Address Phase 3 review: wire shapes and thread safety

- Filter separators read the SDK "separator" flag instead of "_isSeparator"
  (list-item separators still use "_isSeparator" per the SDK serializer).
- Grid layout reads the SDK "type" discriminator instead of "layout".
- fallback/updateQuery is sent as a request, matching the protocol and SDK.
- Scope listPage/itemsChanged routing per connection via a ConditionalWeakTable
  keyed by the JsonRpcConnection, holding proxies as weak references so ids from
  different extensions no longer collide and collected proxies are pruned.
- Use a ConcurrentDictionary for the fallback adapter map shared between the
  request path and the JSON-RPC reader thread.
- Add tests covering filter separators, grid type, and fallback updateQuery.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: f9b90e37-dcfc-4ea7-8a79-87eb2af072b6

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/Models/JSCommandProviderProxy.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Text.Json;
 using System.Text.Json.Nodes;
@@ -26,7 +27,7 @@ public sealed partial class JSCommandProviderProxy : ICommandProvider, IDisposab
     private readonly JSExtensionManifest _manifest;
     private readonly IconInfo _icon;
     private readonly Dictionary<(string Message, int State), StatusMessage> _shownStatusMessages = new();
-    private readonly Dictionary<string, JSFallbackCommandItemAdapter> _fallbackAdapters = new();
+    private readonly ConcurrentDictionary<string, JSFallbackCommandItemAdapter> _fallbackAdapters = new();
     private IExtensionHost? _host;
     private ICommandSettings? _settingsCache;
     private bool _settingsQueried;

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/Models/JSFallbackCommandItemAdapter.cs

@@ -98,7 +98,7 @@ internal sealed partial class JSFallbackCommandItemAdapter : BaseObservable, IFa
         {
             try
             {
-                _connection.SendNotificationAsync(
+                _connection.SendRequestAsync(
                     "fallback/updateQuery",
                     new JsonObject { ["commandId"] = _commandId, ["query"] = query },
                     CancellationToken.None).GetAwaiter().GetResult();

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/Models/JSListPageProxy.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Runtime.CompilerServices;
 using System.Text.Json;
 using System.Text.Json.Nodes;
 using System.Threading;
@@ -24,7 +25,10 @@ namespace Microsoft.CmdPal.UI.ViewModels.Models;
 /// </summary>
 internal sealed partial class JSListPageProxy : BaseObservable, IListPage
 {
-    private static readonly ConcurrentDictionary<string, JSListPageProxy> ProxyRegistry = new();
+    // Routing is scoped per connection so that identical page ids from different
+    // extensions never collide. Proxies are held weakly so they can be collected
+    // without the registry keeping them alive.
+    private static readonly ConditionalWeakTable<JsonRpcConnection, PageRegistry> Registries = new();
 
     private readonly string _pageId;
     private readonly JsonRpcConnection _connection;
@@ -36,8 +40,14 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage
         _connection = connection ?? throw new ArgumentNullException(nameof(connection));
         _pageData = pageData;
 
-        ProxyRegistry[_pageId] = this;
-        _connection.RegisterNotificationHandler("listPage/itemsChanged", DispatchItemsChanged);
+        var registry = Registries.GetValue(_connection, static conn =>
+        {
+            var created = new PageRegistry();
+            conn.RegisterNotificationHandler("listPage/itemsChanged", paramsElement => DispatchItemsChanged(created, paramsElement));
+            return created;
+        });
+
+        registry.Pages[_pageId] = new WeakReference<JSListPageProxy>(this);
     }
 
     public event TypedEventHandler<object, IItemsChangedEventArgs>? ItemsChanged;
@@ -131,7 +141,7 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage
         }
     }
 
-    private static void DispatchItemsChanged(JsonElement paramsElement)
+    private static void DispatchItemsChanged(PageRegistry registry, JsonElement paramsElement)
     {
         try
         {
@@ -142,11 +152,18 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage
             }
 
             var pageId = pageProp.GetString();
-            if (pageId == null || !ProxyRegistry.TryGetValue(pageId, out var proxy))
+            if (pageId == null || !registry.Pages.TryGetValue(pageId, out var weakProxy))
             {
                 return;
             }
 
+            if (!weakProxy.TryGetTarget(out var proxy))
+            {
+                // The proxy has been collected; drop the stale entry.
+                registry.Pages.TryRemove(pageId, out _);
+                return;
+            }
+
             var totalItems = -1;
             if (paramsElement.TryGetProperty("totalItems", out var totalItemsProp) &&
                 totalItemsProp.ValueKind == JsonValueKind.Number)
@@ -202,4 +219,9 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage
 
         return items.ToArray();
     }
+
+    private sealed class PageRegistry
+    {
+        public ConcurrentDictionary<string, WeakReference<JSListPageProxy>> Pages { get; } = new();
+    }
 }

src/modules/cmdpal/Microsoft.CmdPal.UI.ViewModels/Models/JSModelMapper.cs

@@ -291,7 +291,7 @@ internal static class JSModelMapper
             return null;
         }
 
-        var layout = GetString(gridProp, "layout") ?? string.Empty;
+        var layout = GetString(gridProp, "type") ?? string.Empty;
         var showTitle = GetBool(gridProp, "showTitle", true);
         var showSubtitle = GetBool(gridProp, "showSubtitle", true);
 
@@ -316,7 +316,7 @@ internal static class JSModelMapper
         var filters = new List<IFilterItem>();
         foreach (var element in filtersProp.EnumerateArray())
         {
-            if (GetBool(element, "_isSeparator", false))
+            if (GetBool(element, "separator", false))
             {
                 filters.Add(new Separator(GetString(element, "title") ?? string.Empty));
                 continue;

src/modules/cmdpal/Tests/Microsoft.CmdPal.UI.ViewModels.UnitTests/JSAdapterProxyTests.cs

@@ -269,6 +269,68 @@ public class JSAdapterProxyTests
         Assert.IsNotNull(settings!.SettingsPage);
     }
 
+    [TestMethod]
+    public void ListPage_ExposesFiltersWithSeparatorAndGridType()
+    {
+        using var fake = new JSFakeExtension();
+        var commandJson =
+            """
+            {
+              "id": "list-fg",
+              "pageType": "listPage",
+              "name": "Filtered",
+              "gridProperties": { "type": "medium", "showTitle": true },
+              "filters": {
+                "currentFilterId": "all",
+                "filters": [
+                  { "id": "all", "name": "All" },
+                  { "separator": true },
+                  { "id": "recent", "name": "Recent" }
+                ]
+              }
+            }
+            """;
+        fake.OnResult("provider/getCommand", commandJson);
+
+        var provider = CreateProvider(fake);
+        var page = (IListPage)provider.GetCommand("list-fg")!;
+
+        Assert.IsInstanceOfType(page.GridProperties, typeof(IMediumGridLayout));
+
+        Assert.IsNotNull(page.Filters);
+        var filters = page.Filters!.GetFilters();
+        Assert.AreEqual(3, filters.Length);
+        Assert.IsInstanceOfType(filters[0], typeof(IFilter));
+        Assert.AreEqual("all", ((IFilter)filters[0]).Id);
+        Assert.IsInstanceOfType(filters[1], typeof(ISeparatorFilterItem));
+        Assert.IsInstanceOfType(filters[2], typeof(IFilter));
+        Assert.AreEqual("recent", ((IFilter)filters[2]).Id);
+    }
+
+    [TestMethod]
+    public async Task FallbackHandler_SendsUpdateQueryAsRequest()
+    {
+        using var fake = new JSFakeExtension();
+        fake.OnResult(
+            "provider/getFallbackCommands",
+            """[ { "id": "fb-req", "displayTitle": "Initial", "title": "T" } ]""");
+
+        var received = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
+        fake.OnRequest("fallback/updateQuery", element =>
+        {
+            received.TrySetResult(element.GetProperty("query").GetString() ?? string.Empty);
+            return null;
+        });
+
+        var provider = CreateProvider(fake);
+        var fallback = provider.FallbackCommands()![0];
+
+        await Task.Run(() => fallback.FallbackHandler.UpdateQuery("typed"));
+
+        var query = await received.Task.WaitAsync(Timeout);
+        Assert.AreEqual("typed", query);
+    }
+
     private static void AssertKind(JSFakeExtension fake, IInvokableCommand invokable, string resultJson, CommandResultKind expected)
     {
         fake.OnResult("command/invoke", resultJson);