Fix: Widget tree stability - move screen creation to build method

lib/core/auth_gate.dart

@@ -156,23 +156,24 @@ class _AuthGateState extends State<AuthGate> with WidgetsBindingObserver {
 
   @override
   Widget build(BuildContext context) {
-    // Not yet initialized - show nothing (brief flash)
-    if (!_isInitialized) {
-      return const SizedBox.shrink();
-    }
-    
-    // Not locked - show the app
-    if (!_isLocked) {
-      return GestureDetector(
-        behavior: HitTestBehavior.translucent,
-        onTap: _recordUserActivity,
-        onPanDown: (_) => _recordUserActivity(),
-        child: widget.child,
-      );
-    }
-    
-    // Locked - show auth screen
-    return _buildLockScreen();
+    // Use Stack to keep widget tree stable during transitions
+    return Stack(
+      children: [
+        // Always keep child in tree (but behind lock screen when locked)
+        Offstage(
+          offstage: _isLocked,
+          child: GestureDetector(
+            behavior: HitTestBehavior.translucent,
+            onTap: _recordUserActivity,
+            onPanDown: (_) => _recordUserActivity(),
+            child: widget.child,
+          ),
+        ),
+        // Lock screen overlay
+        if (_isLocked || !_isInitialized)
+          _buildLockScreen(),
+      ],
+    );
   }
 
   Widget _buildLockScreen() {

lib/main.dart

@@ -115,25 +115,17 @@ class MainScaffold extends StatefulWidget {
 class MainScaffoldState extends State<MainScaffold> {
   int _currentIndex = 0;
   final GlobalKey<WebViewScreenState> _webViewKey = GlobalKey();
-  
-  final List<Widget> _screens = [];
-  
-  @override
-  void initState() {
-    super.initState();
-    _screens.addAll([
-      WebViewScreen(key: _webViewKey),
-      const InputScreen(),
-      const SettingsScreen(),
-    ]);
-  }
 
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       body: IndexedStack(
         index: _currentIndex,
-        children: _screens,
+        children: [
+          WebViewScreen(key: _webViewKey),
+          const InputScreen(),
+          const SettingsScreen(),
+        ],
       ),
       bottomNavigationBar: NavigationBar(
         selectedIndex: _currentIndex,