fix(app): fail closed on invalid connection mode state

Restore SOCKS5 only from the current proxy value and keep UI state unchanged when persistence fails.

lib/logic/connection_settings.dart

@@ -18,23 +18,32 @@ abstract final class ConnectionSettings {
     final prefs = await SharedPreferences.getInstance();
     final storedMode = prefs.getString(_modeKey);
 
-    // Any unrecognized value (including the pre-V3 'auto') is TUN. 'proxy' is
-    // the only persisted value that selects the SOCKS5 mode.
+    // Only the explicit current proxy value restores SOCKS5. Unknown and
+    // obsolete values, including the former 'auto'/'ass' labels, fail closed
+    // to full-tunnel TUN instead of silently selecting a weaker route.
     _mode = storedMode == ConnectionMode.proxy.name
         ? ConnectionMode.proxy
         : ConnectionMode.tun;
 
     if (storedMode != _mode.name) {
-      await prefs.setString(_modeKey, _mode.name);
+      final migrated = await prefs.setString(_modeKey, _mode.name);
+      if (!migrated) {
+        throw StateError('Could not persist migrated connection mode.');
+      }
     }
 
     _initialized = true;
   }
 
-  static Future<void> setMode(ConnectionMode mode) async {
+  static Future<bool> setMode(ConnectionMode mode) async {
+    if (_initialized && _mode == mode) return true;
+
+    final prefs = await SharedPreferences.getInstance();
+    final saved = await prefs.setString(_modeKey, mode.name);
+    if (!saved) return false;
+
     _mode = mode;
     _initialized = true;
-    final prefs = await SharedPreferences.getInstance();
-    await prefs.setString(_modeKey, mode.name);
+    return true;
   }
 }

lib/screens/settings/in_settings/connection_mode.dart

@@ -51,8 +51,14 @@ class _ConnectionModeTileState extends State<ConnectionModeTile> {
       return;
     }
 
-    await ConnectionSettings.setMode(next);
+    final saved = await ConnectionSettings.setMode(next);
     if (!mounted) return;
+    if (!saved) {
+      ScaffoldMessenger.of(context).showSnackBar(
+        const SnackBar(content: Text('Could not save connection mode.')),
+      );
+      return;
+    }
 
     setState(() {
       _mode = next;
@@ -61,10 +67,6 @@ class _ConnectionModeTileState extends State<ConnectionModeTile> {
     widget.onChanged?.call(next);
   }
 
-  /// Recovers from an orphaned proxy: tear the runtime down and start a fresh
-  /// session so a readable set of credentials exists again. No rewarded ad —
-  /// the user is repairing a connection they already paid for, not opening a
-  /// new one.
   Future<void> _reconnect() async {
     if (_reconnecting) return;
     final vpn = context.read<VpnConnection>();
@@ -168,11 +170,6 @@ class _ConnectionModeTileState extends State<ConnectionModeTile> {
             builder: (context, vpn, _) {
               final session = vpn.activeSocksSession;
               if (session == null) {
-                // The proxy can be running while this session is unknown:
-                // Android killed the app process, the foreground service kept
-                // the listener alive, and its credentials existed only in the
-                // memory that died with it. Saying "Connect" there would be a
-                // lie — the user is already connected.
                 final orphaned = vpn.status == VpnStatus.connected &&
                     vpn.adoptedRunningRuntime;
                 if (orphaned) {