CmdpPal: SearchBox visibility and async loading race (#42783)

## Summary of the Pull Request

This PR introduces two related fixes to improve the stability and
reliability of navigation and search UI behavior in the shell:

- **Ensure search box visibility is correctly updated**  
- `ShellViewModel` previously set `IsSearchBoxVisible` after navigation
to the page, but didn’t update it when the value changed. While the
value isn’t expected to change dynamically, the property initialization
is asynchronous, which could cause a race condition.
- As a defensive measure, this also changes the default value of
uninitialized property to make it visible by default.

- **Cancel asynchronous focus placement if navigation changes**  
- Ensures that any pending asynchronous focus operation is cancelled
when another navigation occurs before it completes.


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## PR Checklist

- [x] Closes: #42782
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Core/Microsoft.CmdPal.Core.ViewModels/PageViewModel.cs

@@ -68,7 +68,7 @@ public partial class PageViewModel : ExtensionObjectViewModel, IPageContext
     // `IsLoading` property as a combo of this value and `IsInitialized`
     public bool ModelIsLoading { get; protected set; } = true;
 
-    public bool HasSearchBox { get; protected set; }
+    public bool HasSearchBox { get; protected set; } = true;
 
     public IconInfoViewModel Icon { get; protected set; }
 

src/modules/cmdpal/Core/Microsoft.CmdPal.Core.ViewModels/ShellViewModel.cs

@@ -2,6 +2,7 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.ComponentModel;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using CommunityToolkit.Mvvm.Messaging;
@@ -48,6 +49,9 @@ public partial class ShellViewModel : ObservableObject,
             var oldValue = _currentPage;
             if (SetProperty(ref _currentPage, value))
             {
+                oldValue.PropertyChanged -= CurrentPage_PropertyChanged;
+                value.PropertyChanged += CurrentPage_PropertyChanged;
+
                 if (oldValue is IDisposable disposable)
                 {
                     try
@@ -63,6 +67,14 @@ public partial class ShellViewModel : ObservableObject,
         }
     }
 
+    private void CurrentPage_PropertyChanged(object? sender, PropertyChangedEventArgs e)
+    {
+        if (e.PropertyName == nameof(PageViewModel.HasSearchBox))
+        {
+            IsSearchBoxVisible = CurrentPage.HasSearchBox;
+        }
+    }
+
     private IPage? _rootPage;
 
     private bool _isNested;

src/modules/cmdpal/Microsoft.CmdPal.UI/Pages/ShellPage.xaml.cs

@@ -48,7 +48,8 @@ public sealed partial class ShellPage : Microsoft.UI.Xaml.Controls.Page,
     IRecipient<ShowConfirmationMessage>,
     IRecipient<ShowToastMessage>,
     IRecipient<NavigateToPageMessage>,
-    INotifyPropertyChanged
+    INotifyPropertyChanged,
+    IDisposable
 {
     private readonly DispatcherQueue _queue = DispatcherQueue.GetForCurrentThread();
 
@@ -65,6 +66,9 @@ public sealed partial class ShellPage : Microsoft.UI.Xaml.Controls.Page,
 
     private SettingsWindow? _settingsWindow;
 
+    private CancellationTokenSource? _focusAfterLoadedCts;
+    private WeakReference<Page>? _lastNavigatedPageRef;
+
     public ShellViewModel ViewModel { get; private set; } = App.Current.Services.GetService<ShellViewModel>()!;
 
     public event PropertyChangedEventHandler? PropertyChanged;
@@ -488,6 +492,7 @@ public sealed partial class ShellPage : Microsoft.UI.Xaml.Controls.Page,
 
         if (e.Content is Page element)
         {
+            _lastNavigatedPageRef = new WeakReference<Page>(element);
             element.Loaded += FocusAfterLoaded;
         }
     }
@@ -497,6 +502,18 @@ public sealed partial class ShellPage : Microsoft.UI.Xaml.Controls.Page,
         var page = (Page)sender;
         page.Loaded -= FocusAfterLoaded;
 
+        // Only handle focus for the latest navigated page
+        if (_lastNavigatedPageRef is null || !_lastNavigatedPageRef.TryGetTarget(out var last) || !ReferenceEquals(page, last))
+        {
+            return;
+        }
+
+        // Cancel any previous pending focus work
+        _focusAfterLoadedCts?.Cancel();
+        _focusAfterLoadedCts?.Dispose();
+        _focusAfterLoadedCts = new CancellationTokenSource();
+        var token = _focusAfterLoadedCts.Token;
+
         AnnounceNavigationToPage(page);
 
         var shouldSearchBoxBeVisible = ViewModel.CurrentPage?.HasSearchBox ?? false;
@@ -509,34 +526,57 @@ public sealed partial class ShellPage : Microsoft.UI.Xaml.Controls.Page,
         }
         else
         {
-            _ = Task.Run(async () =>
+            _ = Task.Run(
-            {
+                async () =>
-                await page.DispatcherQueue.EnqueueAsync(async () =>
                 {
-                    // I hate this so much, but it can take a while for the page to be ready to accept focus;
+                    if (token.IsCancellationRequested)
-                    // focusing page with MarkdownTextBlock takes up to 5 attempts (* 100ms delay between attempts)
-                    for (var i = 0; i < 10; i++)
                     {
-                        if (FocusManager.FindFirstFocusableElement(page) is FrameworkElement frameworkElement)
+                        return;
-                        {
-                            var set = frameworkElement.Focus(FocusState.Programmatic);
-                            if (set)
-                            {
-                                break;
-                            }
-                        }
-
-                        await Task.Delay(100);
                     }
 
-                    // Update the search box visibility based on the current page:
+                    try
-                    // - We do this here after navigation so the focus is not jumping around too much,
+                    {
-                    //   it messes with screen readers if we do it too early
+                        await page.DispatcherQueue.EnqueueAsync(
-                    // - Since this should hide the search box on content pages, it's not a problem if we
+                            async () =>
-                    //   wait for the code above to finish trying to focus the content
+                            {
-                    ViewModel.IsSearchBoxVisible = ViewModel.CurrentPage?.HasSearchBox ?? false;
+                                // I hate this so much, but it can take a while for the page to be ready to accept focus;
-                });
+                                // focusing page with MarkdownTextBlock takes up to 5 attempts (* 100ms delay between attempts)
-            });
+                                for (var i = 0; i < 10; i++)
+                                {
+                                    token.ThrowIfCancellationRequested();
+
+                                    if (FocusManager.FindFirstFocusableElement(page) is FrameworkElement frameworkElement)
+                                    {
+                                        var set = frameworkElement.Focus(FocusState.Programmatic);
+                                        if (set)
+                                        {
+                                            break;
+                                        }
+                                    }
+
+                                    await Task.Delay(100, token);
+                                }
+
+                                token.ThrowIfCancellationRequested();
+
+                                // Update the search box visibility based on the current page:
+                                // - We do this here after navigation so the focus is not jumping around too much,
+                                //   it messes with screen readers if we do it too early
+                                // - Since this should hide the search box on content pages, it's not a problem if we
+                                //   wait for the code above to finish trying to focus the content
+                                ViewModel.IsSearchBoxVisible = ViewModel.CurrentPage?.HasSearchBox ?? false;
+                            });
+                    }
+                    catch (OperationCanceledException)
+                    {
+                        // Swallow cancellation - another FocusAfterLoaded invocation superseded this one
+                    }
+                    catch (Exception ex)
+                    {
+                        Logger.LogError("Error during FocusAfterLoaded async focus work", ex);
+                    }
+                },
+                token);
         }
     }
 
@@ -665,4 +705,11 @@ public sealed partial class ShellPage : Microsoft.UI.Xaml.Controls.Page,
             Logger.LogError("Error handling mouse button press event", ex);
         }
     }
+
+    public void Dispose()
+    {
+        _focusAfterLoadedCts?.Cancel();
+        _focusAfterLoadedCts?.Dispose();
+        _focusAfterLoadedCts = null;
+    }
 }