[QuickAccess] Suppress unhandled XAML exceptions in flyout host

src/settings-ui/QuickAccess.UI/QuickAccessXAML/App.xaml.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using ManagedCommon;
 using Microsoft.UI.Xaml;
 
 namespace Microsoft.PowerToys.QuickAccess;
@@ -14,14 +15,26 @@ public partial class App : Application
     public App()
     {
         InitializeComponent();
+        UnhandledException += App_UnhandledException;
     }
 
     protected override void OnLaunched(LaunchActivatedEventArgs args)
     {
-        var launchContext = QuickAccessLaunchContext.Parse(Environment.GetCommandLineArgs());
-        _window = new MainWindow(launchContext);
-        _window.Closed += OnWindowClosed;
-        _window.Activate();
+        try
+        {
+            var launchContext = QuickAccessLaunchContext.Parse(Environment.GetCommandLineArgs());
+            _window = new MainWindow(launchContext);
+            _window.Closed += OnWindowClosed;
+            _window.Activate();
+        }
+        catch (Exception ex)
+        {
+            // Failing here means the flyout host could not be constructed. Log and exit cleanly
+            // rather than letting the throw bubble out into a stowed XAML failure that crashes
+            // the runner-owned launcher.
+            Logger.LogError("QuickAccess: failed to launch flyout host.", ex);
+            Exit();
+        }
     }
 
     private static void OnWindowClosed(object sender, WindowEventArgs args)
@@ -33,4 +46,13 @@ private static void OnWindowClosed(object sender, WindowEventArgs args)
 
         _window = null;
     }
+
+    private void App_UnhandledException(object sender, Microsoft.UI.Xaml.UnhandledExceptionEventArgs e)
+    {
+        // QuickAccess is a transient launcher flyout owned by the runner. An unhandled XAML
+        // exception here would otherwise be stowed and FailFast the process; mark the event
+        // handled so the next summon can recover. The error is still recorded for diagnostics.
+        Logger.LogError("QuickAccess: unhandled XAML exception.", e.Exception);
+        e.Handled = true;
+    }
 }

src/settings-ui/QuickAccess.UI/QuickAccessXAML/Flyout/ShellPage.xaml.cs

@@ -2,11 +2,13 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using ManagedCommon;
 using Microsoft.PowerToys.QuickAccess.Services;
 using Microsoft.PowerToys.QuickAccess.ViewModels;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Media.Animation;
+using Microsoft.UI.Xaml.Navigation;
 
 namespace Microsoft.PowerToys.QuickAccess.Flyout;
 
@@ -22,6 +24,7 @@ public sealed partial class ShellPage : Page
     public ShellPage()
     {
         InitializeComponent();
+        ContentFrame.NavigationFailed += ContentFrame_NavigationFailed;
     }
 
     public void Initialize(IQuickAccessCoordinator coordinator, LauncherViewModel launcherViewModel, AllAppsViewModel allAppsViewModel)
@@ -65,4 +68,13 @@ internal void RefreshIfAppsList()
             appsListPage.ViewModel?.RefreshSettings();
         }
     }
+
+    private static void ContentFrame_NavigationFailed(object sender, NavigationFailedEventArgs e)
+    {
+        // A page constructor or XAML load failure here would otherwise bubble out of the
+        // Frame and crash the launcher. Log the failure and mark it handled so the flyout
+        // can remain available; the next summon will retry navigation.
+        Logger.LogError($"QuickAccess: navigation to '{e.SourcePageType?.FullName}' failed.", e.Exception);
+        e.Handled = true;
+    }
 }