notifier<AppSettings> {
     _saveSettings();
   }
 
+  void setExtensionVerificationBrowserMode(String mode) {
+    state = state.copyWith(
+      extensionVerificationBrowserMode:
+          _normalizeExtensionVerificationBrowserMode(mode),
+    );
+    _saveSettings();
+  }
+
   void setLocale(String locale) {
     state = state.copyWith(locale: locale);
     _saveSettings();

lib/providers/track_provider.dart

@@ -686,6 +686,9 @@ class TrackNotifier extends Notifier<TrackState> {
     try {
       final opened = await openPendingExtensionVerification(
         normalizedExtensionId,
+        browserMode: ref
+            .read(settingsProvider)
+            .extensionVerificationBrowserMode,
       );
       if (!opened) return false;
 

lib/screens/settings/app_settings_page.dart

@@ -75,6 +75,12 @@ class AppSettingsPage extends ConsumerWidget {
                         .read(settingsProvider.notifier)
                         .setShowExtensionStore(v),
                   ),
+                  _VerificationBrowserModeSelector(
+                    currentMode: settings.extensionVerificationBrowserMode,
+                    onChanged: (mode) => ref
+                        .read(settingsProvider.notifier)
+                        .setExtensionVerificationBrowserMode(mode),
+                  ),
                   SettingsSwitchItem(
                     icon: Icons.system_update,
                     title: context.l10n.optionsCheckUpdates,
@@ -374,6 +380,90 @@ class _UpdateChannelSelector extends StatelessWidget {
   }
 }
 
+class _VerificationBrowserModeSelector extends StatelessWidget {
+  final String currentMode;
+  final ValueChanged<String> onChanged;
+
+  const _VerificationBrowserModeSelector({
+    required this.currentMode,
+    required this.onChanged,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
+    final normalizedMode = currentMode == 'in_app_first'
+        ? 'in_app_first'
+        : 'external_first';
+
+    return Column(
+      mainAxisSize: MainAxisSize.min,
+      children: [
+        Padding(
+          padding: const EdgeInsets.all(20),
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              Row(
+                children: [
+                  Icon(
+                    Icons.open_in_browser,
+                    color: colorScheme.onSurfaceVariant,
+                    size: 24,
+                  ),
+                  const SizedBox(width: 16),
+                  Expanded(
+                    child: Column(
+                      crossAxisAlignment: CrossAxisAlignment.start,
+                      children: [
+                        Text(
+                          'Verification browser',
+                          style: Theme.of(context).textTheme.bodyLarge,
+                        ),
+                        const SizedBox(height: 2),
+                        Text(
+                          normalizedMode == 'external_first'
+                              ? 'Open challenges in the default browser first'
+                              : 'Open challenges in the in-app browser first',
+                          style: Theme.of(context).textTheme.bodyMedium
+                              ?.copyWith(color: colorScheme.onSurfaceVariant),
+                        ),
+                      ],
+                    ),
+                  ),
+                ],
+              ),
+              const SizedBox(height: 16),
+              Row(
+                children: [
+                  _ChannelChip(
+                    label: 'External',
+                    isSelected: normalizedMode == 'external_first',
+                    onTap: () => onChanged('external_first'),
+                  ),
+                  const SizedBox(width: 8),
+                  _ChannelChip(
+                    label: 'In-app',
+                    isSelected: normalizedMode == 'in_app_first',
+                    onTap: () => onChanged('in_app_first'),
+                  ),
+                ],
+              ),
+            ],
+          ),
+        ),
+        Divider(
+          height: 1,
+          thickness: 1,
+          indent: 56,
+          endIndent: 20,
+          color: colorScheme.outlineVariant.withValues(alpha: 0.3),
+        ),
+      ],
+    );
+  }
+}
+
 class _ChannelChip extends StatelessWidget {
   final String label;
   final bool isSelected;

lib/utils/extension_auth_launcher.dart

@@ -27,7 +27,10 @@ bool _containsHttpStatusCode(String message, String code) {
       message.contains('$code;');
 }
 
-Future<bool> openPendingExtensionVerification(String extensionId) async {
+Future<bool> openPendingExtensionVerification(
+  String extensionId, {
+  String browserMode = 'external_first',
+}) async {
   final normalizedExtensionId = extensionId.trim();
   if (normalizedExtensionId.isEmpty) return false;
 
@@ -41,9 +44,17 @@ Future<bool> openPendingExtensionVerification(String extensionId) async {
     final uri = Uri.tryParse(authUrl);
     if (uri == null) return false;
 
-    var launched = await launchUrl(uri, mode: LaunchMode.inAppBrowserView);
+    final preferInApp = browserMode.trim().toLowerCase() == 'in_app_first';
+    final firstMode = preferInApp
+        ? LaunchMode.inAppBrowserView
+        : LaunchMode.externalApplication;
+    final fallbackMode = preferInApp
+        ? LaunchMode.externalApplication
+        : LaunchMode.inAppBrowserView;
+
+    var launched = await launchUrl(uri, mode: firstMode);
     if (!launched) {
-      launched = await launchUrl(uri, mode: LaunchMode.externalApplication);
+      launched = await launchUrl(uri, mode: fallbackMode);
     }
 
     if (launched) {