Add native Windows compatibility layer

src/builtin_mcp.py

@@ -11,15 +11,36 @@ import shutil
 import sys
 import asyncio
 
+from core.platform_compat import IS_WINDOWS, which_tool
+
 logger = logging.getLogger(__name__)
 
 
 def _find_npx() -> str:
-    """Find npx binary, checking common locations if not on PATH."""
-    npx = shutil.which("npx")
+    """Find the npx binary, checking common locations if not on PATH.
+
+    On Windows the shim is `npx.cmd`, which `which_tool` resolves via PATHEXT.
+    """
+    npx = which_tool("npx")
     if npx:
         return npx
-    # Common locations when PATH is minimal (e.g. systemd)
+    if IS_WINDOWS:
+        # Minimal-PATH fallbacks: npm's global bin lives under %APPDATA%\npm,
+        # and node's installer dir carries npx.cmd alongside node.exe.
+        appdata = os.environ.get("APPDATA", os.path.expanduser("~"))
+        for candidate in (
+            os.path.join(appdata, "npm", "npx.cmd"),
+            r"C:\Program Files\nodejs\npx.cmd",
+        ):
+            if os.path.isfile(candidate):
+                return candidate
+        node = which_tool("node")
+        if node:
+            cand = os.path.join(os.path.dirname(node), "npx.cmd")
+            if os.path.isfile(cand):
+                return cand
+        return "npx.cmd"  # fallback, will fail with a clear error
+    # Common POSIX locations when PATH is minimal (e.g. systemd)
     for candidate in [
         os.path.expanduser("~/.npm-global/bin/npx"),
         os.path.expanduser("~/.local/bin/npx"),