feat: 增加后台恢复处理，优化 WebView 状态管理

lib/main.dart

@@ -27,6 +27,7 @@ const _keyboardAnimationDuration = Duration(milliseconds: 250);
 const _h5DomainCacheUrlKey = 'h5_random_domain_url_v1';
 const _lineProbeTimeout = Duration(seconds: 5);
 const _maxGeneratedLineAttempts = 6;
+const _longBackgroundRefreshThreshold = Duration(minutes: 20);
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
@@ -115,6 +116,8 @@ class _H5ShellPageState extends State<H5ShellPage> with WidgetsBindingObserver {
   int _keyboardSyncToken = 0;
   int _lineGeneration = 0;
   int _h5LineAttempt = 0;
+  int _resumeRecoveryToken = 0;
+  DateTime? _backgroundedAt;
   late ShellBranding _shellBranding;
 
   _H5LineWebViewSlot get _currentSlot => _lineSlot;
@@ -244,10 +247,19 @@ class _H5ShellPageState extends State<H5ShellPage> with WidgetsBindingObserver {
 
   @override
   void didChangeAppLifecycleState(AppLifecycleState state) {
+    if (state == AppLifecycleState.paused ||
+        state == AppLifecycleState.inactive ||
+        state == AppLifecycleState.detached) {
+      _backgroundedAt ??= DateTime.now();
+      return;
+    }
+
     if (state == AppLifecycleState.resumed) {
-      unawaited(_syncShellRequestUrl());
-      unawaited(_syncShellBranding());
-      unawaited(_syncKeyboardState());
+      final backgroundDuration = _backgroundedAt == null
+          ? Duration.zero
+          : DateTime.now().difference(_backgroundedAt!);
+      _backgroundedAt = null;
+      unawaited(_recoverWebViewAfterResume(backgroundDuration));
     }
   }
 
@@ -629,6 +641,97 @@ class _H5ShellPageState extends State<H5ShellPage> with WidgetsBindingObserver {
     return _runJavaScriptSafely(script);
   }
 
+  Future<void> _notifyH5AppResumed(Duration backgroundDuration) {
+    final payload = jsonEncode({
+      'backgroundDurationMs': backgroundDuration.inMilliseconds,
+      'refreshedAt': DateTime.now().millisecondsSinceEpoch,
+    });
+    final script = '''
+(() => {
+  try {
+    const detail = $payload;
+    window.dispatchEvent(new CustomEvent('openim-shell-app-resumed', { detail }));
+  } catch (_) {}
+})();
+''';
+    return _runJavaScriptSafely(script);
+  }
+
+  Future<bool> _isH5RuntimeResponsive() async {
+    try {
+      final result = await _lineSlot.controller.runJavaScriptReturningResult(
+        '''
+(() => {
+  try {
+    return JSON.stringify({
+      marker: 'openim-h5-runtime-alive',
+      readyState: document.readyState,
+      href: window.location.href,
+      now: Date.now()
+    });
+  } catch (_) {
+    return 'openim-h5-runtime-error';
+  }
+})();
+''',
+      ).timeout(const Duration(seconds: 2));
+      return result.toString().contains('openim-h5-runtime-alive');
+    } catch (_) {
+      return false;
+    }
+  }
+
+  Future<Uri> _currentReloadUri({required bool cacheBust}) async {
+    String? currentUrl;
+    try {
+      currentUrl = await _lineSlot.controller.currentUrl();
+    } catch (_) {
+      currentUrl = null;
+    }
+
+    final parsedCurrentUrl =
+        currentUrl == null ? null : Uri.tryParse(currentUrl);
+    final uri = parsedCurrentUrl?.hasScheme == true
+        ? parsedCurrentUrl!
+        : Uri.parse(_lineSlot.line.url);
+
+    if (!cacheBust) {
+      return uri;
+    }
+
+    final queryParameters = Map<String, String>.from(uri.queryParameters)
+      ..['_shell_resume_ts'] = DateTime.now().millisecondsSinceEpoch.toString();
+    return uri.replace(queryParameters: queryParameters);
+  }
+
+  Future<void> _recoverWebViewAfterResume(Duration backgroundDuration) async {
+    final token = ++_resumeRecoveryToken;
+    final generation = _lineGeneration;
+    await _syncShellRequestUrl();
+    await _syncShellBranding();
+    await _syncKeyboardState();
+    await _notifyH5AppResumed(backgroundDuration);
+
+    if (!_isCurrentLineGeneration(generation) ||
+        token != _resumeRecoveryToken ||
+        backgroundDuration < _longBackgroundRefreshThreshold) {
+      return;
+    }
+
+    final responsive = await _isH5RuntimeResponsive();
+    if (!mounted ||
+        !_isCurrentLineGeneration(generation) ||
+        token != _resumeRecoveryToken) {
+      return;
+    }
+
+    _logH5LineDebug(
+      '后台 ${backgroundDuration.inMinutes} 分钟后恢复，'
+      '${responsive ? '刷新 WebView 以拉取最新 H5' : 'WebView JS 无响应，重载当前页'}',
+    );
+    await _reloadCurrentLine(forceRefresh: true);
+  }
+
   Future<void> _handleShellMediaPermissionRequest({
     required int generation,
     required String requestId,
@@ -769,7 +872,7 @@ class _H5ShellPageState extends State<H5ShellPage> with WidgetsBindingObserver {
     await _syncKeyboardState();
   }
 
-  Future<void> _reloadCurrentLine() async {
+  Future<void> _reloadCurrentLine({bool forceRefresh = false}) async {
     final slot = _currentSlot;
     if (slot.availability == _LineAvailability.unavailable ||
         slot.loadError != null) {
@@ -787,7 +890,11 @@ class _H5ShellPageState extends State<H5ShellPage> with WidgetsBindingObserver {
       });
     }
 
-    if (slot.hasLoadedInitialRequest) {
+    if (forceRefresh) {
+      await slot.controller.loadRequest(
+        await _currentReloadUri(cacheBust: true),
+      );
+    } else if (slot.hasLoadedInitialRequest) {
       await slot.controller.reload();
     } else {
       await _loadCurrentLine();