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)

tools/code_execution_tool.py

@@ -20,6 +20,7 @@ Platform: Linux / macOS only (Unix domain sockets). Disabled on Windows.
 import json
 import logging
 import os
+import platform
 import signal
 import socket
 import subprocess
@@ -28,6 +29,8 @@ import tempfile
 import threading
 import time
 import uuid
+
+_IS_WINDOWS = platform.system() == "Windows"
 from typing import Any, Dict, List, Optional
 
 # Availability gate: UDS requires a POSIX OS
@@ -405,7 +408,7 @@ def execute_code(
             stdout=subprocess.PIPE,
             stderr=subprocess.PIPE,
             stdin=subprocess.DEVNULL,
-            preexec_fn=os.setsid,
+            preexec_fn=None if _IS_WINDOWS else os.setsid,
         )
 
         # --- Poll loop: watch for exit, timeout, and interrupt ---
@@ -514,7 +517,10 @@ def execute_code(
 def _kill_process_group(proc, escalate: bool = False):
     """Kill the child and its entire process group."""
     try:
-        os.killpg(os.getpgid(proc.pid), signal.SIGTERM)
+        if _IS_WINDOWS:
+            proc.terminate()
+        else:
+            os.killpg(os.getpgid(proc.pid), signal.SIGTERM)
     except (ProcessLookupError, PermissionError):
         try:
             proc.kill()
@@ -527,7 +533,10 @@ def _kill_process_group(proc, escalate: bool = False):
             proc.wait(timeout=5)
         except subprocess.TimeoutExpired:
             try:
-                os.killpg(os.getpgid(proc.pid), signal.SIGKILL)
+                if _IS_WINDOWS:
+                    proc.kill()
+                else:
+                    os.killpg(os.getpgid(proc.pid), signal.SIGKILL)
             except (ProcessLookupError, PermissionError):
                 try:
                     proc.kill()