fix: gate frontend polling timers and intercept unauthenticated requests to prevent 403 errors on login screen

frontend/lib/core/network/api_constants.dart

@@ -33,6 +33,21 @@ class ApiConstants {
       InterceptorsWrapper(
         onRequest: (options, handler) {
           options.baseUrl = _baseUrl;
+
+          // Prevent unauthenticated or malformed token requests from hitting the server
+          final authHeader = options.headers['Authorization']?.toString() ?? '';
+          if (authHeader == 'Bearer null' ||
+              authHeader == 'Bearer ' ||
+              authHeader == 'Bearer undefined') {
+            return handler.reject(
+              DioException(
+                requestOptions: options,
+                type: DioExceptionType.cancel,
+                error: 'Unauthenticated request cancelled: Invalid Authorization header ($authHeader)',
+              ),
+            );
+          }
+
           return handler.next(options);
         },
       ),

frontend/lib/ui/providers/auth_provider.dart

@@ -77,44 +77,16 @@ class AuthNotifier extends AsyncNotifier<UserModel?> {
   }
 
   void _invalidateAllProviders() {
-    // Documents & folders
+    // Only reset persistent filter and navigation states.
+    // autoDispose FutureProviders clean themselves up automatically when screens unmount;
+    // invalidating them during logout triggers unnecessary unauthenticated API requests.
     ref.invalidate(documentQueryProvider);
-    ref.invalidate(documentPageProvider);
-    ref.invalidate(documentMutationProvider);
-    ref.invalidate(printQueueMutationProvider);
-    ref.invalidate(trashMutationProvider);
-    ref.invalidate(requirementMutationProvider);
-    ref.invalidate(folderMutationProvider);
     ref.invalidate(openedFolderProvider);
-
-    // Archives
     ref.invalidate(archiveQueryProvider);
-    ref.invalidate(archiveDocumentQueryProvider);
-    ref.invalidate(archiveMutationProvider);
-
-    // Students
     ref.invalidate(studentQueryProvider);
-    ref.invalidate(studentMutationProvider);
-
-    // Users & notifications
-    ref.invalidate(usersProvider);
-    ref.invalidate(notificationsProvider);
-
-    // Navigation
     ref.invalidate(activeTabProvider);
 
-    // Dashboard
-    ref.invalidate(dashboardDataProvider);
-
-    // Setup / Settings
-    ref.invalidate(academicYearsListProvider);
-    ref.invalidate(sectionsListProvider);
-    ref.invalidate(gradeLevelsListProvider);
-    ref.invalidate(setupMutationProvider);
-
-    // Reports
     ref.invalidate(selectedAcademicYearIdProvider);
-    ref.invalidate(academicYearsProvider);
     ref.invalidate(selectedGradeLevelProvider);
     ref.invalidate(selectedSectionIdProvider);
     ref.invalidate(selectedStatusFilterProvider);
@@ -123,9 +95,6 @@ class AuthNotifier extends AsyncNotifier<UserModel?> {
     ref.invalidate(missingDocsFilterExpandedProvider);
     ref.invalidate(yearlyComparisonSelectedYearsProvider);
     ref.invalidate(yearlyComparisonSelectedStatusesProvider);
-
-    // OCR
-    ref.invalidate(ocrProvider);
   }
 
   Future<void> refreshUser() async {

frontend/lib/ui/screens/archives/archives_screen.dart

@@ -84,9 +84,12 @@ class _ArchivesScreenState extends ConsumerState<ArchivesScreen>
     _tabController = TabController(length: 2, vsync: this);
 
     _pollingTimer = Timer.periodic(const Duration(seconds: 15), (_) {
-      if (!mounted) return;
-      ref.invalidate(archiveStudentFoldersProvider);
-      ref.invalidate(archiveDocumentPageProvider);
+      if (mounted &&
+          ref.read(authProvider).value != null &&
+          ref.read(activeTabProvider) == 'Archives') {
+        ref.invalidate(archiveStudentFoldersProvider);
+        ref.invalidate(archiveDocumentPageProvider);
+      }
     });
 
     _tabController.addListener(() {

frontend/lib/ui/screens/dashboard/dashboard_screen.dart

@@ -99,7 +99,9 @@ class _DashboardScreenState extends ConsumerState<DashboardScreen> {
   void _startPolling() {
     _pollingTimer?.cancel();
     _pollingTimer = Timer.periodic(const Duration(seconds: 5), (_) {
-      if (mounted && ref.read(activeTabProvider) == 'Dashboard') {
+      if (mounted &&
+          ref.read(authProvider).value != null &&
+          ref.read(activeTabProvider) == 'Dashboard') {
         ref.invalidate(dashboardDataProvider);
         ref.invalidate(dashboardKpisProvider);
         ref.read(notificationsProvider.notifier).refreshNotifications();

frontend/lib/ui/screens/documents/documents_screen.dart

@@ -13,6 +13,7 @@ import '../../shared/inputs/app_search_bar.dart';
 import '../../shared/buttons/primary_button.dart';
 import '../../providers/document_provider.dart';
 import '../../providers/student_provider.dart';
+import '../../providers/auth_provider.dart';
 import '../../shared/widgets/app_pagination.dart';
 import '../../providers/navigation_provider.dart';
 
@@ -95,7 +96,9 @@ class _DocumentsScreenState extends ConsumerState<DocumentsScreen>
     _searchFocusNode.addListener(_onSearchFocusChanged);
 
     _pollingTimer = Timer.periodic(const Duration(seconds: 15), (_) {
-      if (mounted) {
+      if (mounted &&
+          ref.read(authProvider).value != null &&
+          ref.read(activeTabProvider) == 'Documents') {
         if (_tabController.index == 0) {
           ref.invalidate(foldersProvider);
           ref.invalidate(studentFoldersProvider);

frontend/lib/ui/screens/reports/reports_screen.dart

@@ -13,6 +13,7 @@ import '../../shared/buttons/primary_button.dart';
 import '../../shared/cards/stat_card.dart';
 import '../../providers/reports_provider.dart';
 import '../../providers/navigation_provider.dart';
+import '../../providers/auth_provider.dart';
 import '../../shared/dialogs/file_save_preview_dialog.dart';
 import '../documents/widgets/student_profile_modal.dart';
 import 'package:fl_chart/fl_chart.dart';
@@ -59,7 +60,9 @@ class _ReportsScreenState extends ConsumerState<ReportsScreen> {
 
       // Polling every 5 seconds
       _pollingTimer = Timer.periodic(const Duration(seconds: 5), (_) {
-        if (mounted && ref.read(activeTabProvider) == 'Reports') {
+        if (mounted &&
+            ref.read(authProvider).value != null &&
+            ref.read(activeTabProvider) == 'Reports') {
           _refreshData();
         }
       });

frontend/lib/ui/screens/settings/teacher_management_screen.dart

@@ -7,6 +7,7 @@ import '../../shared/inputs/custom_text_field.dart';
 import '../../shared/buttons/primary_button.dart';
 import '../../providers/users_provider.dart';
 import '../../providers/setup_provider.dart';
+import '../../providers/auth_provider.dart';
 import '../../../domain/entities/setup_models.dart';
 import '../../../domain/entities/system_user.dart';
 import '../../shared/dialogs/error_dialog.dart';
@@ -63,7 +64,9 @@ class _TeacherManagementModalState extends ConsumerState<TeacherManagementModal>
 
     // Polling every 5 seconds
     _pollingTimer = Timer.periodic(const Duration(seconds: 5), (_) {
-      _refreshData();
+      if (mounted && ref.read(authProvider).value != null) {
+        _refreshData();
+      }
     });
   }