feat(folders): Preserve feature state on server-side errors

lib/core/auth/api_auth_interceptor.dart

@@ -35,6 +35,13 @@ class ApiAuthInterceptor extends Interceptor {
     '/api/v1/configs/models',
   };
 
+  // Endpoints for features that can be disabled server-side.
+  // A 403 on these indicates the feature is disabled, not an auth failure.
+  static const Set<String> _featureEndpoints = {
+    '/api/v1/folders/',
+    '/api/v1/folders',
+  };
+
   ApiAuthInterceptor({
     String? authToken,
     this.onAuthTokenInvalid,
@@ -79,6 +86,20 @@ class ApiAuthInterceptor extends Interceptor {
     return _optionalAuthEndpoints.contains(path);
   }
 
+  /// Check if endpoint is for a feature that can be disabled server-side.
+  /// A 403 on these indicates feature disabled, not an auth failure.
+  bool _isFeatureEndpoint(String path) {
+    // Direct match for exact paths like /api/v1/folders or /api/v1/folders/
+    if (_featureEndpoints.contains(path)) {
+      return true;
+    }
+    // Check for folder sub-paths (e.g., /api/v1/folders/{id})
+    if (path.startsWith('/api/v1/folders/')) {
+      return true;
+    }
+    return false;
+  }
+
   @override
   void onRequest(RequestOptions options, RequestInterceptorHandler handler) {
     final path = options.path;
@@ -153,9 +174,15 @@ class ApiAuthInterceptor extends Interceptor {
       }
     } else if (statusCode == 403) {
       // 403 on protected endpoints indicates insufficient permissions or invalid token
+      // BUT 403 on feature endpoints indicates the feature is disabled server-side
       final requiresAuth = _requiresAuth(path);
       final optionalAuth = _hasOptionalAuth(path);
-      if (requiresAuth && !optionalAuth) {
+      final isFeatureEndpoint = _isFeatureEndpoint(path);
+      if (isFeatureEndpoint) {
+        DebugLogger.auth(
+          '403 Forbidden on feature endpoint $path - feature likely disabled server-side',
+        );
+      } else if (requiresAuth && !optionalAuth) {
         _notifyAuthFailure(
           '403 Forbidden on protected endpoint $path - notifying app without clearing token',
         );

lib/core/providers/app_providers.dart

@@ -1285,7 +1285,10 @@ class Conversations extends _$Conversations {
           error: error,
           stackTrace: stackTrace,
         );
-        return <Map<String, dynamic>>[];
+        // Preserve the existing enabled state on error (don't override a
+        // previously determined disabled state due to network errors)
+        final currentEnabled = ref.read(foldersFeatureEnabledProvider);
+        return (const <Map<String, dynamic>>[], currentEnabled);
       });
 
       final results = await Future.wait<dynamic>([
@@ -1293,7 +1296,14 @@ class Conversations extends _$Conversations {
         foldersFuture,
       ]);
       final conversations = results[0] as List<Conversation>;
-      final foldersData = results[1] as List<Map<String, dynamic>>;
+      final foldersResult = results[1] as (List<Map<String, dynamic>>, bool);
+      final foldersData = foldersResult.$1;
+      final foldersEnabled = foldersResult.$2;
+
+      // Update the folders feature enabled state
+      ref
+          .read(foldersFeatureEnabledProvider.notifier)
+          .setEnabled(foldersEnabled);
       DebugLogger.log(
         'fetch-ok',
         scope: 'conversations',
@@ -2130,6 +2140,22 @@ final webSearchAvailableProvider = Provider<bool>((ref) {
   );
 });
 
+/// Tracks whether the folders feature is enabled on the server.
+/// When the server returns 403 for folders endpoint, this becomes false.
+final foldersFeatureEnabledProvider =
+    NotifierProvider<FoldersFeatureEnabledNotifier, bool>(
+      FoldersFeatureEnabledNotifier.new,
+    );
+
+class FoldersFeatureEnabledNotifier extends Notifier<bool> {
+  @override
+  bool build() => true;
+
+  void setEnabled(bool enabled) {
+    state = enabled;
+  }
+}
+
 // Folders provider
 @Riverpod(keepAlive: true)
 class Folders extends _$Folders {
@@ -2224,14 +2250,20 @@ class Folders extends _$Folders {
 
   Future<List<Folder>> _load(ApiService api) async {
     try {
-      final foldersData = await api.getFolders();
+      final (foldersData, featureEnabled) = await api.getFolders();
+
+      // Update the folders feature enabled state
+      ref
+          .read(foldersFeatureEnabledProvider.notifier)
+          .setEnabled(featureEnabled);
+
       final folders = foldersData
           .map((folderData) => Folder.fromJson(folderData))
           .toList();
       DebugLogger.log(
         'fetch-ok',
         scope: 'folders',
-        data: {'count': folders.length},
+        data: {'count': folders.length, 'enabled': featureEnabled},
       );
       final sorted = _sort(folders);
       _persistFoldersAsync(sorted);

lib/core/services/api_service.dart

@@ -1123,7 +1123,9 @@ class ApiService {
   }
 
   // Folders
-  Future<List<Map<String, dynamic>>> getFolders() async {
+  /// Returns a record with (folders data, feature enabled flag).
+  /// When the folders feature is disabled server-side (403), returns ([], false).
+  Future<(List<Map<String, dynamic>>, bool)> getFolders() async {
     try {
       final response = await _dio.get('/api/v1/folders/');
       DebugLogger.log(
@@ -1136,15 +1138,27 @@ class ApiService {
       final data = response.data;
       if (data is List) {
         _traceApi('Found ${data.length} folders');
-        return data.cast<Map<String, dynamic>>();
+        return (data.cast<Map<String, dynamic>>(), true);
       } else {
         DebugLogger.warning(
           'unexpected-type',
           scope: 'api/folders',
           data: {'type': data.runtimeType},
         );
-        return [];
+        return (const <Map<String, dynamic>>[], true);
       }
+    } on DioException catch (e) {
+      // 403 indicates folders feature is disabled server-side
+      if (e.response?.statusCode == 403) {
+        DebugLogger.log(
+          'feature-disabled',
+          scope: 'api/folders',
+          data: {'status': 403},
+        );
+        return (const <Map<String, dynamic>>[], false);
+      }
+      DebugLogger.error('fetch-failed', scope: 'api/folders', error: e);
+      rethrow;
     } catch (e) {
       DebugLogger.error('fetch-failed', scope: 'api/folders', error: e);
       rethrow;