fix(server): use shutil.which to resolve npm for Windows compatibility

server.py

@@ -2,6 +2,7 @@
 import asyncio
 import logging
 import os
+import shutil
 import signal
 from rich.console import Console
 from rich.logging import RichHandler
@@ -42,6 +43,22 @@
 MAGMA_PATH = "./plugins/magma"
 
 
+def _resolve_npm():
+    """Resolve the full path to the npm executable.
+
+    On Windows, ``npm`` is a batch script (``npm.cmd``) that
+    ``subprocess`` cannot find without ``shell=True``.  Using
+    ``shutil.which`` resolves the correct path on every platform.
+    """
+    npm = shutil.which("npm")
+    if npm is None:
+        raise FileNotFoundError(
+            "npm is not installed or not on PATH. "
+            "Install Node.js (https://nodejs.org/) and ensure npm is available."
+        )
+    return npm
+
+
 def setup_logger(level=logging.DEBUG):
     format = "%(message)s"
     datefmt = "%Y-%m-%d %H:%M:%S"
@@ -187,9 +204,18 @@ async def enable_cors(request, response):
 
 
 async def start_vue_dev_server():
-    proc = await asyncio.create_subprocess_exec(
-        "npm", "run", "dev", stdout=sys.stdout, stderr=sys.stderr, cwd=MAGMA_PATH
-    )
+    npm = _resolve_npm()
+    if sys.platform == "win32":
+        # On Windows shutil.which resolves to npm.cmd; batch files cannot
+        # be executed directly by create_subprocess_exec, so use shell.
+        cmd = subprocess.list2cmdline([npm, "run", "dev"])
+        proc = await asyncio.create_subprocess_shell(
+            cmd, stdout=sys.stdout, stderr=sys.stderr, cwd=MAGMA_PATH,
+        )
+    else:
+        proc = await asyncio.create_subprocess_exec(
+            npm, "run", "dev", stdout=sys.stdout, stderr=sys.stderr, cwd=MAGMA_PATH,
+        )
     logging.info("VueJS development server started (PID %s).", proc.pid)
 
 
@@ -314,7 +340,9 @@ def _get_size_mb(config_key, default):
     if args.uiDevHost:
         if not os.path.exists(f"{MAGMA_PATH}/dist") and (os.path.exists(f"{MAGMA_PATH}") and len(os.listdir(MAGMA_PATH)) > 0):
             logging.info("Building VueJS front-end.")
-            subprocess.run(["npm", "run", "build"], cwd=MAGMA_PATH, check=True)
+            npm = _resolve_npm()
+            subprocess.run([npm, "run", "build"], cwd=MAGMA_PATH, check=True,
+                           shell=(sys.platform == "win32"))
             logging.info("VueJS front-end build complete.")
         else:
             logging.warning(
@@ -328,8 +356,11 @@ def _get_size_mb(config_key, default):
     if args.build:
         if os.path.exists(f"{MAGMA_PATH}") and len(os.listdir(MAGMA_PATH)) > 0:
             logging.info("Building VueJS front-end.")
-            subprocess.run(["npm", "install"], cwd=MAGMA_PATH, check=True)
-            subprocess.run(["npm", "run", "build"], cwd=MAGMA_PATH, check=True)
+            npm = _resolve_npm()
+            subprocess.run([npm, "install"], cwd=MAGMA_PATH, check=True,
+                           shell=(sys.platform == "win32"))
+            subprocess.run([npm, "run", "build"], cwd=MAGMA_PATH, check=True,
+                           shell=(sys.platform == "win32"))
             logging.info("VueJS front-end build complete.")
         else:
             logging.warning(