fix: fall back for npx cache subprocess check (#3560)

Co-authored-by: Alexandre Teixeira <111787685+alteixeira20@users.noreply.github.com>

src/builtin_mcp.py

@@ -8,6 +8,7 @@ Each server runs as a stdio subprocess managed by McpManager.
 import logging
 import os
 import shutil
+import subprocess
 import sys
 import asyncio
 
@@ -208,6 +209,16 @@ async def _is_npx_package_cached(npx_path, package_spec, timeout_s=5):
             stdout=asyncio.subprocess.PIPE,
             stderr=asyncio.subprocess.PIPE,
         )
+    except NotImplementedError:
+        try:
+            result = subprocess.run(
+                [npx_path, "--no-install", package_spec, "--version"],
+                capture_output=True,
+                timeout=timeout_s,
+            )
+        except (subprocess.TimeoutExpired, OSError, ValueError):
+            return False
+        return result.returncode == 0 and bool(result.stdout.strip())
     except (OSError, ValueError):
         return False
     try: