CmdPal: Fix Dock context menu following active item in Command Bar (#46420)

## Summary of the Pull Request

This PR decouples the Dock control context menu from the item selected
in the Shell Page list / Command Bar.

- Adds a new property to the context menu to control whether it should
react to messages like `UpdateCommandBarMessage`
- The `DockControl` context menu no longer follows those messages

Additional changes:

- Ensures the context menu for Dock-selected search box position
reflects the Dock position (when the Dock is at the bottom, the search
box is also at the bottom)
- Consistently displays the dock item context menu even for items with a
single context menu action (instead of showing the Dock menu, which was
confusing)

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## PR Checklist

- [x] Closes: #46404
- [x] Closes: #45892
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **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
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pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
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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/Microsoft.CmdPal.UI/Controls/CommandBar.xaml.cs

@@ -52,6 +52,8 @@ public sealed partial class CommandBar : UserControl,
                 return;
             }
 
+            ContextControl.PrepareForOpen(message.ContextMenuFilterLocation);
+
             _ = DispatcherQueue.TryEnqueue(
                 () =>
                 {
@@ -67,6 +69,13 @@ public sealed partial class CommandBar : UserControl,
         else
         {
             // This is invoked from a specific element
+            if (!(ContextControl.ViewModel.SelectedItem?.CanOpenContextMenu ?? false))
+            {
+                return;
+            }
+
+            ContextControl.PrepareForOpen(message.ContextMenuFilterLocation);
+
             _ = DispatcherQueue.TryEnqueue(
             () =>
             {

src/modules/cmdpal/Microsoft.CmdPal.UI/Controls/ContextMenu.xaml.cs

@@ -18,19 +18,32 @@ using Windows.System;
 namespace Microsoft.CmdPal.UI.Controls;
 
 public sealed partial class ContextMenu : UserControl,
-    IRecipient<OpenContextMenuMessage>,
     IRecipient<UpdateCommandBarMessage>,
     IRecipient<TryCommandKeybindingMessage>
 {
     public static readonly DependencyProperty ShowFilterBoxProperty =
         DependencyProperty.Register(nameof(ShowFilterBox), typeof(bool), typeof(ContextMenu), new PropertyMetadata(true));
 
+    public static readonly DependencyProperty SubscribeToCommandBarProperty =
+        DependencyProperty.Register(nameof(SubscribeToCommandBar), typeof(bool), typeof(ContextMenu), new PropertyMetadata(true, OnSubscribeToCommandBarChanged));
+
     public bool ShowFilterBox
     {
         get => (bool)GetValue(ShowFilterBoxProperty);
         set => SetValue(ShowFilterBoxProperty, value);
     }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether this control listens to the command bar's
+    /// selection and keybinding messages. Set to false for standalone usage (e.g. dock)
+    /// where the caller manages selection and opening directly.
+    /// </summary>
+    public bool SubscribeToCommandBar
+    {
+        get => (bool)GetValue(SubscribeToCommandBarProperty);
+        set => SetValue(SubscribeToCommandBarProperty, value);
+    }
+
     public ContextMenuViewModel ViewModel { get; }
 
     public ContextMenu()
@@ -40,15 +53,57 @@ public sealed partial class ContextMenu : UserControl,
         ViewModel = new ContextMenuViewModel(App.Current.Services.GetRequiredService<IFuzzyMatcherProvider>());
         ViewModel.PropertyChanged += ViewModel_PropertyChanged;
 
-        // RegisterAll isn't AOT compatible
-        WeakReferenceMessenger.Default.Register<OpenContextMenuMessage>(this);
-        WeakReferenceMessenger.Default.Register<UpdateCommandBarMessage>(this);
-        WeakReferenceMessenger.Default.Register<TryCommandKeybindingMessage>(this);
+        if (SubscribeToCommandBar)
+        {
+            HookCommandBar();
+        }
     }
 
-    public void Receive(OpenContextMenuMessage message)
+    private static void OnSubscribeToCommandBarChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
     {
-        ViewModel.FilterOnTop = message.ContextMenuFilterLocation == ContextMenuFilterLocation.Top;
+        if (d is ContextMenu control)
+        {
+            if (e.NewValue is true)
+            {
+                control.HookCommandBar();
+            }
+            else
+            {
+                control.UnhookCommandBar();
+            }
+        }
+    }
+
+    private void HookCommandBar()
+    {
+        var messenger = WeakReferenceMessenger.Default;
+
+        if (!messenger.IsRegistered<UpdateCommandBarMessage>(this))
+        {
+            messenger.Register<UpdateCommandBarMessage>(this);
+        }
+
+        if (!messenger.IsRegistered<TryCommandKeybindingMessage>(this))
+        {
+            messenger.Register<TryCommandKeybindingMessage>(this);
+        }
+
+        ViewModel.HookCommandBar();
+    }
+
+    private void UnhookCommandBar()
+    {
+        var messenger = WeakReferenceMessenger.Default;
+
+        messenger.Unregister<UpdateCommandBarMessage>(this);
+        messenger.Unregister<TryCommandKeybindingMessage>(this);
+
+        ViewModel.UnhookCommandBar();
+    }
+
+    internal void PrepareForOpen(ContextMenuFilterLocation filterLocation)
+    {
+        ViewModel.FilterOnTop = filterLocation == ContextMenuFilterLocation.Top;
         ViewModel.ResetContextMenu();
 
         UpdateUiForStackChange();

src/modules/cmdpal/Microsoft.CmdPal.UI/Dock/DockControl.xaml

@@ -103,7 +103,7 @@
                 Opened="ContextMenuFlyout_Opened"
                 ShouldConstrainToRootBounds="False"
                 SystemBackdrop="{ThemeResource AcrylicBackgroundFillColorDefaultBackdrop}">
-                <cpcontrols:ContextMenu x:Name="ContextControl" />
+                <cpcontrols:ContextMenu x:Name="ContextControl" SubscribeToCommandBar="False" />
             </Flyout>
 
             <!--  Edit mode context menu for dock bands  -->

src/modules/cmdpal/Microsoft.CmdPal.UI/Dock/DockControl.xaml.cs

@@ -7,6 +7,7 @@ using System.Collections.Specialized;
 using System.Runtime.InteropServices;
 using CommunityToolkit.Mvvm.Messaging;
 using ManagedCommon;
+using Microsoft.CmdPal.UI.Messages;
 using Microsoft.CmdPal.UI.ViewModels;
 using Microsoft.CmdPal.UI.ViewModels.Dock;
 using Microsoft.CmdPal.UI.ViewModels.Messages;
@@ -264,6 +265,13 @@ public sealed partial class DockControl : UserControl, IRecipient<CloseContextMe
         }
     }
 
+    private ContextMenuFilterLocation GetDockContextMenuFilterLocation()
+    {
+        return DockSide == DockSide.Bottom
+            ? ContextMenuFilterLocation.Bottom
+            : ContextMenuFilterLocation.Top;
+    }
+
     // Stores the band that was right-clicked for edit mode context menu
     private DockBandViewModel? _editModeContextBand;
 
@@ -297,10 +305,11 @@ public sealed partial class DockControl : UserControl, IRecipient<CloseContextMe
             }
 
             // Normal mode - show the command context menu
-            if (item.HasMoreCommands)
+            if (item.CanOpenContextMenu)
             {
                 ContextControl.ViewModel.SelectedItem = item;
                 ContextControl.ShowFilterBox = true;
+                ContextControl.PrepareForOpen(GetDockContextMenuFilterLocation());
                 PreparePopupForShow(ContextMenuFlyout, dockItem);
                 ContextMenuFlyout.ShowAt(
                     dockItem,
@@ -390,6 +399,7 @@ public sealed partial class DockControl : UserControl, IRecipient<CloseContextMe
         {
             ContextControl.ViewModel.SelectedItem = item;
             ContextControl.ShowFilterBox = false;
+            ContextControl.PrepareForOpen(GetDockContextMenuFilterLocation());
             PreparePopupForShow(ContextMenuFlyout, RootGrid);
             ContextMenuFlyout.ShowAt(
             this.RootGrid,