fix: guard POSIX-only process functions for Windows compatibility

os.setsid, os.killpg, and os.getpgid do not exist on Windows and raise
AttributeError on import or first call. This breaks the terminal tool,
code execution sandbox, process registry, and WhatsApp bridge on Windows.

Added _IS_WINDOWS platform guard in all four affected files, following
the pattern documented in CONTRIBUTING.md. On Windows, preexec_fn is
set to None and process termination falls back to proc.terminate() /
proc.kill() instead of process group signals.

Files changed:
- tools/environments/local.py (3 call sites)
- tools/process_registry.py (2 call sites)
- tools/code_execution_tool.py (3 call sites)
- gateway/platforms/whatsapp.py (3 call sites)

gateway/platforms/whatsapp.py

@@ -19,7 +19,10 @@ import asyncio
 import json
 import logging
 import os
+import platform
 import subprocess
+
+_IS_WINDOWS = platform.system() == "Windows"
 from pathlib import Path
 from typing import Dict, List, Optional, Any
 
@@ -166,7 +169,7 @@ class WhatsAppAdapter(BasePlatformAdapter):
                 ],
                 stdout=subprocess.DEVNULL,
                 stderr=subprocess.DEVNULL,
-                preexec_fn=os.setsid,
+                preexec_fn=None if _IS_WINDOWS else os.setsid,
             )
             
             # Wait for bridge to be ready via HTTP health check
@@ -211,13 +214,19 @@ class WhatsAppAdapter(BasePlatformAdapter):
                 # Kill the entire process group so child node processes die too
                 import signal
                 try:
-                    os.killpg(os.getpgid(self._bridge_process.pid), signal.SIGTERM)
+                    if _IS_WINDOWS:
+                        self._bridge_process.terminate()
+                    else:
+                        os.killpg(os.getpgid(self._bridge_process.pid), signal.SIGTERM)
                 except (ProcessLookupError, PermissionError):
                     self._bridge_process.terminate()
                 await asyncio.sleep(1)
                 if self._bridge_process.poll() is None:
                     try:
-                        os.killpg(os.getpgid(self._bridge_process.pid), signal.SIGKILL)
+                        if _IS_WINDOWS:
+                            self._bridge_process.kill()
+                        else:
+                            os.killpg(os.getpgid(self._bridge_process.pid), signal.SIGKILL)
                     except (ProcessLookupError, PermissionError):
                         self._bridge_process.kill()
             except Exception as e: