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/Helpers/TelemetryForwarder.cs

@@ -6,40 +6,78 @@ using CommunityToolkit.Mvvm.Messaging;
 using Microsoft.CmdPal.Core.Common.Services;
 using Microsoft.CmdPal.Core.ViewModels.Messages;
 using Microsoft.CmdPal.UI.Events;
+using Microsoft.CommandPalette.Extensions;
 using Microsoft.PowerToys.Telemetry;
 
 namespace Microsoft.CmdPal.UI;
 
 /// <summary>
 /// TelemetryForwarder is responsible for forwarding telemetry events from the
-/// command palette core to PowerToys Telemetry.
-/// This allows us to emit telemetry events as messages from the core,
-/// and then handle them by logging to our PT telemetry provider.
-///
-/// We may in the future want to replace this with a more generic "ITelemetryService"
-/// or something similar, but this works for now.
+/// command palette to PowerToys Telemetry.
+/// Listens to telemetry-specific messages from the core layer and logs them to PowerToys telemetry.
+/// Also implements ITelemetryService for dependency injection in extensions.
 /// </summary>
 internal sealed class TelemetryForwarder :
     ITelemetryService,
-    IRecipient<BeginInvokeMessage>,
-    IRecipient<CmdPalInvokeResultMessage>
+    IRecipient<TelemetryBeginInvokeMessage>,
+    IRecipient<TelemetryInvokeResultMessage>,
+    IRecipient<TelemetryExtensionInvokedMessage>
 {
     public TelemetryForwarder()
     {
-        WeakReferenceMessenger.Default.Register<BeginInvokeMessage>(this);
-        WeakReferenceMessenger.Default.Register<CmdPalInvokeResultMessage>(this);
+        WeakReferenceMessenger.Default.Register<TelemetryBeginInvokeMessage>(this);
+        WeakReferenceMessenger.Default.Register<TelemetryInvokeResultMessage>(this);
+        WeakReferenceMessenger.Default.Register<TelemetryExtensionInvokedMessage>(this);
     }
 
-    public void Receive(CmdPalInvokeResultMessage message)
-    {
-        PowerToysTelemetry.Log.WriteEvent(new CmdPalInvokeResult(message.Kind));
-    }
-
-    public void Receive(BeginInvokeMessage message)
+    // Message handlers for telemetry events from core layer
+    public void Receive(TelemetryBeginInvokeMessage message)
     {
         PowerToysTelemetry.Log.WriteEvent(new BeginInvoke());
     }
 
+    public void Receive(TelemetryInvokeResultMessage message)
+    {
+        PowerToysTelemetry.Log.WriteEvent(new CmdPalInvokeResult(message.Kind));
+    }
+
+    public void Receive(TelemetryExtensionInvokedMessage message)
+    {
+        PowerToysTelemetry.Log.WriteEvent(new CmdPalExtensionInvoked(
+            message.ExtensionId,
+            message.CommandId,
+            message.CommandName,
+            message.Success,
+            message.ExecutionTimeMs));
+
+        // Increment session counter for commands executed
+        if (App.Current.AppWindow is MainWindow mainWindow)
+        {
+            mainWindow.IncrementCommandsExecuted();
+        }
+    }
+
+    // Static method for logging session duration from UI layer
+    public static void LogSessionDuration(
+        ulong durationMs,
+        int commandsExecuted,
+        int pagesVisited,
+        string dismissalReason,
+        int searchQueriesCount,
+        int maxNavigationDepth,
+        int errorCount)
+    {
+        PowerToysTelemetry.Log.WriteEvent(new CmdPalSessionDuration(
+            durationMs,
+            commandsExecuted,
+            pagesVisited,
+            dismissalReason,
+            searchQueriesCount,
+            maxNavigationDepth,
+            errorCount));
+    }
+
+    // ITelemetryService implementation for dependency injection in extensions
     public void LogRunQuery(string query, int resultCount, ulong durationMs)
     {
         PowerToysTelemetry.Log.WriteEvent(new CmdPalRunQuery(query, resultCount, durationMs));