Fold gap-fix findings into adapters: prop-change bridge, fallback ID, status context, toast validation, content refresh

Consolidates 6 gap-fix branches' C# adapter/proxy changes into phase-3
so the JS/TS stack stays at 7 PRs instead of growing to 15:

- JSObservableProxyBase + IJSPropertyChangeTarget + JSPropertyChangeRegistry:
  shared property-change notification plumbing for JS-backed adapters
- JSContentPageProxy: content refresh via itemsChanged, layered on the
  new base class
- JSFallbackCommandItemAdapter, JSInvokableCommandAdapter,
  JSCommandProviderProxy, JSCommandResultParser: fallback command IDs,
  status context propagation, toast payload validation fixes
- JSStatusNotificationTests, JSAdapterProxyTests, JSAdapterRemediationTests:
  covering tests

Reconciled JSListPageProxy.cs by hand: the combined gap-fix branch was
cut from a tip that already included phase-4's ComputeKey/UpdateData
item-cache reuse logic, which isn't part of any gap fix and doesn't
exist yet on phase-3. Restored phase-3's original simple item
construction instead of carrying that unrelated phase-4 code forward.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 0fb6a401-cb0b-4f9b-b721-19987117e9e0

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

@@ -0,0 +1,12 @@
+// 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.Text.Json;
+
+namespace Microsoft.CmdPal.UI.ViewModels.Models;
+
+internal interface IJSPropertyChangeTarget
+{
+    void ApplyPropertyChanges(JsonElement properties);
+}

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

@@ -21,7 +21,7 @@ namespace Microsoft.CmdPal.UI.ViewModels.Models;
 /// provider calls over JSON-RPC. Fallback display titles, host status messages,
 /// log messages and clipboard requests raised by the extension are handled here.
 /// </summary>
-public sealed partial class JSCommandProviderProxy : ICommandProvider, IDisposable
+public sealed partial class JSCommandProviderProxy : ICommandProvider4, IDisposable
 {
     private readonly JsonRpcConnection _connection;
     private readonly JSExtensionManifest _manifest;
@@ -200,6 +200,39 @@ public sealed partial class JSCommandProviderProxy : ICommandProvider, IDisposab
         }
     }
 
+    public ICommandItem? GetCommandItem(string id)
+    {
+        try
+        {
+            var response = _connection.SendRequestAsync(
+                "provider/getCommandItem",
+                new JsonObject { ["commandId"] = id },
+                CancellationToken.None).GetAwaiter().GetResult();
+
+            if (response.Error != null)
+            {
+                Logger.LogWarning($"GetCommandItem error for {id}: {response.Error.Message}");
+                return null;
+            }
+
+            if (!response.Result.HasValue || response.Result.Value.ValueKind != JsonValueKind.Object)
+            {
+                return null;
+            }
+
+            return new JSCommandItemAdapter(response.Result.Value, _connection);
+        }
+        catch (Exception ex)
+        {
+            Logger.LogWarning($"Failed to get command item {id}: {ex.Message}");
+            return null;
+        }
+    }
+
+    public object[] GetApiExtensionStubs() => [];
+
+    public ICommandItem[]? GetDockBands() => null;
+
     public void InitializeWithHost(IExtensionHost host)
     {
         ArgumentNullException.ThrowIfNull(host);
@@ -369,6 +402,8 @@ public sealed partial class JSCommandProviderProxy : ICommandProvider, IDisposab
 
         try
         {
+            JSPropertyChangeRegistry.Dispatch(_connection, paramsElement);
+
             var commandId = JSModelMapper.GetString(paramsElement, "commandId") ?? string.Empty;
             if (string.IsNullOrEmpty(commandId) ||
                 !_fallbackAdapters.TryGetValue(commandId, out var fallbackAdapter))
@@ -716,9 +751,14 @@ public sealed partial class JSCommandProviderProxy : ICommandProvider, IDisposab
                 return (StatusContext)contextProp.GetInt32();
             }
 
-            if (contextProp.ValueKind == JsonValueKind.String && contextProp.GetString() == "page")
+            if (contextProp.ValueKind == JsonValueKind.String)
             {
-                return StatusContext.Page;
+                return contextProp.GetString() switch
+                {
+                    "page" => StatusContext.Page,
+                    "extension" => StatusContext.Extension,
+                    _ => StatusContext.Extension,
+                };
             }
         }
 

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

@@ -94,6 +94,23 @@ internal static class JSCommandResultParser
 
         var toastArgs = new ToastArgs { Message = message };
 
+        if (args.ValueKind == JsonValueKind.Object &&
+            JSModelMapper.TryGetAnyCase(args, "icon", "Icon", out var iconProp))
+        {
+            toastArgs.Icon = JSModelMapper.ParseIconInfo(iconProp);
+        }
+
+        // Action commands require the live connection used by the command
+        // adapter. If parsing is used without one, keep the toast usable and
+        // omit only the unavailable action.
+        if (connection != null &&
+            args.ValueKind == JsonValueKind.Object &&
+            JSModelMapper.TryGetAnyCase(args, "command", "Command", out var commandProp) &&
+            commandProp.ValueKind == JsonValueKind.Object)
+        {
+            toastArgs.Command = JSCommandFactory.CreateCommandFromJson(commandProp, connection);
+        }
+
         // A toast can carry a nested continuation result that the shell executes
         // after the toast is shown. Parse it recursively so every nested kind
         // (including confirm, which needs the connection for its primary command,

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

@@ -3,9 +3,13 @@
 // See the LICENSE file in the project root for more information.
 
 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;
+using System.Threading.Tasks;
 using ManagedCommon;
 using Microsoft.CmdPal.UI.ViewModels.Services.JsonRpc;
 using Microsoft.CommandPalette.Extensions;
@@ -19,46 +23,51 @@ namespace Microsoft.CmdPal.UI.ViewModels.Models;
 /// Content is fetched with <c>contentPage/getContent</c>; details and commands are
 /// materialized from the page payload.
 /// </summary>
-internal sealed partial class JSContentPageProxy : BaseObservable, IContentPage
+internal sealed partial class JSContentPageProxy : JSObservableProxyBase, IContentPage
 {
+    private static readonly ConditionalWeakTable<JsonRpcConnection, PageRegistry> Registries = new();
+
     private readonly string _pageId;
-    private readonly JsonRpcConnection _connection;
-    private readonly JsonElement _pageData;
+    private readonly PageRegistry _registry;
 
     public JSContentPageProxy(string pageId, JsonRpcConnection connection, JsonElement pageData = default)
+        : base(pageId, connection, pageData)
     {
         _pageId = pageId ?? throw new ArgumentNullException(nameof(pageId));
-        _connection = connection ?? throw new ArgumentNullException(nameof(connection));
-        _pageData = pageData;
+
+        _registry = Registries.GetValue(Connection, static _ => new PageRegistry());
+        _registry.EnsureSubscribed(Connection);
+
+        var pages = _registry.Pages.GetOrAdd(_pageId, static _ => new List<WeakReference<JSContentPageProxy>>());
+        lock (pages)
+        {
+            pages.Add(new WeakReference<JSContentPageProxy>(this));
+        }
     }
 
-    public event TypedEventHandler<object, IItemsChangedEventArgs>? ItemsChanged
-    {
-        add { }
-        remove { }
-    }
+    public event TypedEventHandler<object, IItemsChangedEventArgs>? ItemsChanged;
 
-    public string Id => JSModelMapper.GetString(_pageData, "id") ?? _pageId;
+    public string Id => JSModelMapper.GetString(Data, "id") ?? _pageId;
 
-    public string Name => JSModelMapper.GetString(_pageData, "name") ?? string.Empty;
+    public string Name => JSModelMapper.GetString(Data, "name") ?? string.Empty;
 
-    public IIconInfo Icon => JSModelMapper.GetIcon(_pageData, "icon", "Icon");
+    public IIconInfo Icon => JSModelMapper.GetIcon(Data, "icon", "Icon");
 
-    public string Title => JSModelMapper.GetString(_pageData, "title") ?? Name;
+    public string Title => JSModelMapper.GetString(Data, "title") ?? Name;
 
-    public bool IsLoading => JSModelMapper.GetBool(_pageData, "isLoading", false);
+    public bool IsLoading => JSModelMapper.GetBool(Data, "isLoading", false);
 
-    public OptionalColor AccentColor => JSModelMapper.ParseColor(_pageData, "accentColor", "AccentColor");
+    public OptionalColor AccentColor => JSModelMapper.ParseColor(Data, "accentColor", "AccentColor");
 
-    public IDetails? Details => JSModelMapper.ParseDetails(_pageData, _connection);
+    public IDetails? Details => JSModelMapper.ParseDetails(Data, Connection);
 
-    public IContextItem[] Commands => JSModelMapper.ParseContextItems(_pageData, "commands", "Commands", _connection);
+    public IContextItem[] Commands => JSModelMapper.ParseContextItems(Data, "commands", "Commands", Connection);
 
     public IContent[] GetContent()
     {
         try
         {
-            var response = _connection.SendRequestAsync(
+            var response = Connection.SendRequestAsync(
                 "contentPage/getContent",
                 new JsonObject { ["pageId"] = _pageId },
                 CancellationToken.None).GetAwaiter().GetResult();
@@ -69,7 +78,7 @@ internal sealed partial class JSContentPageProxy : BaseObservable, IContentPage
                 return [];
             }
 
-            return JSModelMapper.ParseContentArray(UnwrapContent(response.Result), _pageId, _connection);
+            return JSModelMapper.ParseContentArray(UnwrapContent(response.Result), _pageId, Connection);
         }
         catch (Exception ex)
         {
@@ -78,6 +87,30 @@ internal sealed partial class JSContentPageProxy : BaseObservable, IContentPage
         }
     }
 
+    public override void Dispose()
+    {
+        if (_registry.Pages.TryGetValue(_pageId, out var pages))
+        {
+            lock (pages)
+            {
+                pages.RemoveAll(weak => !weak.TryGetTarget(out var target) || ReferenceEquals(target, this));
+                if (pages.Count == 0)
+                {
+                    _registry.Pages.TryRemove(_pageId, out _);
+                }
+            }
+        }
+
+        base.Dispose();
+    }
+
+    protected override bool SupportsProperty(string propertyName) => propertyName switch
+    {
+        "id" or "name" or "icon" or "title" or "isLoading" or "accentColor" or
+        "details" or "commands" => true,
+        _ => false,
+    };
+
     private static JsonElement? UnwrapContent(JsonElement? result)
     {
         if (!result.HasValue)
@@ -93,4 +126,77 @@ internal sealed partial class JSContentPageProxy : BaseObservable, IContentPage
 
         return result;
     }
+
+    private static void DispatchItemsChanged(PageRegistry registry, JsonElement parameters)
+    {
+        try
+        {
+            if (parameters.ValueKind != JsonValueKind.Object ||
+                !parameters.TryGetProperty("pageId", out var pageProperty))
+            {
+                return;
+            }
+
+            var pageId = pageProperty.GetString();
+            if (pageId is null || !registry.Pages.TryGetValue(pageId, out var pageReferences))
+            {
+                return;
+            }
+
+            List<JSContentPageProxy> targets = [];
+            lock (pageReferences)
+            {
+                pageReferences.RemoveAll(weak => !weak.TryGetTarget(out _));
+                foreach (var weak in pageReferences)
+                {
+                    if (weak.TryGetTarget(out var target))
+                    {
+                        targets.Add(target);
+                    }
+                }
+
+                if (pageReferences.Count == 0)
+                {
+                    registry.Pages.TryRemove(pageId, out _);
+                }
+            }
+
+            foreach (var target in targets)
+            {
+                var handler = target.ItemsChanged;
+                if (handler is not null)
+                {
+                    _ = Task.Run(() => handler.Invoke(target, new ItemsChangedEventArgs(-1)));
+                }
+            }
+        }
+        catch (Exception ex)
+        {
+            Logger.LogWarning($"Error handling contentPage/itemsChanged notification: {ex.Message}");
+        }
+    }
+
+    private sealed class PageRegistry
+    {
+        private readonly object _subscribeLock = new();
+        private bool _subscribed;
+
+        public ConcurrentDictionary<string, List<WeakReference<JSContentPageProxy>>> Pages { get; } = new();
+
+        public void EnsureSubscribed(JsonRpcConnection connection)
+        {
+            lock (_subscribeLock)
+            {
+                if (_subscribed)
+                {
+                    return;
+                }
+
+                connection.RegisterNotificationHandler(
+                    "contentPage/itemsChanged",
+                    parameters => DispatchItemsChanged(this, parameters));
+                _subscribed = true;
+            }
+        }
+    }
 }

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

@@ -68,13 +68,13 @@ internal sealed partial class JSFallbackCommandItemAdapter : BaseObservable, IFa
 
     public string DisplayTitle => _displayTitleOverride ?? JSModelMapper.GetString(_data, "displayTitle") ?? Title;
 
-    public string Id => JSModelMapper.GetString(_data, "id") ?? string.Empty;
+    public string Id => JSModelMapper.GetString(_data, "id") ?? Command?.Id ?? string.Empty;
 
     public IFallbackHandler FallbackHandler
     {
         get
         {
-            _fallbackHandler ??= new JSFallbackHandler(_connection, Id);
+            _fallbackHandler ??= new JSFallbackHandler(_connection, Command?.Id ?? Id);
             return _fallbackHandler;
         }
     }

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

@@ -18,28 +18,24 @@ namespace Microsoft.CmdPal.UI.ViewModels.Models;
 /// <see cref="IInvokableCommand"/>. Invoking sends a <c>command/invoke</c>
 /// request and maps the response to a toolkit command result.
 /// </summary>
-internal sealed partial class JSInvokableCommandAdapter : BaseObservable, IInvokableCommand
+internal sealed partial class JSInvokableCommandAdapter : JSObservableProxyBase, IInvokableCommand
 {
-    private readonly JsonElement _data;
-    private readonly JsonRpcConnection _connection;
-
     public JSInvokableCommandAdapter(JsonElement data, JsonRpcConnection connection)
+        : base(JSModelMapper.GetString(data, "id") ?? string.Empty, connection, data)
     {
-        _data = data;
-        _connection = connection;
     }
 
-    public string Name => JSModelMapper.GetString(_data, "displayName") ?? JSModelMapper.GetString(_data, "name") ?? string.Empty;
+    public string Name => JSModelMapper.GetString(Data, "displayName") ?? JSModelMapper.GetString(Data, "name") ?? string.Empty;
 
-    public string Id => JSModelMapper.GetString(_data, "id") ?? string.Empty;
+    public string Id => JSModelMapper.GetString(Data, "id") ?? string.Empty;
 
-    public IIconInfo Icon => JSModelMapper.GetIcon(_data, "icon", "Icon");
+    public IIconInfo Icon => JSModelMapper.GetIcon(Data, "icon", "Icon");
 
     public ICommandResult Invoke(object? sender)
     {
         try
         {
-            var response = _connection.SendRequestAsync(
+            var response = Connection.SendRequestAsync(
                 "command/invoke",
                 new JsonObject { ["commandId"] = Id },
                 CancellationToken.None).GetAwaiter().GetResult();
@@ -50,7 +46,7 @@ internal sealed partial class JSInvokableCommandAdapter : BaseObservable, IInvok
                 return CommandResult.KeepOpen();
             }
 
-            return JSCommandResultParser.ParseCommandResult(response.Result, _connection);
+            return JSCommandResultParser.ParseCommandResult(response.Result, Connection);
         }
         catch (Exception ex)
         {
@@ -60,4 +56,10 @@ internal sealed partial class JSInvokableCommandAdapter : BaseObservable, IInvok
     }
 
     public ICommandResult Invoke() => Invoke(this);
+
+    protected override bool SupportsProperty(string propertyName) => propertyName switch
+    {
+        "id" or "name" or "icon" => true,
+        _ => false,
+    };
 }

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.Linq;
 using System.Runtime.CompilerServices;
 using System.Text.Json;
 using System.Text.Json.Nodes;
@@ -23,7 +24,7 @@ namespace Microsoft.CmdPal.UI.ViewModels.Models;
 /// Items are fetched with <c>listPage/getItems</c> and the extension can push
 /// <c>listPage/itemsChanged</c> notifications to refresh the view.
 /// </summary>
-internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisposable
+internal sealed partial class JSListPageProxy : JSObservableProxyBase, IListPage
 {
     // Routing is scoped per connection so that identical page ids from different
     // extensions never collide. Each page id maps to the set of live proxies that
@@ -34,18 +35,15 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
     private static readonly ConditionalWeakTable<JsonRpcConnection, PageRegistry> Registries = new();
 
     private readonly string _pageId;
-    private readonly JsonRpcConnection _connection;
-    private readonly JsonElement _pageData;
     private readonly PageRegistry _registry;
     private readonly object _stateLock = new();
     private bool? _hasMoreItemsState;
     private bool _disposed;
 
     public JSListPageProxy(string pageId, JsonRpcConnection connection, JsonElement pageData = default)
+        : base(pageId, connection, pageData)
     {
         _pageId = pageId ?? throw new ArgumentNullException(nameof(pageId));
-        _connection = connection ?? throw new ArgumentNullException(nameof(connection));
-        _pageData = pageData;
 
         // Establish the retained registry first. The factory must stay free of
         // side effects: ConditionalWeakTable can invoke it on a thread that then
@@ -54,8 +52,8 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
         // that is thrown away while proxies register into a different one. The
         // handler is wired exactly once below, against the registry actually
         // retained.
-        _registry = Registries.GetValue(_connection, static _ => new PageRegistry());
-        _registry.EnsureSubscribed(_connection);
+        _registry = Registries.GetValue(Connection, static _ => new PageRegistry());
+        _registry.EnsureSubscribed(Connection);
 
         var list = _registry.Pages.GetOrAdd(_pageId, static _ => new List<WeakReference<JSListPageProxy>>());
         lock (list)
@@ -68,37 +66,37 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
 
     public string Id => _pageId;
 
-    public string Name => JSModelMapper.GetString(_pageData, "name") ?? string.Empty;
+    public string Name => JSModelMapper.GetString(Data, "name") ?? string.Empty;
 
-    public IIconInfo Icon => JSModelMapper.GetIcon(_pageData, "icon", "Icon");
+    public IIconInfo Icon => JSModelMapper.GetIcon(Data, "icon", "Icon");
 
-    public string Title => JSModelMapper.GetString(_pageData, "title") ?? Name;
+    public string Title => JSModelMapper.GetString(Data, "title") ?? Name;
 
-    public bool IsLoading => JSModelMapper.GetBool(_pageData, "isLoading", false);
+    public bool IsLoading => JSModelMapper.GetBool(Data, "isLoading", false);
 
-    public OptionalColor AccentColor => JSModelMapper.ParseColor(_pageData, "accentColor", "AccentColor");
+    public OptionalColor AccentColor => JSModelMapper.ParseColor(Data, "accentColor", "AccentColor");
 
-    public string SearchText => JSModelMapper.GetString(_pageData, "searchText") ?? string.Empty;
+    public string SearchText => JSModelMapper.GetString(Data, "searchText") ?? string.Empty;
 
-    public string PlaceholderText => JSModelMapper.GetString(_pageData, "placeholderText") ?? string.Empty;
+    public string PlaceholderText => JSModelMapper.GetString(Data, "placeholderText") ?? string.Empty;
 
-    public bool ShowDetails => JSModelMapper.GetBool(_pageData, "showDetails", false);
+    public bool ShowDetails => JSModelMapper.GetBool(Data, "showDetails", false);
 
     public IFilters? Filters
     {
         get
         {
-            if (JSModelMapper.TryGetAnyCase(_pageData, "filters", "Filters", out var filtersProp) &&
+            if (JSModelMapper.TryGetAnyCase(Data, "filters", "Filters", out var filtersProp) &&
                 filtersProp.ValueKind == JsonValueKind.Object)
             {
-                return new JSFiltersAdapter(filtersProp, _connection, _pageId);
+                return new JSFiltersAdapter(filtersProp, Connection, _pageId);
             }
 
             return null;
         }
     }
 
-    public IGridProperties? GridProperties => JSModelMapper.ParseGridProperties(_pageData);
+    public IGridProperties? GridProperties => JSModelMapper.ParseGridProperties(Data);
 
     // Pagination state is mutable: the extension reports whether more pages
     // remain via the getItems / loadMore responses and itemsChanged
@@ -110,7 +108,7 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
         {
             lock (_stateLock)
             {
-                return _hasMoreItemsState ?? JSModelMapper.GetBool(_pageData, "hasMoreItems", false);
+                return _hasMoreItemsState ?? JSModelMapper.GetBool(Data, "hasMoreItems", false);
             }
         }
     }
@@ -119,10 +117,10 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
     {
         get
         {
-            if (JSModelMapper.TryGetAnyCase(_pageData, "emptyContent", "EmptyContent", out var emptyProp) &&
+            if (JSModelMapper.TryGetAnyCase(Data, "emptyContent", "EmptyContent", out var emptyProp) &&
                 emptyProp.ValueKind == JsonValueKind.Object)
             {
-                return new JSCommandItemAdapter(emptyProp, _connection);
+                return new JSCommandItemAdapter(emptyProp, Connection);
             }
 
             return null;
@@ -133,7 +131,7 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
     {
         try
         {
-            var response = _connection.SendRequestAsync(
+            var response = Connection.SendRequestAsync(
                 "listPage/getItems",
                 new JsonObject { ["pageId"] = _pageId },
                 CancellationToken.None).GetAwaiter().GetResult();
@@ -167,7 +165,7 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
 
         try
         {
-            var response = _connection.SendRequestAsync(
+            var response = Connection.SendRequestAsync(
                 "listPage/loadMore",
                 new JsonObject { ["pageId"] = _pageId },
                 CancellationToken.None).GetAwaiter().GetResult();
@@ -316,7 +314,7 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
         ItemsChanged?.Invoke(this, new ItemsChangedEventArgs(totalItems));
     }
 
-    public void Dispose()
+    public override void Dispose()
     {
         if (_disposed)
         {
@@ -325,6 +323,8 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
 
         _disposed = true;
 
+        base.Dispose();
+
         if (_registry.Pages.TryGetValue(_pageId, out var list))
         {
             lock (list)
@@ -399,6 +399,28 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
         }
     }
 
+    protected override bool SupportsProperty(string propertyName) => propertyName switch
+    {
+        "id" or "name" or "icon" or "title" or "isLoading" or "accentColor" or
+        "searchText" or "placeholderText" or "showDetails" or "filters" or
+        "gridProperties" or "hasMoreItems" or "emptyContent" => true,
+        _ => false,
+    };
+
+    protected override void OnPropertyChangesApplied(IReadOnlyList<string> propertyNames)
+    {
+        if (!propertyNames.Contains("hasMoreItems"))
+        {
+            return;
+        }
+
+        var value = JSModelMapper.GetBool(Data, "hasMoreItems", false);
+        lock (_stateLock)
+        {
+            _hasMoreItemsState = value;
+        }
+    }
+
     private IListItem[] ParseListItems(JsonElement? result)
     {
         if (!result.HasValue)
@@ -428,7 +450,7 @@ internal sealed partial class JSListPageProxy : BaseObservable, IListPage, IDisp
             }
             else
             {
-                items.Add(new JSListItemAdapter(element, _connection));
+                items.Add(new JSListItemAdapter(element, Connection));
             }
         }
 

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

@@ -0,0 +1,106 @@
+// 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.Collections.Generic;
+using System.Text.Json;
+using System.Text.Json.Nodes;
+using System.Threading;
+using ManagedCommon;
+using Microsoft.CmdPal.UI.ViewModels.Services.JsonRpc;
+using Microsoft.CommandPalette.Extensions.Toolkit;
+
+namespace Microsoft.CmdPal.UI.ViewModels.Models;
+
+internal abstract class JSObservableProxyBase : BaseObservable, IJSPropertyChangeTarget, IDisposable
+{
+    private readonly string _commandId;
+    private readonly JsonRpcConnection _connection;
+    private DataBox _data;
+    private bool _disposed;
+
+    protected JSObservableProxyBase(string commandId, JsonRpcConnection connection, JsonElement data)
+    {
+        _commandId = commandId ?? throw new ArgumentNullException(nameof(commandId));
+        _connection = connection ?? throw new ArgumentNullException(nameof(connection));
+        _data = new DataBox(data);
+        JSPropertyChangeRegistry.Register(connection, commandId, this);
+    }
+
+    protected JsonRpcConnection Connection => _connection;
+
+    protected JsonElement Data => Volatile.Read(ref _data).Element;
+
+    protected abstract bool SupportsProperty(string propertyName);
+
+    public void ApplyPropertyChanges(JsonElement properties)
+    {
+        var current = Data;
+        if (current.ValueKind != JsonValueKind.Object)
+        {
+            return;
+        }
+
+        var changed = new List<string>();
+        var merged = JsonNode.Parse(current.GetRawText()) as JsonObject;
+        if (merged is null)
+        {
+            return;
+        }
+
+        foreach (var property in properties.EnumerateObject())
+        {
+            if (!SupportsProperty(property.Name))
+            {
+                continue;
+            }
+
+            merged[property.Name] = JsonNode.Parse(property.Value.GetRawText());
+            changed.Add(property.Name);
+        }
+
+        if (changed.Count == 0)
+        {
+            return;
+        }
+
+        using var document = JsonDocument.Parse(merged.ToJsonString());
+        Volatile.Write(ref _data, new DataBox(document.RootElement.Clone()));
+        OnPropertyChangesApplied(changed);
+
+        foreach (var property in changed)
+        {
+            OnPropertyChanged(ToAbiPropertyName(property));
+        }
+    }
+
+    protected virtual void OnPropertyChangesApplied(IReadOnlyList<string> propertyNames)
+    {
+    }
+
+    public virtual void Dispose()
+    {
+        if (_disposed)
+        {
+            return;
+        }
+
+        _disposed = true;
+        JSPropertyChangeRegistry.Unregister(_connection, _commandId, this);
+    }
+
+    private static string ToAbiPropertyName(string propertyName)
+    {
+        return propertyName.Length == 0
+            ? propertyName
+            : char.ToUpperInvariant(propertyName[0]) + propertyName[1..];
+    }
+
+    private sealed class DataBox
+    {
+        internal DataBox(JsonElement element) => Element = element;
+
+        internal JsonElement Element { get; }
+    }
+}

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

@@ -0,0 +1,88 @@
+// 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.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+using System.Text.Json;
+using Microsoft.CmdPal.UI.ViewModels.Services.JsonRpc;
+
+namespace Microsoft.CmdPal.UI.ViewModels.Models;
+
+internal static class JSPropertyChangeRegistry
+{
+    private static readonly ConditionalWeakTable<JsonRpcConnection, Registry> Registries = new();
+
+    internal static void Register(JsonRpcConnection connection, string commandId, IJSPropertyChangeTarget target)
+    {
+        var registry = Registries.GetValue(connection, static _ => new Registry());
+        var targets = registry.Targets.GetOrAdd(commandId, static _ => []);
+        lock (targets)
+        {
+            targets.Add(new WeakReference<IJSPropertyChangeTarget>(target));
+        }
+    }
+
+    internal static void Unregister(JsonRpcConnection connection, string commandId, IJSPropertyChangeTarget target)
+    {
+        if (!Registries.TryGetValue(connection, out var registry) ||
+            !registry.Targets.TryGetValue(commandId, out var targets))
+        {
+            return;
+        }
+
+        lock (targets)
+        {
+            targets.RemoveAll(reference =>
+                !reference.TryGetTarget(out var current) || ReferenceEquals(current, target));
+            if (targets.Count == 0)
+            {
+                registry.Targets.TryRemove(commandId, out _);
+            }
+        }
+    }
+
+    internal static void Dispatch(JsonRpcConnection connection, JsonElement paramsElement)
+    {
+        if (paramsElement.ValueKind != JsonValueKind.Object ||
+            !paramsElement.TryGetProperty("commandId", out var commandIdProperty) ||
+            commandIdProperty.ValueKind != JsonValueKind.String ||
+            !paramsElement.TryGetProperty("properties", out var properties) ||
+            properties.ValueKind != JsonValueKind.Object ||
+            !Registries.TryGetValue(connection, out var registry))
+        {
+            return;
+        }
+
+        var commandId = commandIdProperty.GetString();
+        if (commandId is null || !registry.Targets.TryGetValue(commandId, out var targets))
+        {
+            return;
+        }
+
+        List<IJSPropertyChangeTarget> liveTargets = [];
+        lock (targets)
+        {
+            targets.RemoveAll(reference => !reference.TryGetTarget(out _));
+            foreach (var reference in targets)
+            {
+                if (reference.TryGetTarget(out var target))
+                {
+                    liveTargets.Add(target);
+                }
+            }
+        }
+
+        foreach (var target in liveTargets)
+        {
+            target.ApplyPropertyChanges(properties);
+        }
+    }
+
+    private sealed class Registry
+    {
+        internal ConcurrentDictionary<string, List<WeakReference<IJSPropertyChangeTarget>>> Targets { get; } = new();
+    }
+}

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

@@ -86,10 +86,16 @@ public class JSAdapterProxyTests
         Assert.AreEqual(CommandResultKind.GoToPage, goToPage.Kind);
         Assert.AreEqual("target-page", ((IGoToPageArgs)goToPage.Args).PageId);
 
-        fake.OnResult("command/invoke", """{ "Kind": 6, "Args": { "message": "toasted" } }""");
+        fake.OnResult(
+            "command/invoke",
+            """{ "Kind": 6, "Args": { "message": "toasted", "icon": { "light": { "icon": "\uE700" } }, "command": { "id": "undo", "name": "Undo" } } }""");
         var toast = invokable.Invoke(null);
         Assert.AreEqual(CommandResultKind.ShowToast, toast.Kind);
         Assert.AreEqual("toasted", ((IToastArgs)toast.Args).Message);
+        var toastArgs2 = (IToastArgs2)toast.Args;
+        Assert.AreEqual("\uE700", toastArgs2.Icon.Light.Icon);
+        Assert.AreEqual("undo", toastArgs2.Command.Id);
+        Assert.AreEqual("Undo", toastArgs2.Command.Name);
 
         fake.OnResult("command/invoke", """{ "Kind": 7, "Args": { "title": "Are you sure?" } }""");
         var confirm = invokable.Invoke(null);
@@ -97,6 +103,25 @@ public class JSAdapterProxyTests
         Assert.AreEqual("Are you sure?", ((IConfirmationArgs)confirm.Args).Title);
     }
 
+    [TestMethod]
+    public void GetCommandItem_MapsFullCommandItem()
+    {
+        using var fake = new JSFakeExtension();
+        fake.OnResult(
+            "provider/getCommandItem",
+            """{ "id": "pinned", "title": "Pinned", "subtitle": "From anywhere", "command": { "id": "pinned", "name": "Pinned" }, "moreCommands": [] }""");
+
+        var provider = CreateProvider(fake);
+        var item = ((ICommandProvider4)provider).GetCommandItem("pinned");
+
+        Assert.IsNotNull(item);
+        Assert.AreEqual("Pinned", item.Title);
+        Assert.AreEqual("From anywhere", item.Subtitle);
+        Assert.IsNotNull(item.Command);
+        Assert.AreEqual("pinned", item.Command.Id);
+        Assert.AreEqual("Pinned", item.Command.Name);
+    }
+
     [TestMethod]
     public void ListPage_MapsItemsTagsDetailsSectionsSeparatorsAndMoreCommands()
     {
@@ -267,6 +292,34 @@ public class JSAdapterProxyTests
         Assert.AreEqual(CommandResultKind.Hide, submitResult.Kind);
     }
 
+    [TestMethod]
+    public async Task ContentPage_NotificationRaisesItemsChangedAndRefreshesContent()
+    {
+        using var fake = new JSFakeExtension();
+        fake.OnResult("provider/getCommand", """{ "id": "content-refresh", "pageType": "contentPage", "name": "Content" }""");
+
+        var contentBody = "initial";
+        fake.OnRequest("contentPage/getContent", _ => new JsonArray(
+            new JsonObject { ["type"] = "plainText", ["text"] = contentBody }));
+
+        var provider = CreateProvider(fake);
+        var page = (IContentPage)provider.GetCommand("content-refresh")!;
+        var initial = (IPlainTextContent)page.GetContent()[0];
+        Assert.AreEqual("initial", initial.Text);
+
+        var raised = new TaskCompletionSource<int>(TaskCreationOptions.RunContinuationsAsynchronously);
+        page.ItemsChanged += (_, args) => raised.TrySetResult(args.TotalItems);
+
+        contentBody = "updated";
+        await fake.PushNotificationAsync(
+            "contentPage/itemsChanged",
+            new JsonObject { ["pageId"] = "content-refresh" });
+
+        Assert.AreEqual(-1, await raised.Task.WaitAsync(TimeSpan.FromSeconds(10)));
+        var refreshed = (IPlainTextContent)page.GetContent()[0];
+        Assert.AreEqual("updated", refreshed.Text);
+    }
+
     [TestMethod]
     public async Task FallbackCommands_UpdateDisplayTitleOnPropChanged()
     {
@@ -362,22 +415,56 @@ public class JSAdapterProxyTests
         using var fake = new JSFakeExtension();
         fake.OnResult(
             "provider/getFallbackCommands",
-            """[ { "id": "fb-req", "displayTitle": "Initial", "title": "T" } ]""");
+            """[ { "id": "fallback-item", "displayTitle": "Initial", "title": "T", "command": { "id": "fallback-command", "name": "T" } } ]""");
 
         var received = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
         fake.OnRequest("fallback/updateQuery", element =>
         {
-            received.TrySetResult(element.GetProperty("query").GetString() ?? string.Empty);
+            received.TrySetResult(
+                $"{element.GetProperty("commandId").GetString()}|{element.GetProperty("query").GetString()}");
             return null;
         });
 
         var provider = CreateProvider(fake);
         var fallback = provider.FallbackCommands()![0];
 
+        Assert.IsInstanceOfType(fallback, typeof(IFallbackCommandItem2));
+        Assert.AreEqual("fallback-item", ((IFallbackCommandItem2)fallback).Id);
+
         await Task.Run(() => fallback.FallbackHandler.UpdateQuery("typed"));
 
-        var query = await received.Task.WaitAsync(Timeout);
-        Assert.AreEqual("typed", query);
+        var request = await received.Task.WaitAsync(Timeout);
+        Assert.AreEqual("fallback-command|typed", request);
+    }
+
+    [TestMethod]
+    public async Task CommandPropChanged_UpdatesPageStateAndRaisesAbiProperty()
+    {
+        using var fake = new JSFakeExtension();
+        fake.OnResult(
+            "provider/getCommand",
+            """{ "id": "live-page", "pageType": "listPage", "name": "Page", "title": "Old", "isLoading": false }""");
+
+        var provider = CreateProvider(fake);
+        var page = (IListPage)provider.GetCommand("live-page")!;
+        var changed = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
+        ((INotifyPropChanged)page).PropChanged += (_, args) => changed.TrySetResult(args.PropertyName);
+
+        await fake.PushNotificationAsync(
+            "command/propChanged",
+            new JsonObject
+            {
+                ["commandId"] = "live-page",
+                ["properties"] = new JsonObject
+                {
+                    ["isLoading"] = true,
+                    ["title"] = "New",
+                },
+            });
+
+        Assert.AreEqual("IsLoading", await changed.Task.WaitAsync(Timeout));
+        Assert.IsTrue(page.IsLoading);
+        Assert.AreEqual("New", page.Title);
     }
 
     private static void AssertKind(JSFakeExtension fake, IInvokableCommand invokable, string resultJson, CommandResultKind expected)

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

@@ -92,6 +92,21 @@ public partial class JSAdapterRemediationTests
         Assert.AreEqual(CommandResultKind.GoHome, toastArgs.Result!.Kind);
     }
 
+    [TestMethod]
+    public void Toast_ParsesIconAndGracefullyOmitsActionWithoutConnection()
+    {
+        using var document = JsonDocument.Parse(
+            """{ "Kind": 6, "Args": { "Message": "Saved", "Icon": { "light": { "icon": "\uE700" } }, "Command": { "id": "undo", "name": "Undo" } } }""");
+
+        var result = JSCommandResultParser.ParseCommandResult(document.RootElement, null);
+        var toastArgs = (IToastArgs2)result.Args;
+
+        Assert.AreEqual(CommandResultKind.ShowToast, result.Kind);
+        Assert.AreEqual("Saved", toastArgs.Message);
+        Assert.AreEqual("\uE700", toastArgs.Icon.Light.Icon);
+        Assert.IsNull(toastArgs.Command);
+    }
+
     // p3-03: two references to the same pageId both receive items-changed.
     [TestMethod]
     public async Task ListPage_DuplicatePageReferencesBothReceiveNotifications()

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

@@ -0,0 +1,200 @@
+// 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.Text.Json.Nodes;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CmdPal.UI.ViewModels.Models;
+using Microsoft.CommandPalette.Extensions;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Windows.Foundation;
+
+namespace Microsoft.CmdPal.UI.ViewModels.UnitTests;
+
+/// <summary>
+/// Exercises the host/showStatus notification path end to end against an in-memory
+/// fake extension, verifying that the host reads the SDK status wire shape correctly:
+/// the indeterminate progress payload and the Pascal-case State severity nested in
+/// the message object.
+/// </summary>
+[TestClass]
+public partial class JSStatusNotificationTests
+{
+    private static readonly TimeSpan Timeout = TimeSpan.FromSeconds(10);
+
+    [TestMethod]
+    public async Task ShowStatus_IndeterminateProgress_SetsProgressStateOnStatusMessage()
+    {
+        using var fake = new JSFakeExtension();
+        var provider = CreateInitializedProvider(fake, out var host);
+
+        await fake.PushNotificationAsync(
+            "host/showStatus",
+            new JsonObject
+            {
+                ["message"] = new JsonObject
+                {
+                    ["Message"] = "Working",
+                    ["State"] = 0,
+                },
+                ["progress"] = new JsonObject { ["isIndeterminate"] = true },
+                ["context"] = "extension",
+            });
+
+        var status = await host.WaitForStatusAsync();
+
+        Assert.AreEqual("Working", status.Message);
+        Assert.IsNotNull(status.Progress);
+        Assert.IsTrue(status.Progress!.IsIndeterminate);
+
+        GC.KeepAlive(provider);
+    }
+
+    [TestMethod]
+    public async Task ShowStatus_DeterminateProgress_MapsProgressPercent()
+    {
+        using var fake = new JSFakeExtension();
+        var provider = CreateInitializedProvider(fake, out var host);
+
+        await fake.PushNotificationAsync(
+            "host/showStatus",
+            new JsonObject
+            {
+                ["message"] = new JsonObject
+                {
+                    ["Message"] = "Half done",
+                    ["State"] = 0,
+                },
+                ["progress"] = new JsonObject
+                {
+                    ["isIndeterminate"] = false,
+                    ["progressPercent"] = 50,
+                },
+                ["context"] = "extension",
+            });
+
+        var status = await host.WaitForStatusAsync();
+
+        Assert.IsNotNull(status.Progress);
+        Assert.IsFalse(status.Progress!.IsIndeterminate);
+        Assert.AreEqual(50u, status.Progress.ProgressPercent);
+
+        GC.KeepAlive(provider);
+    }
+
+    [DataTestMethod]
+    [DataRow(0, MessageState.Info)]
+    [DataRow(1, MessageState.Success)]
+    [DataRow(2, MessageState.Warning)]
+    [DataRow(3, MessageState.Error)]
+    public async Task ShowStatus_PascalCaseState_MapsToSeverity(int stateValue, MessageState expected)
+    {
+        using var fake = new JSFakeExtension();
+        var provider = CreateInitializedProvider(fake, out var host);
+
+        await fake.PushNotificationAsync(
+            "host/showStatus",
+            new JsonObject
+            {
+                ["message"] = new JsonObject
+                {
+                    ["Message"] = $"State {stateValue}",
+                    ["State"] = stateValue,
+                },
+                ["context"] = "extension",
+            });
+
+        var status = await host.WaitForStatusAsync();
+
+        Assert.AreEqual(expected, status.State);
+        Assert.IsNull(status.Progress);
+
+        GC.KeepAlive(provider);
+    }
+
+    [TestMethod]
+    public async Task ShowStatus_PageContext_MapsToPageScope()
+    {
+        using var fake = new JSFakeExtension();
+        var provider = CreateInitializedProvider(fake, out var host);
+
+        await fake.PushNotificationAsync(
+            "host/showStatus",
+            new JsonObject
+            {
+                ["message"] = new JsonObject
+                {
+                    ["Message"] = "Page status",
+                    ["State"] = 0,
+                },
+                ["context"] = "page",
+            });
+
+        await host.WaitForStatusAsync();
+
+        Assert.AreEqual(StatusContext.Page, host.LastContext);
+
+        GC.KeepAlive(provider);
+    }
+
+    [TestMethod]
+    public async Task ShowStatus_OmittedContext_DefaultsToExtensionScope()
+    {
+        using var fake = new JSFakeExtension();
+        var provider = CreateInitializedProvider(fake, out var host);
+
+        await fake.PushNotificationAsync(
+            "host/showStatus",
+            new JsonObject
+            {
+                ["message"] = new JsonObject
+                {
+                    ["Message"] = "Extension status",
+                    ["State"] = 0,
+                },
+            });
+
+        await host.WaitForStatusAsync();
+
+        Assert.AreEqual(StatusContext.Extension, host.LastContext);
+
+        GC.KeepAlive(provider);
+    }
+
+    private static JSCommandProviderProxy CreateInitializedProvider(JSFakeExtension fake, out CapturingExtensionHost host)
+    {
+        host = new CapturingExtensionHost();
+        var provider = new JSCommandProviderProxy(
+            fake.Connection,
+            new JSExtensionManifest { Name = "test.ext", DisplayName = "Test Extension" });
+        provider.InitializeWithHost(host);
+        return provider;
+    }
+
+    private sealed partial class CapturingExtensionHost : IExtensionHost
+    {
+        private readonly TaskCompletionSource<IStatusMessage> _statusShown =
+            new(TaskCreationOptions.RunContinuationsAsynchronously);
+
+        public StatusContext LastContext { get; private set; } = StatusContext.Extension;
+
+        public Task<IStatusMessage> WaitForStatusAsync() => _statusShown.Task.WaitAsync(Timeout);
+
+        public IAsyncAction ShowStatus(IStatusMessage? message, StatusContext context)
+        {
+            if (message is not null)
+            {
+                LastContext = context;
+                _statusShown.TrySetResult(message);
+            }
+
+            return Task.CompletedTask.AsAsyncAction();
+        }
+
+        public IAsyncAction HideStatus(IStatusMessage? message) => Task.CompletedTask.AsAsyncAction();
+
+        public IAsyncAction LogMessage(ILogMessage? message) => Task.CompletedTask.AsAsyncAction();
+    }
+}