fix: recover authenticated undergraduate full pages with session guards

mobile/lib/features/school/undergraduate/session.dart

@@ -13,9 +13,14 @@ import 'timetable_adapter.dart';
 import 'exam_adapter.dart';
 import '../school_browser.dart';
 import '../school_browser_diagnostics.dart';
+import '../school_full_page_recovery.dart';
 
 class UndergraduateSession extends ChangeNotifier {
-  UndergraduateSession({this.configureBrowser = configureSchoolBrowser});
+  UndergraduateSession({
+    this.configureBrowser = configureSchoolBrowser,
+    SchoolFullPageRecovery? pageRecovery,
+  }) : _pageRecovery = pageRecovery ?? SchoolFullPageRecovery();
+  final SchoolFullPageRecovery _pageRecovery;
   final SchoolBrowserConfigurator configureBrowser;
   Future<SchoolBrowserInfo>? _browserReady;
   String? browserVersion;
@@ -28,6 +33,7 @@ class UndergraduateSession extends ChangeNotifier {
       _connected = false,
       _loading = false,
       _manualCapture = false,
+      _recoveringPage = false,
       _failed = false,
       _complete = false;
   bool hasOpened = false, awaitingAuthentication = false, logoutFailed = false;
@@ -44,7 +50,8 @@ class UndergraduateSession extends ChangeNotifier {
   int get pageGeneration => _generation;
   bool get requestingExams => query != null;
   bool get canLogout => hasOpened || logoutFailed;
-  bool get busy => _loading || _manualCapture || _itemTimeout != null;
+  bool get busy =>
+      _loading || _manualCapture || _recoveringPage || _itemTimeout != null;
   String get statusLabel => logoutFailed
       ? '退出未完成'
       : _failed
@@ -70,6 +77,8 @@ class UndergraduateSession extends ChangeNotifier {
 
   void _reset() {
     _generation++;
+    _pageRecovery.reset();
+    _recoveringPage = false;
     _cancelTimers();
     _parts.clear();
     _index = 0;
@@ -123,6 +132,7 @@ class UndergraduateSession extends ChangeNotifier {
           return NavigationDecision.navigate;
         },
         onPageStarted: (url) {
+          _pageRecovery.invalidateDocument();
           DiagnosticLog.instance.navigation('undergraduate', 'started', url);
           // Within a batch, type-to-type loads retain their generation. Once
           // published, any new document invalidates the deferred save result.
@@ -130,6 +140,7 @@ class UndergraduateSession extends ChangeNotifier {
             _reset();
           }
           _document++;
+          _recoveringPage = false;
           _poll?.cancel();
           _probeKey = null;
           pendingDraft = null;
@@ -350,6 +361,37 @@ class UndergraduateSession extends ChangeNotifier {
       }
       _connected = true;
       awaitingAuthentication = false;
+      final recovery = await _pageRecovery.tryRestore(
+        web,
+        uri,
+        authenticated: true,
+        documentKey: '$g:$d',
+        isCurrent: () => _valid(g) && d == _document,
+        onStarted: () {
+          _recoveringPage = true;
+          message = '已登录，正在恢复完整教务页面…';
+          _emit();
+        },
+      );
+      if (!_valid(g) || d != _document) return;
+      _recoveringPage = false;
+      if (recovery == FullPageRecoveryResult.restored) {
+        _loading = true;
+        message = '完整页面已恢复，正在检查…';
+        _schedulePoll(g, d, url);
+        _emit();
+        return;
+      }
+      if (recovery == FullPageRecoveryResult.cancelled) {
+        message = '页面已变化，请等待加载完成或重新认证。';
+        _emit();
+        return;
+      }
+      if (recovery == FullPageRecoveryResult.failed) {
+        message = '已登录，但完整教务页面暂未恢复，请重新认证后重试。';
+        _emit();
+        return;
+      }
       if (!requestingExams) {
         message = manualMessage;
         _emit();
@@ -438,7 +480,9 @@ class UndergraduateSession extends ChangeNotifier {
   }
 
   Future<void> readCurrentTimetable() async {
-    if (requestingExams || _manualCapture || !_active) return;
+    if (requestingExams || _manualCapture || _recoveringPage || !_active) {
+      return;
+    }
     final g = _generation, d = _document;
     _manualCapture = true;
     _emit();
@@ -535,6 +579,7 @@ class UndergraduateSession extends ChangeNotifier {
     _disposed = true;
     _active = false;
     _generation++;
+    _pageRecovery.reset();
     _cancelTimers();
     super.dispose();
   }