fixed stale state after logout and replayed or lost share intents

lib/model/account_data.dart

@@ -55,6 +55,15 @@ class AccountData {
     unawaited(_loadWithRetry());
   }
 
+  int _sessionEpoch = 0;
+
+  /// Bumped on every sign-out. Async work captures it when it starts and
+  /// drops its result when it changed meanwhile, so a request of the previous
+  /// account cannot land in the next account's state or cache.
+  int get sessionEpoch => _sessionEpoch;
+
+  bool isCurrentSession(int epoch) => epoch == _sessionEpoch;
+
   String? _username;
   String? _password;
   String? _appPassword;
@@ -109,6 +118,7 @@ class AccountData {
   }
 
   Future<void> removeData() async {
+    _sessionEpoch++;
     _populated = Completer();
     _username = null;
     _password = null;
@@ -263,6 +273,52 @@ class AccountData {
     }
   }
 
+  bool _isUiEngine = false;
+
+  /// Called from `main()`; background entry points never run it.
+  void markUiEngine() => _isUiEngine = true;
+
+  /// Username currently in the keystore. Other engines (widget task, push
+  /// isolates) sign out or in without this instance noticing.
+  Future<String?> readStoredUsername() =>
+      _secureStorage.read(key: _usernameField);
+
+  /// Re-reads the session for long-lived background engines: they load once
+  /// and would otherwise keep acting with an account that signed out in the
+  /// app meanwhile. Keeps the known state when the keystore is unreadable.
+  Future<void> reloadFromStorage() async {
+    // The UI engine performs sign-in and sign-out itself, so its state is
+    // current; re-reading mid sign-out could resurrect the removed account.
+    if (_isUiEngine) return;
+    try {
+      final username = await _secureStorage.read(key: _usernameField);
+      final password = await _secureStorage.read(key: _passwordField);
+      final isDemo = (await _secureStorage.read(key: _demoField)) == 'true';
+      final usesLoginFlow =
+          (await _secureStorage.read(key: _loginFlowField)) == 'true';
+      String? appPassword;
+      String? appPasswordTalk;
+      try {
+        appPassword = await pushSecureStorage.read(key: _appPasswordField);
+        appPasswordTalk = await pushSecureStorage.read(
+          key: _appPasswordTalkField,
+        );
+      } on Object {
+        // Group keystore unavailable: fall back to the real password.
+      }
+      if (username != _username) _sessionEpoch++;
+      _username = username;
+      _password = password;
+      _isDemo = isDemo;
+      _usesLoginFlow = usesLoginFlow;
+      _appPassword = appPassword;
+      _appPasswordTalk = appPasswordTalk;
+      if (!_populated.isCompleted) _populated.complete();
+    } on Object catch (e) {
+      log('AccountData reload failed, keeping loaded state: $e');
+    }
+  }
+
   Future<bool> waitForPopulation() async {
     await _populated.future;
     return isPopulated();