UnityMCP stability: robust auto-restart on compile/play transitions; stop on domain reload; start/stop locking; per-project sticky ports + brief release wait; Python discovery scans hashed+legacy files and probes; editor window live status refresh.

UnityMcpBridge/Editor/Data/DefaultServerConfig.cs.meta

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UnityMcpBridge/Editor/Data/McpClients.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Helpers/GameObjectSerializer.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Helpers/PortManager.cs

@@ -2,6 +2,9 @@ using System;
 using System.IO;
 using System.Net;
 using System.Net.Sockets;
+using System.Security.Cryptography;
+using System.Text;
+using System.Threading;
 using Newtonsoft.Json;
 using UnityEngine;
 
@@ -31,15 +34,28 @@ namespace UnityMcpBridge.Editor.Helpers
         /// <returns>Port number to use</returns>
         public static int GetPortWithFallback()
         {
-            // Try to load stored port first
+            // Try to load stored port first, but only if it's from the current project
-            int storedPort = LoadStoredPort();
+            var storedConfig = GetStoredPortConfig();
-            if (storedPort > 0 && IsPortAvailable(storedPort))
+            if (storedConfig != null && 
+                storedConfig.unity_port > 0 && 
+                storedConfig.project_path == Application.dataPath &&
+                IsPortAvailable(storedConfig.unity_port))
             {
-                Debug.Log($"Using stored port {storedPort}");
+                Debug.Log($"Using stored port {storedConfig.unity_port} for current project");
-                return storedPort;
+                return storedConfig.unity_port;
             }
 
-            // If no stored port or stored port is unavailable, find a new one
+            // If stored port exists but is currently busy, wait briefly for release
+            if (storedConfig != null && storedConfig.unity_port > 0)
+            {
+                if (WaitForPortRelease(storedConfig.unity_port, 1500))
+                {
+                    Debug.Log($"Stored port {storedConfig.unity_port} became available after short wait");
+                    return storedConfig.unity_port;
+                }
+            }
+
+            // If no valid stored port, find a new one and save it
             int newPort = FindAvailablePort();
             SavePort(newPort);
             return newPort;
@@ -86,7 +102,7 @@ namespace UnityMcpBridge.Editor.Helpers
         }
 
         /// <summary>
-        /// Check if a specific port is available
+        /// Check if a specific port is available for binding
         /// </summary>
         /// <param name="port">Port to check</param>
         /// <returns>True if port is available</returns>
@@ -105,6 +121,61 @@ namespace UnityMcpBridge.Editor.Helpers
             }
         }
 
+        /// <summary>
+        /// Check if a port is currently being used by Unity MCP Bridge
+        /// This helps avoid unnecessary port changes when Unity itself is using the port
+        /// </summary>
+        /// <param name="port">Port to check</param>
+        /// <returns>True if port appears to be used by Unity MCP</returns>
+        public static bool IsPortUsedByUnityMcp(int port)
+        {
+            try
+            {
+                // Try to make a quick connection to see if it's a Unity MCP server
+                using var client = new TcpClient();
+                var connectTask = client.ConnectAsync(IPAddress.Loopback, port);
+                if (connectTask.Wait(100)) // 100ms timeout
+                {
+                    // If connection succeeded, it's likely the Unity MCP server
+                    return client.Connected;
+                }
+                return false;
+            }
+            catch
+            {
+                return false;
+            }
+        }
+
+        /// <summary>
+        /// Wait for a port to become available for a limited amount of time.
+        /// Used to bridge the gap during domain reload when the old listener
+        /// hasn't released the socket yet.
+        /// </summary>
+        private static bool WaitForPortRelease(int port, int timeoutMs)
+        {
+            int waited = 0;
+            const int step = 100;
+            while (waited < timeoutMs)
+            {
+                if (IsPortAvailable(port))
+                {
+                    return true;
+                }
+
+                // If the port is in use by an MCP instance, continue waiting briefly
+                if (!IsPortUsedByUnityMcp(port))
+                {
+                    // In use by something else; don't keep waiting
+                    return false;
+                }
+
+                Thread.Sleep(step);
+                waited += step;
+            }
+            return IsPortAvailable(port);
+        }
+
         /// <summary>
         /// Save port to persistent storage
         /// </summary>
@@ -123,7 +194,7 @@ namespace UnityMcpBridge.Editor.Helpers
                 string registryDir = GetRegistryDirectory();
                 Directory.CreateDirectory(registryDir);
 
-                string registryFile = Path.Combine(registryDir, RegistryFileName);
+                string registryFile = GetRegistryFilePath();
                 string json = JsonConvert.SerializeObject(portConfig, Formatting.Indented);
                 File.WriteAllText(registryFile, json);
 
@@ -143,11 +214,17 @@ namespace UnityMcpBridge.Editor.Helpers
         {
             try
             {
-                string registryFile = Path.Combine(GetRegistryDirectory(), RegistryFileName);
+                string registryFile = GetRegistryFilePath();
                 
                 if (!File.Exists(registryFile))
                 {
-                    return 0;
+                    // Backwards compatibility: try the legacy file name
+                    string legacy = Path.Combine(GetRegistryDirectory(), RegistryFileName);
+                    if (!File.Exists(legacy))
+                    {
+                        return 0;
+                    }
+                    registryFile = legacy;
                 }
 
                 string json = File.ReadAllText(registryFile);
@@ -170,11 +247,17 @@ namespace UnityMcpBridge.Editor.Helpers
         {
             try
             {
-                string registryFile = Path.Combine(GetRegistryDirectory(), RegistryFileName);
+                string registryFile = GetRegistryFilePath();
                 
                 if (!File.Exists(registryFile))
                 {
-                    return null;
+                    // Backwards compatibility: try the legacy file
+                    string legacy = Path.Combine(GetRegistryDirectory(), RegistryFileName);
+                    if (!File.Exists(legacy))
+                    {
+                        return null;
+                    }
+                    registryFile = legacy;
                 }
 
                 string json = File.ReadAllText(registryFile);
@@ -191,5 +274,33 @@ namespace UnityMcpBridge.Editor.Helpers
         {
             return Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.UserProfile), ".unity-mcp");
         }
+
+        private static string GetRegistryFilePath()
+        {
+            string dir = GetRegistryDirectory();
+            string hash = ComputeProjectHash(Application.dataPath);
+            string fileName = $"unity-mcp-port-{hash}.json";
+            return Path.Combine(dir, fileName);
+        }
+
+        private static string ComputeProjectHash(string input)
+        {
+            try
+            {
+                using SHA1 sha1 = SHA1.Create();
+                byte[] bytes = Encoding.UTF8.GetBytes(input ?? string.Empty);
+                byte[] hashBytes = sha1.ComputeHash(bytes);
+                var sb = new StringBuilder();
+                foreach (byte b in hashBytes)
+                {
+                    sb.Append(b.ToString("x2"));
+                }
+                return sb.ToString()[..8]; // short, sufficient for filenames
+            }
+            catch
+            {
+                return "default";
+            }
+        }
     }
 }

UnityMcpBridge/Editor/Helpers/Response.cs.meta

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UnityMcpBridge/Editor/Helpers/ServerInstaller.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Helpers/Vector3Helper.cs.meta

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UnityMcpBridge/Editor/Models/Command.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Models/MCPConfigServer.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Models/MCPConfigServers.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Models/McpClient.cs.meta

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UnityMcpBridge/Editor/Models/McpConfig.cs.meta

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UnityMcpBridge/Editor/Models/McpStatus.cs.meta

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UnityMcpBridge/Editor/Models/McpTypes.cs.meta

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UnityMcpBridge/Editor/Models/ServerConfig.cs.meta

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UnityMcpBridge/Editor/Tools/CommandRegistry.cs.meta

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UnityMcpBridge/Editor/Tools/ExecuteMenuItem.cs.meta

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UnityMcpBridge/Editor/Tools/ManageAsset.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Tools/ManageEditor.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Tools/ManageGameObject.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Tools/ManageScene.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Tools/ManageScript.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/Tools/ReadConsole.cs.meta

@@ -1,2 +1,11 @@
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UnityMcpBridge/Editor/UnityMcpBridge.cs

@@ -21,6 +21,8 @@ namespace UnityMcpBridge.Editor
         private static TcpListener listener;
         private static bool isRunning = false;
         private static readonly object lockObj = new();
+        private static readonly object startStopLock = new();
+        private static bool initScheduled = false;
         private static Dictionary<
             string,
             (string commandJson, TaskCompletionSource<string> tcs)
@@ -81,75 +83,148 @@ namespace UnityMcpBridge.Editor
 
         static UnityMcpBridge()
         {
-            Start();
+            // Use delayed initialization to avoid repeated restarts during compilation
+            EditorApplication.delayCall += InitializeAfterCompilation;
             EditorApplication.quitting += Stop;
+            AssemblyReloadEvents.beforeAssemblyReload += Stop; // ensure listener releases before domain reload
+
+            // Robust re-init hooks
+            UnityEditor.Compilation.CompilationPipeline.compilationFinished += _ => ScheduleInitRetry();
+            EditorApplication.playModeStateChanged += state =>
+            {
+                if (state == PlayModeStateChange.EnteredEditMode || state == PlayModeStateChange.EnteredPlayMode)
+                {
+                    ScheduleInitRetry();
+                }
+            };
+        }
+
+        /// <summary>
+        /// Initialize the MCP bridge after Unity is fully loaded and compilation is complete.
+        /// This prevents repeated restarts during script compilation that cause port hopping.
+        /// </summary>
+        private static void InitializeAfterCompilation()
+        {
+            initScheduled = false;
+
+            // Play-mode friendly: allow starting in play mode; only defer while compiling
+            if (EditorApplication.isCompiling)
+            {
+                ScheduleInitRetry();
+                return;
+            }
+
+            if (!isRunning)
+            {
+                Start();
+                if (!isRunning)
+                {
+                    // If a race prevented start, retry later
+                    ScheduleInitRetry();
+                }
+            }
+        }
+
+        private static void ScheduleInitRetry()
+        {
+            if (initScheduled)
+            {
+                return;
+            }
+            initScheduled = true;
+            EditorApplication.delayCall += InitializeAfterCompilation;
         }
 
         public static void Start()
         {
-            Stop();
+            lock (startStopLock)
-
-            try
             {
-                ServerInstaller.EnsureServerInstalled();
+                // Don't restart if already running on a working port
-            }
+                if (isRunning && listener != null)
-            catch (Exception ex)
-            {
-                Debug.LogError($"Failed to ensure UnityMcpServer is installed: {ex.Message}");
-            }
-
-            if (isRunning)
-            {
-                return;
-            }
-
-            try
-            {
-                // Use PortManager to get available port with automatic fallback
-                currentUnityPort = PortManager.GetPortWithFallback();
-                
-                listener = new TcpListener(IPAddress.Loopback, currentUnityPort);
-                listener.Start();
-                isRunning = true;
-                isAutoConnectMode = false; // Normal startup mode
-                Debug.Log($"UnityMcpBridge started on port {currentUnityPort}.");
-                // Assuming ListenerLoop and ProcessCommands are defined elsewhere
-                Task.Run(ListenerLoop);
-                EditorApplication.update += ProcessCommands;
-            }
-            catch (SocketException ex)
-            {
-                if (ex.SocketErrorCode == SocketError.AddressAlreadyInUse)
                 {
-                    Debug.LogError(
+                    Debug.Log($"UnityMcpBridge already running on port {currentUnityPort}");
-                        $"Port {currentUnityPort} is already in use. This should not happen with dynamic port allocation."
+                    return;
-                    );
                 }
-                else
+
+                Stop();
+
+                // Removed automatic server installer; assume server exists inside the package (UPM).
+
+                try
                 {
-                    Debug.LogError($"Failed to start TCP listener: {ex.Message}");
+                    // Try to reuse the current port if it's still available, otherwise get a new one
+                    if (currentUnityPort > 0 && PortManager.IsPortAvailable(currentUnityPort))
+                    {
+                        Debug.Log($"Reusing current port {currentUnityPort}");
+                    }
+                    else
+                    {
+                        // Use PortManager to get available port with automatic fallback
+                        currentUnityPort = PortManager.GetPortWithFallback();
+                    }
+                    
+                    listener = new TcpListener(IPAddress.Loopback, currentUnityPort);
+                    listener.Start();
+                    isRunning = true;
+                    isAutoConnectMode = false; // Normal startup mode
+                    Debug.Log($"UnityMcpBridge started on port {currentUnityPort}.");
+                    // Assuming ListenerLoop and ProcessCommands are defined elsewhere
+                    Task.Run(ListenerLoop);
+                    EditorApplication.update += ProcessCommands;
+                }
+                catch (SocketException ex)
+                {
+                    if (ex.SocketErrorCode == SocketError.AddressAlreadyInUse)
+                    {
+                        Debug.LogError(
+                            $"Port {currentUnityPort} is already in use. Trying to find alternative..."
+                        );
+                        
+                        // Try once more with a fresh port discovery
+                        try
+                        {
+                            currentUnityPort = PortManager.DiscoverNewPort();
+                            listener = new TcpListener(IPAddress.Loopback, currentUnityPort);
+                            listener.Start();
+                            isRunning = true;
+                            Debug.Log($"UnityMcpBridge started on fallback port {currentUnityPort}.");
+                            Task.Run(ListenerLoop);
+                            EditorApplication.update += ProcessCommands;
+                        }
+                        catch (Exception fallbackEx)
+                        {
+                            Debug.LogError($"Failed to start on fallback port: {fallbackEx.Message}");
+                        }
+                    }
+                    else
+                    {
+                        Debug.LogError($"Failed to start TCP listener: {ex.Message}");
+                    }
                 }
             }
         }
 
         public static void Stop()
         {
-            if (!isRunning)
+            lock (startStopLock)
             {
-                return;
+                if (!isRunning)
-            }
+                {
+                    return;
+                }
 
-            try
+                try
-            {
+                {
-                listener?.Stop();
+                    listener?.Stop();
-                listener = null;
+                    listener = null;
-                isRunning = false;
+                    isRunning = false;
-                EditorApplication.update -= ProcessCommands;
+                    EditorApplication.update -= ProcessCommands;
-                Debug.Log("UnityMcpBridge stopped.");
+                    Debug.Log("UnityMcpBridge stopped.");
-            }
+                }
-            catch (Exception ex)
+                catch (Exception ex)
-            {
+                {
-                Debug.LogError($"Error stopping UnityMcpBridge: {ex.Message}");
+                    Debug.LogError($"Error stopping UnityMcpBridge: {ex.Message}");
+                }
             }
         }
 

UnityMcpBridge/Editor/UnityMcpBridge.cs.meta

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UnityMcpBridge/Editor/Windows/ManualConfigEditorWindow.cs.meta

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UnityMcpBridge/Editor/Windows/UnityMCPEditorWindow.cs.meta

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UnityMcpBridge/Editor/Windows/UnityMcpEditorWindow.cs

@@ -58,6 +58,8 @@ namespace UnityMcpBridge.Editor.Windows
         
         private void OnFocus()
         {
+            // Refresh bridge running state on focus in case initialization completed after domain reload
+            isUnityBridgeRunning = UnityMcpBridge.IsRunning;
             if (mcpClients.clients.Count > 0 && selectedClientIndex < mcpClients.clients.Count)
             {
                 McpClient selectedClient = mcpClients.clients[selectedClientIndex];
@@ -255,6 +257,9 @@ namespace UnityMcpBridge.Editor.Windows
         {
             EditorGUILayout.BeginVertical(EditorStyles.helpBox);
             
+            // Always reflect the live state each repaint to avoid stale UI after recompiles
+            isUnityBridgeRunning = UnityMcpBridge.IsRunning;
+
             GUIStyle sectionTitleStyle = new GUIStyle(EditorStyles.boldLabel)
             {
                 fontSize = 14
@@ -458,8 +463,9 @@ namespace UnityMcpBridge.Editor.Windows
             {
                 UnityMcpBridge.Start();
             }
-
+            // Reflect the actual state post-operation (avoid optimistic toggle)
-            isUnityBridgeRunning = !isUnityBridgeRunning;
+            isUnityBridgeRunning = UnityMcpBridge.IsRunning;
+            Repaint();
         }
 
         private string WriteToConfig(string pythonDir, string configPath, McpClient mcpClient = null)

UnityMcpBridge/Editor/Windows/VSCodeManualSetupWindow.cs.meta

@@ -1,2 +1,11 @@
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+guid: 377fe73d52cf0435fabead5f50a0d204
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

UnityMcpBridge/Runtime/Serialization/UnityTypeConverters.cs.meta

@@ -1,2 +1,11 @@
 fileFormatVersion: 2
-guid: e65311c160f0d41d4a1b45a3dba8dd5a
+guid: e65311c160f0d41d4a1b45a3dba8dd5a
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+  serializedVersion: 2
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+  userData: 
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+  assetBundleVariant: 

UnityMcpServer/src/port_discovery.py

@@ -1,69 +1,133 @@
 """
 Port discovery utility for Unity MCP Server.
-Reads port configuration saved by Unity Bridge.
+
+What changed and why:
+- Unity now writes a per-project port file named like
+  `~/.unity-mcp/unity-mcp-port-<hash>.json` to avoid projects overwriting
+  each other's saved port. The legacy file `unity-mcp-port.json` may still
+  exist.
+- This module now scans for both patterns, prefers the most recently
+  modified file, and verifies that the port is actually a Unity MCP listener
+  (quick socket connect + ping) before choosing it.
 """
 
 import json
 import os
 import logging
 from pathlib import Path
-from typing import Optional
+from typing import Optional, List
+import glob
+import socket
 
 logger = logging.getLogger("unity-mcp-server")
 
 class PortDiscovery:
     """Handles port discovery from Unity Bridge registry"""
-    
+    REGISTRY_FILE = "unity-mcp-port.json"  # legacy single-project file
-    REGISTRY_FILE = "unity-mcp-port.json"
+    DEFAULT_PORT = 6400
+    CONNECT_TIMEOUT = 0.3  # seconds, keep this snappy during discovery
     
     @staticmethod
     def get_registry_path() -> Path:
         """Get the path to the port registry file"""
         return Path.home() / ".unity-mcp" / PortDiscovery.REGISTRY_FILE
     
+    @staticmethod
+    def get_registry_dir() -> Path:
+        return Path.home() / ".unity-mcp"
+    
+    @staticmethod
+    def list_candidate_files() -> List[Path]:
+        """Return candidate registry files, newest first.
+        Includes hashed per-project files and the legacy file (if present).
+        """
+        base = PortDiscovery.get_registry_dir()
+        hashed = sorted(
+            (Path(p) for p in glob.glob(str(base / "unity-mcp-port-*.json"))),
+            key=lambda p: p.stat().st_mtime,
+            reverse=True,
+        )
+        legacy = PortDiscovery.get_registry_path()
+        if legacy.exists():
+            # Put legacy at the end so hashed, per-project files win
+            hashed.append(legacy)
+        return hashed
+    
+    @staticmethod
+    def _try_probe_unity_mcp(port: int) -> bool:
+        """Quickly check if a Unity MCP listener is on this port.
+        Tries a short TCP connect, sends 'ping', expects a JSON 'pong'.
+        """
+        try:
+            with socket.create_connection(("127.0.0.1", port), PortDiscovery.CONNECT_TIMEOUT) as s:
+                s.settimeout(PortDiscovery.CONNECT_TIMEOUT)
+                try:
+                    s.sendall(b"ping")
+                    data = s.recv(512)
+                    # Minimal validation: look for a success pong response
+                    if data and b'"message":"pong"' in data:
+                        return True
+                except Exception:
+                    # Even if the ping fails, a successful TCP connect is a strong signal.
+                    # Fall back to treating the port as viable if connect succeeded.
+                    return True
+        except Exception:
+            return False
+        return False
+    
     @staticmethod
     def discover_unity_port() -> int:
         """
-        Discover Unity port from registry file with fallback to default
+        Discover Unity port by scanning per-project and legacy registry files.
+        Prefer the newest file whose port responds; fall back to first parsed
+        value; finally default to 6400.
         
         Returns:
             Port number to connect to
         """
-        registry_file = PortDiscovery.get_registry_path()
+        candidates = PortDiscovery.list_candidate_files()
-        
+
-        if registry_file.exists():
+        first_seen_port: Optional[int] = None
+
+        for path in candidates:
             try:
-                with open(registry_file, 'r') as f:
+                with open(path, 'r') as f:
-                    port_config = json.load(f)
+                    cfg = json.load(f)
-                
+                unity_port = cfg.get('unity_port')
-                unity_port = port_config.get('unity_port')
+                if isinstance(unity_port, int):
-                if unity_port and isinstance(unity_port, int):
+                    if first_seen_port is None:
-                    logger.info(f"Discovered Unity port from registry: {unity_port}")
+                        first_seen_port = unity_port
-                    return unity_port
+                    if PortDiscovery._try_probe_unity_mcp(unity_port):
-                    
+                        logger.info(f"Using Unity port from {path.name}: {unity_port}")
+                        return unity_port
             except Exception as e:
-                logger.warning(f"Could not read port registry: {e}")
+                logger.warning(f"Could not read port registry {path}: {e}")
-        
+
+        if first_seen_port is not None:
+            logger.info(f"No responsive port found; using first seen value {first_seen_port}")
+            return first_seen_port
+
         # Fallback to default port
-        logger.info("No port registry found, using default port 6400")
+        logger.info(f"No port registry found; using default port {PortDiscovery.DEFAULT_PORT}")
-        return 6400
+        return PortDiscovery.DEFAULT_PORT
     
     @staticmethod
     def get_port_config() -> Optional[dict]:
         """
-        Get the full port configuration from registry
+        Get the most relevant port configuration from registry.
+        Returns the most recent hashed file's config if present,
+        otherwise the legacy file's config. Returns None if nothing exists.
         
         Returns:
             Port configuration dict or None if not found
         """
-        registry_file = PortDiscovery.get_registry_path()
+        candidates = PortDiscovery.list_candidate_files()
-        
+        if not candidates:
-        if not registry_file.exists():
             return None
-            
+        for path in candidates:
-        try:
+            try:
-            with open(registry_file, 'r') as f:
+                with open(path, 'r') as f:
-                return json.load(f)
+                    return json.load(f)
-        except Exception as e:
+            except Exception as e:
-            logger.warning(f"Could not read port configuration: {e}")
+                logger.warning(f"Could not read port configuration {path}: {e}")
-            return None
+        return None