fix: critical timezone and import bugs from code review

- Remove incorrect port safety check that treated reclaimed ports as errors
  (GetPortWithFallback may legitimately return same port if it became available)
- Fix timezone-aware vs naive datetime mixing in unity_connection.py sorting
  (use timestamp() for comparison to avoid TypeError)
- Normalize all datetime comparisons in port_discovery.py to UTC
  (file_mtime and last_heartbeat now consistently timezone-aware)
- Add missing send_with_unity_instance import in Server/tools/manage_script.py
  (was causing NameError at runtime on lines 108 and 488)

All 88 tests pass (76 passed + 5 skipped + 7 xpassed)

Author: dsarno

MCPForUnity/Editor/MCPForUnityBridge.cs

@@ -366,16 +366,18 @@ public static void Start()
                             int oldPort = currentUnityPort;
                             currentUnityPort = PortManager.GetPortWithFallback();
 
-                            // Safety check: ensure we got a different port
-                            if (currentUnityPort == oldPort)
-                            {
-                                McpLog.Error($"Port {oldPort} is occupied and no alternative port available");
-                                throw;
-                            }
-
+                            // GetPortWithFallback() may return the same port if it became available during wait
+                            // or a different port if switching to an alternative
                             if (IsDebugEnabled())
                             {
-                                McpLog.Info($"Port {oldPort} occupied, switching to port {currentUnityPort}");
+                                if (currentUnityPort == oldPort)
+                                {
+                                    McpLog.Info($"Port {oldPort} became available, proceeding");
+                                }
+                                else
+                                {
+                                    McpLog.Info($"Port {oldPort} occupied, switching to port {currentUnityPort}");
+                                }
                             }
 
                             listener = new TcpListener(IPAddress.Loopback, currentUnityPort);

MCPForUnity/UnityMcpServer~/src/unity_connection.py

@@ -484,9 +484,12 @@ def _resolve_instance_id(self, instance_identifier: Optional[str], instances: Li
                 logger.debug(f"Using default instance: {instance_identifier}")
             else:
                 # Use the most recently active instance
-                # Instances with no heartbeat (None) should be sorted last (use epoch as sentinel)
-                from datetime import datetime
-                sorted_instances = sorted(instances, key=lambda i: i.last_heartbeat or datetime.fromtimestamp(0), reverse=True)
+                # Instances with no heartbeat (None) should be sorted last (use 0 as sentinel)
+                sorted_instances = sorted(
+                    instances,
+                    key=lambda inst: inst.last_heartbeat.timestamp() if inst.last_heartbeat else 0.0,
+                    reverse=True,
+                )
                 logger.info(f"No instance specified, using most recent: {sorted_instances[0].id}")
                 return sorted_instances[0]
 

Server/port_discovery.py

@@ -16,7 +16,7 @@
 import logging
 import os
 import struct
-from datetime import datetime
+from datetime import datetime, timezone
 from pathlib import Path
 import socket
 from typing import Optional, List, Dict
@@ -238,7 +238,7 @@ def discover_all_unity_instances() -> List[UnityInstanceInfo]:
         for status_file_path in status_files:
             try:
                 status_path = Path(status_file_path)
-                file_mtime = datetime.fromtimestamp(status_path.stat().st_mtime)
+                file_mtime = datetime.fromtimestamp(status_path.stat().st_mtime, tz=timezone.utc)
 
                 with status_path.open('r') as f:
                     data = json.load(f)
@@ -258,7 +258,12 @@ def discover_all_unity_instances() -> List[UnityInstanceInfo]:
                 heartbeat_str = data.get('last_heartbeat')
                 if heartbeat_str:
                     try:
-                        last_heartbeat = datetime.fromisoformat(heartbeat_str.replace('Z', '+00:00'))
+                        parsed = datetime.fromisoformat(heartbeat_str.replace('Z', '+00:00'))
+                        # Normalize to UTC for consistent comparison
+                        if parsed.tzinfo is None:
+                            last_heartbeat = parsed.replace(tzinfo=timezone.utc)
+                        else:
+                            last_heartbeat = parsed.astimezone(timezone.utc)
                     except Exception:
                         pass
 

Server/tools/manage_script.py

@@ -6,7 +6,7 @@
 from fastmcp import FastMCP, Context
 
 from registry import mcp_for_unity_tool
-from tools import get_unity_instance_from_context
+from tools import get_unity_instance_from_context, send_with_unity_instance
 import unity_connection
 
 

Server/unity_connection.py

@@ -484,9 +484,12 @@ def _resolve_instance_id(self, instance_identifier: Optional[str], instances: Li
                 logger.debug(f"Using default instance: {instance_identifier}")
             else:
                 # Use the most recently active instance
-                # Instances with no heartbeat (None) should be sorted last (use epoch as sentinel)
-                from datetime import datetime
-                sorted_instances = sorted(instances, key=lambda i: i.last_heartbeat or datetime.fromtimestamp(0), reverse=True)
+                # Instances with no heartbeat (None) should be sorted last (use 0 as sentinel)
+                sorted_instances = sorted(
+                    instances,
+                    key=lambda inst: inst.last_heartbeat.timestamp() if inst.last_heartbeat else 0.0,
+                    reverse=True,
+                )
                 logger.info(f"No instance specified, using most recent: {sorted_instances[0].id}")
                 return sorted_instances[0]