[CmdPal] Fix context menu command items (#45499)

maintainers: we talked about this at length on Teams

> Seems like adding `IExtendedAttributesProvider` onto `CommandItem` is
what broke this. I don't know why. I'm not gonna pretend to understand
the cswinrt voodoo that's causing it to pick `IEAP` as the leaf
interface instead of `ICommandContextItem`.
 
 
drive by: fix the sample project on ARM

_resurrected from #45329 because spellbot killed that PR_

src/modules/cmdpal/ext/SamplePagesExtension/Program.cs

@@ -1,10 +1,12 @@
-// Copyright (c) Microsoft Corporation
+// Copyright (c) Microsoft Corporation
 // 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;
 using System.Threading;
 using Microsoft.CommandPalette.Extensions;
+using Shmuelie.WinRTServer;
+using Shmuelie.WinRTServer.CsWinRT;
 
 namespace SamplePagesExtension;
 
@@ -15,18 +17,22 @@ public class Program
     {
         if (args.Length > 0 && args[0] == "-RegisterProcessAsComServer")
         {
-            using ExtensionServer server = new();
+            global::Shmuelie.WinRTServer.ComServer server = new();
-            var extensionDisposedEvent = new ManualResetEvent(false);
+
-            var extensionInstance = new SampleExtension(extensionDisposedEvent);
+            ManualResetEvent extensionDisposedEvent = new(false);
 
             // We are instantiating an extension instance once above, and returning it every time the callback in RegisterExtension below is called.
             // This makes sure that only one instance of SampleExtension is alive, which is returned every time the host asks for the IExtension object.
             // If you want to instantiate a new instance each time the host asks, create the new instance inside the delegate.
-            server.RegisterExtension(() => extensionInstance);
+            SampleExtension extensionInstance = new(extensionDisposedEvent);
+            server.RegisterClass<SampleExtension, IExtension>(() => extensionInstance);
+            server.Start();
 
             // This will make the main thread wait until the event is signalled by the extension class.
-            // Since we have a single instance of the extension object, we exit as soon as it is disposed.
+            // Since we have single instance of the extension object, we exit as soon as it is disposed.
             extensionDisposedEvent.WaitOne();
+            server.Stop();
+            server.UnsafeDispose();
         }
         else
         {

src/modules/cmdpal/ext/SamplePagesExtension/SamplePagesExtension.csproj

@@ -34,6 +34,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <PackageReference Include="Shmuelie.WinRTServer" />
     <PackageReference Include="Microsoft.WindowsAppSDK" />
     <PackageReference Include="Microsoft.Windows.CsWin32">
       <PrivateAssets>all</PrivateAssets>

src/modules/cmdpal/extensionsdk/Microsoft.CommandPalette.Extensions.Toolkit/CommandItem.cs

@@ -8,8 +8,14 @@ using WinRT;
 
 namespace Microsoft.CommandPalette.Extensions.Toolkit;
 
-public partial class CommandItem : BaseObservable, ICommandItem, IExtendedAttributesProvider
+public partial class CommandItem : BaseObservable, ICommandItem
 {
+    // NOTE TO MAINTAINERS: Do NOT implement `IExtendedAttributesProvider` here
+    // directly. Instead, implement it in derived classes like `ListItem` where
+    // appropriate.
+    //
+    // Putting it directly here will cause out-of-proc extensions to fail to
+    // load the context menu commands, for unknown CsWinRT reasons.
     private readonly PropertySet _extendedAttributes = new();
 
     private ICommand? _command;

src/modules/cmdpal/extensionsdk/Microsoft.CommandPalette.Extensions.Toolkit/FallbackCommandItem.cs

@@ -1,10 +1,10 @@
-// Copyright (c) Microsoft Corporation
+// Copyright (c) Microsoft Corporation
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
 namespace Microsoft.CommandPalette.Extensions.Toolkit;
 
-public partial class FallbackCommandItem : CommandItem, IFallbackCommandItem, IFallbackHandler, IFallbackCommandItem2
+public partial class FallbackCommandItem : CommandItem, IFallbackCommandItem, IFallbackHandler, IFallbackCommandItem2, IExtendedAttributesProvider
 {
     private readonly IFallbackHandler? _fallbackHandler;
 

src/modules/cmdpal/extensionsdk/Microsoft.CommandPalette.Extensions.Toolkit/ListItem.cs

@@ -1,10 +1,10 @@
-// Copyright (c) Microsoft Corporation
+// Copyright (c) Microsoft Corporation
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
 namespace Microsoft.CommandPalette.Extensions.Toolkit;
 
-public partial class ListItem : CommandItem, IListItem
+public partial class ListItem : CommandItem, IListItem, IExtendedAttributesProvider
 {
     public virtual ITag[] Tags { get; set => SetProperty(ref field, value); } = [];