Fix JsonRpc proxy registration lifetimes

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 813c51f6-19e2-49ee-bf03-10e3187d3728

src/modules/cmdpal/Microsoft.CmdPal.JsonRpc/Models/JSCommandItemAdapter.cs

@@ -18,17 +18,23 @@ namespace Microsoft.CmdPal.JsonRpc.Models;
 /// </summary>
 internal sealed partial class JSCommandItemAdapter : JSObservableProxyBase, ICommandItem
 {
-    private Lazy<ICommand?> _command;
+    private readonly JSLazyCache<ICommand?> _command;
+    private readonly JSLazyCache<IContextItem[]> _moreCommands;
 
     public JSCommandItemAdapter(JsonElement data, JsonRpcConnection connection)
         : base(GetNotificationId(data), connection, data)
     {
-        _command = CreateCommand();
+        _command = new JSLazyCache<ICommand?>(
+            CreateCommand,
+            JSLazyCache<ICommand?>.DisposeValue);
+        _moreCommands = new JSLazyCache<IContextItem[]>(
+            () => JSModelMapper.ParseMoreCommands(Data, Connection),
+            JSModelMapper.DisposeContextItems);
     }
 
-    public ICommand? Command => Volatile.Read(ref _command).Value;
+    public ICommand? Command => _command.Value;
 
-    public IContextItem[] MoreCommands => JSModelMapper.ParseMoreCommands(Data, Connection);
+    public IContextItem[] MoreCommands => _moreCommands.Value;
 
     public IIconInfo Icon => JSModelMapper.TryGetIcon(Data, "icon", out var icon)
         ? icon
@@ -50,16 +56,25 @@ internal sealed partial class JSCommandItemAdapter : JSObservableProxyBase, ICom
         {
             if (propertyName == "command")
             {
-                Volatile.Write(ref _command, CreateCommand());
-                break;
+                _command.Reset();
+            }
+            else if (propertyName == "moreCommands")
+            {
+                _moreCommands.Reset();
             }
         }
     }
 
-    private Lazy<ICommand?> CreateCommand()
+    public override void Dispose()
     {
-        return new Lazy<ICommand?>(
-            () => JSCommandFactory.CreateCommandFromJson(JSModelMapper.GetCommandData(Data), Connection));
+        _moreCommands.Dispose();
+        _command.Dispose();
+        base.Dispose();
+    }
+
+    private ICommand? CreateCommand()
+    {
+        return JSCommandFactory.CreateCommandFromJson(JSModelMapper.GetCommandData(Data), Connection);
     }
 
     private static string GetNotificationId(JsonElement data)

src/modules/cmdpal/Microsoft.CmdPal.JsonRpc/Models/JSCommandProviderProxy.cs

@@ -35,6 +35,7 @@ public sealed partial class JSCommandProviderProxy : ICommandProvider4, IDisposa
     // Guards _shownStatusMessages. Host status notifications and Dispose can run
     // on different threads, so reads, writes, and enumeration share one gate.
     private readonly object _statusLock = new();
+    private readonly object _settingsLock = new();
 
     // Host notifications can arrive after this proxy subscribes but before
     // InitializeWithHost attaches the host. Buffer them in arrival order so
@@ -44,8 +45,9 @@ public sealed partial class JSCommandProviderProxy : ICommandProvider4, IDisposa
     private List<BufferedHostNotification>? _preInitNotifications = new();
     private IExtensionHost? _host;
     private ICommandSettings? _settingsCache;
+    private bool _settingsLoading;
     private bool _settingsQueried;
-    private bool _isDisposed;
+    private volatile bool _isDisposed;
 
     public JSCommandProviderProxy(
         JsonRpcConnection connection,
@@ -84,39 +86,43 @@ public sealed partial class JSCommandProviderProxy : ICommandProvider4, IDisposa
     {
         get
         {
-            if (_settingsQueried)
+            lock (_settingsLock)
             {
-                return _settingsCache;
-            }
+                while (_settingsLoading && !_isDisposed)
+                {
+                    Monitor.Wait(_settingsLock);
+                }
 
-            _settingsQueried = true;
+                if (_isDisposed)
+                {
+                    return null;
+                }
 
-            try
-            {
-                var response = _connection.SendRequestAsync(
-                    "provider/getSettings",
-                    null,
-                    CancellationToken.None).GetAwaiter().GetResult();
-
-                if (response.Error != null ||
-                    !response.Result.HasValue ||
-                    response.Result.Value.ValueKind != JsonValueKind.Object)
+                if (_settingsQueried)
                 {
                     return _settingsCache;
                 }
 
-                var pageId = JSModelMapper.GetString(response.Result.Value, "id") ?? string.Empty;
-                if (!string.IsNullOrEmpty(pageId))
-                {
-                    _settingsCache = new JSCommandSettingsProxy(pageId, _connection, response.Result.Value.Clone());
-                }
-            }
-            catch (Exception ex)
-            {
-                Logger.LogDebug($"Failed to get settings for {DisplayName}: {ex.Message}");
+                _settingsLoading = true;
             }
 
-            return _settingsCache;
+            var settings = LoadSettings();
+            lock (_settingsLock)
+            {
+                _settingsLoading = false;
+                _settingsQueried = true;
+                if (_isDisposed)
+                {
+                    (settings as IDisposable)?.Dispose();
+                }
+                else
+                {
+                    _settingsCache = settings;
+                }
+
+                Monitor.PulseAll(_settingsLock);
+                return _settingsCache;
+            }
         }
     }
 
@@ -297,6 +303,12 @@ public sealed partial class JSCommandProviderProxy : ICommandProvider4, IDisposa
             }
         }
 
+        lock (_settingsLock)
+        {
+            (_settingsCache as IDisposable)?.Dispose();
+            Monitor.PulseAll(_settingsLock);
+        }
+
         _host = null;
     }
 
@@ -320,6 +332,34 @@ public sealed partial class JSCommandProviderProxy : ICommandProvider4, IDisposa
         _connection.RegisterNotificationHandler("host/copyText", HandleCopyTextNotification);
     }
 
+    private ICommandSettings? LoadSettings()
+    {
+        try
+        {
+            var response = _connection.SendRequestAsync(
+                "provider/getSettings",
+                null,
+                CancellationToken.None).GetAwaiter().GetResult();
+
+            if (response.Error != null ||
+                !response.Result.HasValue ||
+                response.Result.Value.ValueKind != JsonValueKind.Object)
+            {
+                return null;
+            }
+
+            var pageId = JSModelMapper.GetString(response.Result.Value, "id") ?? string.Empty;
+            return string.IsNullOrEmpty(pageId)
+                ? null
+                : new JSCommandSettingsProxy(pageId, _connection, response.Result.Value.Clone());
+        }
+        catch (Exception ex)
+        {
+            Logger.LogDebug($"Failed to get settings for {DisplayName}: {ex.Message}");
+            return null;
+        }
+    }
+
     // Buffers a host notification until InitializeWithHost attaches the host.
     // The params element is cloned because the connection may recycle the source document.
     private bool TryBufferUntilHostAttached(string method, JsonElement paramsElement)

src/modules/cmdpal/Microsoft.CmdPal.JsonRpc/Models/JSCommandSettingsProxy.cs

@@ -13,18 +13,18 @@ namespace Microsoft.CmdPal.JsonRpc.Models;
 /// The full settings page payload is kept intact, including title, name, icon,
 /// details, and commands.
 /// </summary>
-internal sealed partial class JSCommandSettingsProxy : ICommandSettings
+internal sealed partial class JSCommandSettingsProxy : ICommandSettings, IDisposable
 {
-    private readonly string _settingsPageId;
-    private readonly JsonRpcConnection _connection;
-    private readonly JsonElement _settingsPageData;
+    private readonly JSLazyCache<IContentPage> _settingsPage;
 
     public JSCommandSettingsProxy(string settingsPageId, JsonRpcConnection connection, JsonElement settingsPageData = default)
     {
-        _settingsPageId = settingsPageId;
-        _connection = connection;
-        _settingsPageData = settingsPageData;
+        _settingsPage = new JSLazyCache<IContentPage>(
+            () => new JSContentPageProxy(settingsPageId, connection, settingsPageData),
+            JSLazyCache<IContentPage>.DisposeValue);
     }
 
-    public IContentPage SettingsPage => new JSContentPageProxy(_settingsPageId, _connection, _settingsPageData);
+    public IContentPage SettingsPage => _settingsPage.Value;
+
+    public void Dispose() => _settingsPage.Dispose();
 }

src/modules/cmdpal/Microsoft.CmdPal.JsonRpc/Models/JSContentPageProxy.cs

@@ -29,11 +29,19 @@ internal sealed partial class JSContentPageProxy : JSObservableProxyBase, IConte
 
     private readonly string _pageId;
     private readonly PageRegistry _registry;
+    private readonly JSLazyCache<IDetails?> _details;
+    private readonly JSLazyCache<IContextItem[]> _commands;
 
     public JSContentPageProxy(string pageId, JsonRpcConnection connection, JsonElement pageData = default)
         : base(pageId, connection, pageData)
     {
         _pageId = pageId ?? throw new ArgumentNullException(nameof(pageId));
+        _details = new JSLazyCache<IDetails?>(
+            () => JSModelMapper.ParseDetails(Data, Connection),
+            JSModelMapper.DisposeDetails);
+        _commands = new JSLazyCache<IContextItem[]>(
+            () => JSModelMapper.ParseContextItems(Data, "commands", Connection),
+            JSModelMapper.DisposeContextItems);
 
         _registry = Registries.GetValue(Connection, static _ => new PageRegistry());
         _registry.EnsureSubscribed(Connection);
@@ -59,9 +67,9 @@ internal sealed partial class JSContentPageProxy : JSObservableProxyBase, IConte
 
     public OptionalColor AccentColor => JSModelMapper.ParseColor(Data, "accentColor");
 
-    public IDetails? Details => JSModelMapper.ParseDetails(Data, Connection);
+    public IDetails? Details => _details.Value;
 
-    public IContextItem[] Commands => JSModelMapper.ParseContextItems(Data, "commands", Connection);
+    public IContextItem[] Commands => _commands.Value;
 
     public IContent[] GetContent()
     {
@@ -89,6 +97,8 @@ internal sealed partial class JSContentPageProxy : JSObservableProxyBase, IConte
 
     public override void Dispose()
     {
+        _details.Dispose();
+        _commands.Dispose();
         if (_registry.Pages.TryGetValue(_pageId, out var pages))
         {
             lock (pages)
@@ -111,6 +121,21 @@ internal sealed partial class JSContentPageProxy : JSObservableProxyBase, IConte
         _ => false,
     };
 
+    protected override void OnPropertyChangesApplied(IReadOnlyList<string> propertyNames)
+    {
+        foreach (var propertyName in propertyNames)
+        {
+            if (propertyName == "details")
+            {
+                _details.Reset();
+            }
+            else if (propertyName == "commands")
+            {
+                _commands.Reset();
+            }
+        }
+    }
+
     private static JsonElement? UnwrapContent(JsonElement? result)
     {
         if (!result.HasValue)

src/modules/cmdpal/Microsoft.CmdPal.JsonRpc/Models/JSFallbackCommandItemAdapter.cs

@@ -21,18 +21,24 @@ namespace Microsoft.CmdPal.JsonRpc.Models;
 internal sealed partial class JSFallbackCommandItemAdapter : JSObservableProxyBase, IFallbackCommandItem2
 {
     private readonly object _commandStateLock = new();
-    private Lazy<ICommand?> _command;
+    private readonly JSLazyCache<ICommand?> _command;
+    private readonly JSLazyCache<IContextItem[]> _moreCommands;
     private IFallbackHandler? _fallbackHandler;
 
     public JSFallbackCommandItemAdapter(JsonElement data, JsonRpcConnection connection)
         : base(GetNotificationId(data), connection, data)
     {
-        _command = CreateCommand();
+        _command = new JSLazyCache<ICommand?>(
+            CreateCommand,
+            JSLazyCache<ICommand?>.DisposeValue);
+        _moreCommands = new JSLazyCache<IContextItem[]>(
+            () => JSModelMapper.ParseMoreCommands(Data, Connection),
+            JSModelMapper.DisposeContextItems);
     }
 
-    public ICommand? Command => Volatile.Read(ref _command).Value;
+    public ICommand? Command => _command.Value;
 
-    public IContextItem[] MoreCommands => JSModelMapper.ParseMoreCommands(Data, Connection);
+    public IContextItem[] MoreCommands => _moreCommands.Value;
 
     public IIconInfo Icon => JSModelMapper.TryGetIcon(Data, "icon", out var icon)
         ? icon
@@ -72,19 +78,31 @@ internal sealed partial class JSFallbackCommandItemAdapter : JSObservableProxyBa
             {
                 lock (_commandStateLock)
                 {
-                    Volatile.Write(ref _command, CreateCommand());
+                    _command.Reset();
                     _fallbackHandler = null;
                 }
-
-                break;
+            }
+            else if (propertyName == "moreCommands")
+            {
+                _moreCommands.Reset();
             }
         }
     }
 
-    private Lazy<ICommand?> CreateCommand()
+    public override void Dispose()
     {
-        return new Lazy<ICommand?>(
-            () => JSCommandFactory.CreateCommandFromJson(JSModelMapper.GetCommandData(Data), Connection));
+        _moreCommands.Dispose();
+        lock (_commandStateLock)
+        {
+            _command.Dispose();
+        }
+
+        base.Dispose();
+    }
+
+    private ICommand? CreateCommand()
+    {
+        return JSCommandFactory.CreateCommandFromJson(JSModelMapper.GetCommandData(Data), Connection);
     }
 
     private static string GetNotificationId(JsonElement data)

src/modules/cmdpal/Microsoft.CmdPal.JsonRpc/Models/JSLazyCache.cs

@@ -0,0 +1,87 @@
+// 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;
+
+namespace Microsoft.CmdPal.JsonRpc.Models;
+
+internal sealed partial class JSLazyCache<T> : IDisposable
+{
+    private readonly object _lock = new();
+    private readonly Func<T> _factory;
+    private readonly Action<T>? _dispose;
+    private T _value = default!;
+    private bool _hasValue;
+    private bool _disposed;
+
+    internal JSLazyCache(Func<T> factory, Action<T>? dispose = null)
+    {
+        _factory = factory;
+        _dispose = dispose;
+    }
+
+    internal T Value
+    {
+        get
+        {
+            lock (_lock)
+            {
+                ObjectDisposedException.ThrowIf(_disposed, this);
+
+                if (!_hasValue)
+                {
+                    _value = _factory();
+                    _hasValue = true;
+                }
+
+                return _value;
+            }
+        }
+    }
+
+    public void Dispose()
+    {
+        lock (_lock)
+        {
+            if (_disposed)
+            {
+                return;
+            }
+
+            _disposed = true;
+            DisposeCreatedValue();
+        }
+    }
+
+    internal void Reset()
+    {
+        lock (_lock)
+        {
+            if (_disposed)
+            {
+                return;
+            }
+
+            DisposeCreatedValue();
+            _value = default!;
+            _hasValue = false;
+        }
+    }
+
+    internal static void DisposeValue(T value)
+    {
+        if (value is IDisposable disposable)
+        {
+            disposable.Dispose();
+        }
+    }
+
+    private void DisposeCreatedValue()
+    {
+        if (_hasValue)
+        {
+            _dispose?.Invoke(_value);
+        }
+    }
+}

src/modules/cmdpal/Microsoft.CmdPal.JsonRpc/Models/JSListItemAdapter.cs

@@ -19,17 +19,27 @@ namespace Microsoft.CmdPal.JsonRpc.Models;
 /// </summary>
 internal sealed partial class JSListItemAdapter : JSObservableProxyBase, IListItem
 {
-    private Lazy<ICommand?> _command;
+    private readonly JSLazyCache<ICommand?> _command;
+    private readonly JSLazyCache<IContextItem[]> _moreCommands;
+    private readonly JSLazyCache<IDetails?> _details;
 
     public JSListItemAdapter(JsonElement data, JsonRpcConnection connection)
         : base(GetNotificationId(data), connection, data)
     {
-        _command = CreateCommand();
+        _command = new JSLazyCache<ICommand?>(
+            CreateCommand,
+            JSLazyCache<ICommand?>.DisposeValue);
+        _moreCommands = new JSLazyCache<IContextItem[]>(
+            () => JSModelMapper.ParseMoreCommands(Data, Connection),
+            JSModelMapper.DisposeContextItems);
+        _details = new JSLazyCache<IDetails?>(
+            () => JSModelMapper.ParseDetails(Data, Connection),
+            JSModelMapper.DisposeDetails);
     }
 
-    public ICommand? Command => Volatile.Read(ref _command).Value;
+    public ICommand? Command => _command.Value;
 
-    public IContextItem[] MoreCommands => JSModelMapper.ParseMoreCommands(Data, Connection);
+    public IContextItem[] MoreCommands => _moreCommands.Value;
 
     public IIconInfo Icon => JSModelMapper.TryGetIcon(Data, "icon", out var icon)
         ? icon
@@ -41,7 +51,7 @@ internal sealed partial class JSListItemAdapter : JSObservableProxyBase, IListIt
 
     public ITag[] Tags => JSModelMapper.ParseTags(Data);
 
-    public IDetails? Details => JSModelMapper.ParseDetails(Data, Connection);
+    public IDetails? Details => _details.Value;
 
     public string Section => JSModelMapper.GetString(Data, "section") ?? string.Empty;
 
@@ -60,20 +70,32 @@ internal sealed partial class JSListItemAdapter : JSObservableProxyBase, IListIt
         {
             if (propertyName == "command")
             {
-                Volatile.Write(ref _command, CreateCommand());
-                break;
+                _command.Reset();
+            }
+            else if (propertyName == "moreCommands")
+            {
+                _moreCommands.Reset();
+            }
+            else if (propertyName == "details")
+            {
+                _details.Reset();
             }
         }
     }
 
-    private Lazy<ICommand?> CreateCommand()
+    public override void Dispose()
     {
-        return new Lazy<ICommand?>(() =>
-        {
-            return JSModelMapper.TryGetCommandData(Data, out var commandData)
-                ? JSCommandFactory.CreateCommandFromJson(commandData, Connection)
-                : null;
-        });
+        _moreCommands.Dispose();
+        _details.Dispose();
+        _command.Dispose();
+        base.Dispose();
+    }
+
+    private ICommand? CreateCommand()
+    {
+        return JSModelMapper.TryGetCommandData(Data, out var commandData)
+            ? JSCommandFactory.CreateCommandFromJson(commandData, Connection)
+            : null;
     }
 
     private static string GetNotificationId(JsonElement data)

src/modules/cmdpal/Microsoft.CmdPal.JsonRpc/Models/JSListPageProxy.cs

@@ -35,6 +35,8 @@ internal sealed partial class JSListPageProxy : JSObservableProxyBase, IListPage
     private readonly string _pageId;
     private readonly PageRegistry _registry;
     private readonly object _stateLock = new();
+    private readonly JSLazyCache<IFilters?> _filters;
+    private readonly JSLazyCache<ICommandItem?> _emptyContent;
     private bool? _hasMoreItemsState;
     private bool _disposed;
 
@@ -42,6 +44,10 @@ internal sealed partial class JSListPageProxy : JSObservableProxyBase, IListPage
         : base(pageId, connection, pageData)
     {
         _pageId = pageId ?? throw new ArgumentNullException(nameof(pageId));
+        _filters = new JSLazyCache<IFilters?>(CreateFilters);
+        _emptyContent = new JSLazyCache<ICommandItem?>(
+            CreateEmptyContent,
+            JSLazyCache<ICommandItem?>.DisposeValue);
 
         // Get the retained registry before subscribing. ConditionalWeakTable may run
         // the factory on a thread that loses the race and discards its result. If the
@@ -77,19 +83,7 @@ internal sealed partial class JSListPageProxy : JSObservableProxyBase, IListPage
 
     public bool ShowDetails => JSModelMapper.GetBool(Data, "showDetails", false);
 
-    public IFilters? Filters
-    {
-        get
-        {
-            if (JSModelMapper.TryGetProperty(Data, "filters", out var filtersProp) &&
-                filtersProp.ValueKind == JsonValueKind.Object)
-            {
-                return new JSFiltersAdapter(filtersProp, Connection, _pageId);
-            }
-
-            return null;
-        }
-    }
+    public IFilters? Filters => _filters.Value;
 
     public IGridProperties? GridProperties => JSModelMapper.ParseGridProperties(Data);
 
@@ -107,19 +101,7 @@ internal sealed partial class JSListPageProxy : JSObservableProxyBase, IListPage
         }
     }
 
-    public ICommandItem? EmptyContent
-    {
-        get
-        {
-            if (JSModelMapper.TryGetProperty(Data, "emptyContent", out var emptyProp) &&
-                emptyProp.ValueKind == JsonValueKind.Object)
-            {
-                return new JSCommandItemAdapter(emptyProp, Connection);
-            }
-
-            return null;
-        }
-    }
+    public ICommandItem? EmptyContent => _emptyContent.Value;
 
     public IListItem[] GetItems()
     {
@@ -309,6 +291,8 @@ internal sealed partial class JSListPageProxy : JSObservableProxyBase, IListPage
 
         _disposed = true;
 
+        _filters.Dispose();
+        _emptyContent.Dispose();
         base.Dispose();
 
         if (_registry.Pages.TryGetValue(_pageId, out var list))
@@ -395,18 +379,44 @@ internal sealed partial class JSListPageProxy : JSObservableProxyBase, IListPage
 
     protected override void OnPropertyChangesApplied(IReadOnlyList<string> propertyNames)
     {
-        if (!propertyNames.Contains("hasMoreItems"))
+        foreach (var propertyName in propertyNames)
         {
-            return;
+            if (propertyName == "filters")
+            {
+                _filters.Reset();
+            }
+            else if (propertyName == "emptyContent")
+            {
+                _emptyContent.Reset();
+            }
         }
 
-        var value = JSModelMapper.GetBool(Data, "hasMoreItems", false);
-        lock (_stateLock)
+        if (propertyNames.Contains("hasMoreItems"))
         {
-            _hasMoreItemsState = value;
+            var value = JSModelMapper.GetBool(Data, "hasMoreItems", false);
+            lock (_stateLock)
+            {
+                _hasMoreItemsState = value;
+            }
         }
     }
 
+    private IFilters? CreateFilters()
+    {
+        return JSModelMapper.TryGetProperty(Data, "filters", out var filtersProp) &&
+            filtersProp.ValueKind == JsonValueKind.Object
+            ? new JSFiltersAdapter(filtersProp, Connection, _pageId)
+            : null;
+    }
+
+    private ICommandItem? CreateEmptyContent()
+    {
+        return JSModelMapper.TryGetProperty(Data, "emptyContent", out var emptyProp) &&
+            emptyProp.ValueKind == JsonValueKind.Object
+            ? new JSCommandItemAdapter(emptyProp, Connection)
+            : null;
+    }
+
     private IListItem[] ParseListItems(JsonElement? result)
     {
         if (!result.HasValue)

src/modules/cmdpal/Microsoft.CmdPal.JsonRpc/Models/JSModelMapper.cs

@@ -284,6 +284,47 @@ internal static class JSModelMapper
         return items.ToArray();
     }
 
+    internal static void DisposeContextItems(IEnumerable<IContextItem> items)
+    {
+        foreach (var item in items)
+        {
+            if (item is not ICommandContextItem commandItem)
+            {
+                continue;
+            }
+
+            DisposeContextItems(commandItem.MoreCommands);
+            if (commandItem.Command is IDisposable disposable)
+            {
+                disposable.Dispose();
+            }
+        }
+    }
+
+    internal static void DisposeDetails(IDetails? details)
+    {
+        if (details is null)
+        {
+            return;
+        }
+
+        foreach (var element in details.Metadata)
+        {
+            if (element.Data is not IDetailsCommands commands)
+            {
+                continue;
+            }
+
+            foreach (var command in commands.Commands ?? [])
+            {
+                if (command is IDisposable disposable)
+                {
+                    disposable.Dispose();
+                }
+            }
+        }
+    }
+
     internal static ICommandContextItem ParseContextItem(JsonElement element, JsonRpcConnection connection)
     {
         var command = JSCommandFactory.CreateCommandFromJson(GetCommandData(element), connection);

src/modules/cmdpal/Microsoft.CmdPal.JsonRpc/Models/JSPropertyChangeRegistry.cs

@@ -18,10 +18,26 @@ internal static class JSPropertyChangeRegistry
     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)
+        while (true)
         {
-            targets.Add(new WeakReference<IJSPropertyChangeTarget>(target));
+            var targets = registry.Targets.GetOrAdd(commandId, static _ => []);
+            lock (targets)
+            {
+                if (!registry.Targets.TryGetValue(commandId, out var currentTargets) ||
+                    !ReferenceEquals(targets, currentTargets))
+                {
+                    continue;
+                }
+
+                targets.RemoveAll(reference => !reference.TryGetTarget(out _));
+                if (!targets.Exists(reference =>
+                    reference.TryGetTarget(out var current) && ReferenceEquals(current, target)))
+                {
+                    targets.Add(new WeakReference<IJSPropertyChangeTarget>(target));
+                }
+
+                return;
+            }
         }
     }
 
@@ -39,7 +55,7 @@ internal static class JSPropertyChangeRegistry
                 !reference.TryGetTarget(out var current) || ReferenceEquals(current, target));
             if (targets.Count == 0)
             {
-                registry.Targets.TryRemove(commandId, out _);
+                RemoveTargets(registry, commandId, targets);
             }
         }
     }
@@ -73,6 +89,11 @@ internal static class JSPropertyChangeRegistry
                     liveTargets.Add(target);
                 }
             }
+
+            if (targets.Count == 0)
+            {
+                RemoveTargets(registry, commandId, targets);
+            }
         }
 
         foreach (var target in liveTargets)
@@ -81,6 +102,29 @@ internal static class JSPropertyChangeRegistry
         }
     }
 
+    internal static int GetRegistrationCount(JsonRpcConnection connection, string commandId)
+    {
+        if (!Registries.TryGetValue(connection, out var registry) ||
+            !registry.Targets.TryGetValue(commandId, out var targets))
+        {
+            return 0;
+        }
+
+        lock (targets)
+        {
+            return targets.Count;
+        }
+    }
+
+    private static void RemoveTargets(
+        Registry registry,
+        string commandId,
+        List<WeakReference<IJSPropertyChangeTarget>> targets)
+    {
+        ((ICollection<KeyValuePair<string, List<WeakReference<IJSPropertyChangeTarget>>>>)registry.Targets)
+            .Remove(new KeyValuePair<string, List<WeakReference<IJSPropertyChangeTarget>>>(commandId, targets));
+    }
+
     private sealed class Registry
     {
         internal ConcurrentDictionary<string, List<WeakReference<IJSPropertyChangeTarget>>> Targets { get; } = new();

src/modules/cmdpal/Tests/Microsoft.CmdPal.JsonRpc.UnitTests/JSAdapterLifecycleTests.cs

@@ -3,10 +3,13 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.Runtime.CompilerServices;
+using System.Text.Json;
 using System.Text.Json.Nodes;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CmdPal.JsonRpc.Models;
+using Microsoft.CommandPalette.Extensions;
 using Microsoft.CommandPalette.Extensions.Toolkit;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 
@@ -14,6 +17,204 @@ namespace Microsoft.CmdPal.JsonRpc.UnitTests;
 
 public partial class JSAdapterTests
 {
+    [TestMethod]
+    public void PropertyChangeRegistry_PrunesDeadTargetsAndDeduplicatesLiveTargets()
+    {
+        using var fake = new JSFakeExtension();
+        const string commandId = "shared-command";
+        var deadTarget = RegisterTemporaryTarget(fake.Connection, commandId);
+
+        GC.Collect();
+        GC.WaitForPendingFinalizers();
+        GC.Collect();
+
+        Assert.IsFalse(deadTarget.TryGetTarget(out _));
+        Assert.AreEqual(1, JSPropertyChangeRegistry.GetRegistrationCount(fake.Connection, commandId));
+
+        var liveTarget = new RecordingPropertyChangeTarget();
+        Parallel.For(
+            0,
+            64,
+            _ => JSPropertyChangeRegistry.Register(fake.Connection, commandId, liveTarget));
+
+        Assert.AreEqual(1, JSPropertyChangeRegistry.GetRegistrationCount(fake.Connection, commandId));
+
+        JSPropertyChangeRegistry.Dispatch(
+            fake.Connection,
+            ParseElement(new JsonObject
+            {
+                ["commandId"] = commandId,
+                ["properties"] = new JsonObject { ["title"] = "updated" },
+            }));
+
+        Assert.AreEqual(1, liveTarget.ApplyCount);
+        JSPropertyChangeRegistry.Unregister(fake.Connection, commandId, liveTarget);
+    }
+
+    [TestMethod]
+    public void NestedProxyGetters_CacheIdentityAndRegistration()
+    {
+        using var fake = new JSFakeExtension();
+        using var settings = new JSCommandSettingsProxy("settings", fake.Connection);
+        using var listPage = new JSListPageProxy(
+            "list-page",
+            fake.Connection,
+            ParseElement(new JsonObject
+            {
+                ["id"] = "list-page",
+                ["filters"] = new JsonObject { ["filters"] = new JsonArray() },
+                ["emptyContent"] = CommandItem("empty-command"),
+            }));
+        using var contentPage = new JSContentPageProxy(
+            "content-page",
+            fake.Connection,
+            ParseElement(new JsonObject
+            {
+                ["id"] = "content-page",
+                ["details"] = new JsonObject { ["title"] = "Details" },
+                ["commands"] = new JsonArray(ContextItem("content-command")),
+            }));
+        using var commandItem = new JSCommandItemAdapter(
+            ParseElement(new JsonObject
+            {
+                ["id"] = "command-item",
+                ["title"] = "Command",
+                ["moreCommands"] = new JsonArray(ContextItem("command-more")),
+            }),
+            fake.Connection);
+        using var listItem = new JSListItemAdapter(
+            ParseElement(new JsonObject
+            {
+                ["id"] = "list-item",
+                ["title"] = "List",
+                ["details"] = new JsonObject { ["title"] = "Details" },
+                ["moreCommands"] = new JsonArray(ContextItem("list-more")),
+            }),
+            fake.Connection);
+        using var fallbackItem = new JSFallbackCommandItemAdapter(
+            ParseElement(new JsonObject
+            {
+                ["id"] = "fallback-item",
+                ["title"] = "Fallback",
+                ["command"] = Command("fallback-command"),
+                ["moreCommands"] = new JsonArray(ContextItem("fallback-more")),
+            }),
+            fake.Connection);
+        var concurrentSettingsPages = new IContentPage[64];
+        Parallel.For(0, concurrentSettingsPages.Length, i => concurrentSettingsPages[i] = settings.SettingsPage);
+
+        foreach (var settingsPage in concurrentSettingsPages)
+        {
+            Assert.AreSame(settings.SettingsPage, settingsPage);
+        }
+
+        Assert.AreSame(listPage.Filters, listPage.Filters);
+        Assert.AreSame(listPage.EmptyContent, listPage.EmptyContent);
+        Assert.AreSame(contentPage.Details, contentPage.Details);
+        Assert.AreSame(contentPage.Commands, contentPage.Commands);
+        Assert.AreSame(commandItem.MoreCommands, commandItem.MoreCommands);
+        Assert.AreSame(listItem.MoreCommands, listItem.MoreCommands);
+        Assert.AreSame(listItem.Details, listItem.Details);
+        Assert.AreSame(fallbackItem.MoreCommands, fallbackItem.MoreCommands);
+
+        Assert.AreEqual(1, JSPropertyChangeRegistry.GetRegistrationCount(fake.Connection, "empty-command"));
+        Assert.AreEqual(1, JSPropertyChangeRegistry.GetRegistrationCount(fake.Connection, "content-command"));
+        Assert.AreEqual(1, JSPropertyChangeRegistry.GetRegistrationCount(fake.Connection, "command-more"));
+        Assert.AreEqual(1, JSPropertyChangeRegistry.GetRegistrationCount(fake.Connection, "list-more"));
+        Assert.AreEqual(1, JSPropertyChangeRegistry.GetRegistrationCount(fake.Connection, "fallback-more"));
+    }
+
+    [TestMethod]
+    public void NestedProxyGetters_InvalidateOnlyTheChangedProperty()
+    {
+        using var fake = new JSFakeExtension();
+        using var item = new JSListItemAdapter(
+            ParseElement(new JsonObject
+            {
+                ["id"] = "list-item",
+                ["title"] = "Before",
+                ["details"] = new JsonObject { ["title"] = "Old details" },
+                ["moreCommands"] = new JsonArray(ContextItem("old-more")),
+            }),
+            fake.Connection);
+        var originalDetails = item.Details;
+        var originalMoreCommands = item.MoreCommands;
+
+        JSPropertyChangeRegistry.Dispatch(
+            fake.Connection,
+            ParseElement(new JsonObject
+            {
+                ["commandId"] = "list-item",
+                ["properties"] = new JsonObject { ["title"] = "After" },
+            }));
+
+        Assert.AreEqual("After", item.Title);
+        Assert.AreSame(originalDetails, item.Details);
+        Assert.AreSame(originalMoreCommands, item.MoreCommands);
+
+        JSPropertyChangeRegistry.Dispatch(
+            fake.Connection,
+            ParseElement(new JsonObject
+            {
+                ["commandId"] = "list-item",
+                ["properties"] = new JsonObject
+                {
+                    ["details"] = new JsonObject { ["title"] = "New details" },
+                    ["moreCommands"] = new JsonArray(ContextItem("new-more")),
+                },
+            }));
+
+        Assert.AreEqual("New details", item.Details?.Title);
+        Assert.AreNotSame(originalDetails, item.Details);
+        Assert.AreNotSame(originalMoreCommands, item.MoreCommands);
+        Assert.AreEqual(0, JSPropertyChangeRegistry.GetRegistrationCount(fake.Connection, "old-more"));
+        Assert.AreEqual(1, JSPropertyChangeRegistry.GetRegistrationCount(fake.Connection, "new-more"));
+    }
+
+    [TestMethod]
+    public void ProviderSettings_ConcurrentReadsReturnOneProxy()
+    {
+        using var fake = new JSFakeExtension();
+        var requestCount = 0;
+        fake.OnRequest("provider/getSettings", _ =>
+        {
+            Interlocked.Increment(ref requestCount);
+            return new JsonObject { ["id"] = "settings-page" };
+        });
+        using var provider = CreateProvider(fake);
+        var settings = new ICommandSettings?[64];
+
+        Parallel.For(0, settings.Length, i => settings[i] = provider.Settings);
+
+        Assert.AreEqual(1, requestCount);
+        foreach (var current in settings)
+        {
+            Assert.AreSame(settings[0], current);
+        }
+    }
+
+    [TestMethod]
+    public async Task ProviderSettings_DisposeDuringRequestDoesNotPublishProxy()
+    {
+        using var fake = new JSFakeExtension();
+        using var requestStarted = new ManualResetEventSlim();
+        using var releaseRequest = new ManualResetEventSlim();
+        fake.OnRequest("provider/getSettings", _ =>
+        {
+            requestStarted.Set();
+            releaseRequest.Wait(Timeout);
+            return new JsonObject { ["id"] = "settings-page" };
+        });
+        using var provider = CreateProvider(fake);
+
+        var settings = Task.Run(() => provider.Settings);
+        Assert.IsTrue(requestStarted.Wait(Timeout));
+        provider.Dispose();
+        releaseRequest.Set();
+
+        Assert.IsNull(await settings.WaitAsync(Timeout));
+    }
+
     // LoadMore folds the loaded page into pagination state and raises
     // ItemsChanged so the host asks GetItems again and sees the appended items.
     // It stops once the extension reports the final page.
@@ -216,4 +417,43 @@ public partial class JSAdapterTests
         Assert.IsTrue(host.HiddenCount >= 1);
         Assert.IsTrue(host.HiddenCount <= host.ShownCount);
     }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    private static WeakReference<RecordingPropertyChangeTarget> RegisterTemporaryTarget(
+        JsonRpcConnection connection,
+        string commandId)
+    {
+        var target = new RecordingPropertyChangeTarget();
+        JSPropertyChangeRegistry.Register(connection, commandId, target);
+        return new WeakReference<RecordingPropertyChangeTarget>(target);
+    }
+
+    private static JsonObject Command(string id) => new()
+    {
+        ["id"] = id,
+        ["name"] = id,
+    };
+
+    private static JsonObject CommandItem(string id) => new()
+    {
+        ["id"] = id,
+        ["title"] = id,
+        ["command"] = Command(id),
+    };
+
+    private static JsonObject ContextItem(string id) => new()
+    {
+        ["title"] = id,
+        ["command"] = Command(id),
+    };
+
+    private sealed class RecordingPropertyChangeTarget : IJSPropertyChangeTarget
+    {
+        public int ApplyCount { get; private set; }
+
+        public void ApplyPropertyChanges(JsonElement properties)
+        {
+            ApplyCount++;
+        }
+    }
 }