Fix/websocket queue to main thread (#443)

* feat: Implement async method to retrieve enabled tools on the main thread

* fix: cancelable main-thread tool discovery

* chore: dispose cancellation registration and dedupe usings

---------

Co-authored-by: Jordon Harrison <Jordon.Harrison@outlook.com>

Author: dsarno

MCPForUnity/Editor/Services/Transport/Transports/WebSocketTransportClient.cs

@@ -8,9 +8,11 @@
 using System.Threading.Tasks;
 using MCPForUnity.Editor.Config;
 using MCPForUnity.Editor.Helpers;
+using MCPForUnity.Editor.Services;
 using MCPForUnity.Editor.Services.Transport;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
+using UnityEditor;
 using UnityEngine;
 
 namespace MCPForUnity.Editor.Services.Transport.Transports
@@ -65,6 +67,39 @@ public WebSocketTransportClient(IToolDiscoveryService toolDiscoveryService = nul
         public string TransportName => TransportDisplayName;
         public TransportState State => _state;
 
+        private Task<List<ToolMetadata>> GetEnabledToolsOnMainThreadAsync(CancellationToken token)
+        {
+            var tcs = new TaskCompletionSource<List<ToolMetadata>>(TaskCreationOptions.RunContinuationsAsynchronously);
+
+            // Register cancellation to break the deadlock if StopAsync is called while waiting for main thread
+            var registration = token.Register(() => tcs.TrySetCanceled());
+
+            EditorApplication.delayCall += () =>
+            {
+                try
+                {
+                    if (tcs.Task.IsCompleted)
+                    {
+                        return;
+                    }
+
+                    var tools = _toolDiscoveryService?.GetEnabledTools() ?? new List<ToolMetadata>();
+                    tcs.TrySetResult(tools);
+                }
+                catch (Exception ex)
+                {
+                    tcs.TrySetException(ex);
+                }
+                finally
+                {
+                    // Ensure registration is disposed even if discovery throws
+                    registration.Dispose();
+                }
+            };
+
+            return tcs.Task;
+        }
+
         public async Task<bool> StartAsync()
         {
             // Capture identity values on the main thread before any async context switching
@@ -421,7 +456,9 @@ private async Task SendRegisterToolsAsync(CancellationToken token)
         {
             if (_toolDiscoveryService == null) return;
 
-            var tools = _toolDiscoveryService.GetEnabledTools();
+            token.ThrowIfCancellationRequested();
+            var tools = await GetEnabledToolsOnMainThreadAsync(token).ConfigureAwait(false);
+            token.ThrowIfCancellationRequested();
             McpLog.Info($"[WebSocket] Preparing to register {tools.Count} tool(s) with the bridge.");
             var toolsArray = new JArray();