Cmdpal: user research on extension invokes (#43905)

## Summary of the Pull Request

Added two events that Niels asked for:

- `CmdPal_ExtensionInvoked`
- Track which extensions are being used (e.g., file search, app
launching, calculator, etc.).
    - Properties logged
        - ExtensionId - Unique identifier of the extension provider
        - CommandType - Display name of the command being invoked
        - Success - Whether the command executed successfully
        - ExecutionTimeMs - Execution time in milliseconds
- `CmdPal_SessionDuration`
    - Tracks how long Command Palette stays open (launch → close). 
    - Properties logged
        - DurationMs - Session duration in milliseconds
        - CommandsExecuted - Number of commands executed
        - PagesVisited - Number of pages visited
- DismissalReason - Why the session ended (Escape, LostFocus, Command,
etc.)
        - SearchQueriesCount - Number of search queries executed
        - MaxNavigationDepth - Maximum navigation depth reached
        - ErrorCount - Number of errors encountered



<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist

- [ ] Closes: #xxx
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [x] **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

src/modules/cmdpal/Microsoft.CmdPal.UI/MainWindow.xaml.cs

@@ -52,6 +52,10 @@ public sealed partial class MainWindow : WindowEx,
     IRecipient<ShowWindowMessage>,
     IRecipient<HideWindowMessage>,
     IRecipient<QuitMessage>,
+    IRecipient<NavigateToPageMessage>,
+    IRecipient<NavigationDepthMessage>,
+    IRecipient<SearchQueryMessage>,
+    IRecipient<ErrorOccurredMessage>,
     IRecipient<DragStartedMessage>,
     IRecipient<DragCompletedMessage>,
     IDisposable
@@ -75,6 +79,14 @@ public sealed partial class MainWindow : WindowEx,
     private bool _ignoreHotKeyWhenFullScreen = true;
     private bool _themeServiceInitialized;
 
+    // Session tracking for telemetry
+    private Stopwatch? _sessionStopwatch;
+    private int _sessionCommandsExecuted;
+    private int _sessionPagesVisited;
+    private int _sessionSearchQueriesCount;
+    private int _sessionMaxNavigationDepth;
+    private int _sessionErrorCount;
+
     private DesktopAcrylicController? _acrylicController;
     private SystemBackdropConfiguration? _configurationSource;
     private TimeSpan _autoGoHomeInterval = Timeout.InfiniteTimeSpan;
@@ -123,6 +135,10 @@ public sealed partial class MainWindow : WindowEx,
         WeakReferenceMessenger.Default.Register<QuitMessage>(this);
         WeakReferenceMessenger.Default.Register<ShowWindowMessage>(this);
         WeakReferenceMessenger.Default.Register<HideWindowMessage>(this);
+        WeakReferenceMessenger.Default.Register<NavigateToPageMessage>(this);
+        WeakReferenceMessenger.Default.Register<NavigationDepthMessage>(this);
+        WeakReferenceMessenger.Default.Register<SearchQueryMessage>(this);
+        WeakReferenceMessenger.Default.Register<ErrorOccurredMessage>(this);
         WeakReferenceMessenger.Default.Register<DragStartedMessage>(this);
         WeakReferenceMessenger.Default.Register<DragCompletedMessage>(this);
 
@@ -524,6 +540,11 @@ public sealed partial class MainWindow : WindowEx,
     {
         var settings = App.Current.Services.GetService<SettingsModel>()!;
 
+        // Start session tracking
+        _sessionStopwatch = Stopwatch.StartNew();
+        _sessionCommandsExecuted = 0;
+        _sessionPagesVisited = 0;
+
         ShowHwnd(message.Hwnd, settings.SummonOn);
     }
 
@@ -532,6 +553,7 @@ public sealed partial class MainWindow : WindowEx,
         // This might come in off the UI thread. Make sure to hop back.
         DispatcherQueue.TryEnqueue(() =>
         {
+            EndSession("Hide");
             HideWindow();
         });
     }
@@ -551,10 +573,67 @@ public sealed partial class MainWindow : WindowEx,
         // This might come in off the UI thread. Make sure to hop back.
         DispatcherQueue.TryEnqueue(() =>
         {
+            EndSession("Dismiss");
             HideWindow();
         });
     }
 
+    // Session telemetry: Track metrics during the Command Palette session
+    // These receivers increment counters that are sent when EndSession is called
+    public void Receive(NavigateToPageMessage message)
+    {
+        _sessionPagesVisited++;
+    }
+
+    public void Receive(NavigationDepthMessage message)
+    {
+        if (message.Depth > _sessionMaxNavigationDepth)
+        {
+            _sessionMaxNavigationDepth = message.Depth;
+        }
+    }
+
+    public void Receive(SearchQueryMessage message)
+    {
+        _sessionSearchQueriesCount++;
+    }
+
+    public void Receive(ErrorOccurredMessage message)
+    {
+        _sessionErrorCount++;
+    }
+
+    /// <summary>
+    /// Ends the current telemetry session and emits the CmdPal_SessionDuration event.
+    /// Aggregates all session metrics collected since ShowWindow and sends them to telemetry.
+    /// </summary>
+    /// <param name="dismissalReason">The reason the session ended (e.g., Dismiss, Hide, LostFocus).</param>
+    private void EndSession(string dismissalReason)
+    {
+        if (_sessionStopwatch is not null)
+        {
+            _sessionStopwatch.Stop();
+            TelemetryForwarder.LogSessionDuration(
+                (ulong)_sessionStopwatch.ElapsedMilliseconds,
+                _sessionCommandsExecuted,
+                _sessionPagesVisited,
+                dismissalReason,
+                _sessionSearchQueriesCount,
+                _sessionMaxNavigationDepth,
+                _sessionErrorCount);
+            _sessionStopwatch = null;
+        }
+    }
+
+    /// <summary>
+    /// Increments the session commands executed counter for telemetry.
+    /// Called by TelemetryForwarder when an extension command is invoked.
+    /// </summary>
+    internal void IncrementCommandsExecuted()
+    {
+        _sessionCommandsExecuted++;
+    }
+
     private void HideWindow()
     {
         // Cloak our HWND to avoid all animations.
@@ -764,6 +843,7 @@ public sealed partial class MainWindow : WindowEx,
             }
 
             // This will DWM cloak our window:
+            EndSession("LostFocus");
             HideWindow();
 
             PowerToysTelemetry.Log.WriteEvent(new CmdPalDismissedOnLostFocus());