fix: v2.5.1 — plugin npm runs no longer depend on PATH (Windows update failure)

A Windows self-update failed at "bootstrap": 'npm.cmd' is not recognized.
The update chain runs with the dashboard server's environment, whose PATH
need not reach npm.cmd, and the bootstrap looked npm up through cmd.exe
(shell: true, which also printed DEP0190).

- npmCommand() in scripts/plugin-bootstrap.js runs the npm bundled with the
  running node (npm-cli.js beside process.execPath, Windows and Unix
  layouts) with no shell, and puts that node's directory first on PATH (kept
  under the env's own Path/PATH key) so npm scripts find the same node; npm
  on PATH only when that node ships none
- Used by the runtime install, the UI build (plugin-open.js) and the
  doctor's npm row (plugin-doctor.js)

scripts/plugin-bootstrap.js

@@ -383,6 +383,29 @@ function linkCli(dir = cliDir(), root = PLUGIN_ROOT, nodePath = process.execPath
 
 /* ------------------------------------------------------------- dependencies */
 
+/**
+ * npm, run by the node executing this file: `{ file, args, env, shell }` for
+ * `spawnSync`. Its bundled `npm-cli.js` is found from `process.execPath`, so
+ * nothing depends on PATH — the self-update chain runs with the dashboard
+ * server's environment, and on Windows that PATH need not hold the directory
+ * of `npm.cmd` ("'npm.cmd' is not recognized"), even though node itself runs.
+ * PATH is still prefixed with that node's directory so npm's scripts (the UI
+ * build's `tsc`/`vite` shims) find the same node. A node with no bundled npm
+ * (a distro's split nodejs/npm packages) falls back to `npm` on PATH.
+ */
+function npmCommand(args, { execPath = process.execPath, env = process.env } = {}) {
+  const dir = path.dirname(execPath);
+  const pathKey = Object.keys(env).find((k) => k.toUpperCase() === "PATH") || "PATH";
+  const childEnv = { ...env, [pathKey]: [dir, env[pathKey]].filter(Boolean).join(path.delimiter) };
+  const cli = [
+    path.join(dir, "node_modules", "npm", "bin", "npm-cli.js"), // Windows layout
+    path.join(dir, "..", "lib", "node_modules", "npm", "bin", "npm-cli.js"), // Unix layout
+  ].find((p) => fs.existsSync(p));
+  if (cli) return { file: execPath, args: [cli, ...args], env: childEnv, shell: false };
+  const win = process.platform === "win32";
+  return { file: win ? "npm.cmd" : "npm", args, env: childEnv, shell: win };
+}
+
 /**
  * Install runtime dependencies into the runtime dir. `--ignore-scripts` keeps
  * the root postinstall from pulling the whole Vite client toolchain; the
@@ -395,12 +418,13 @@ function installDeps(rt = runtimeDir(), root = PLUGIN_ROOT) {
     const src = path.join(root, f);
     if (fs.existsSync(src)) fs.copyFileSync(src, path.join(rt, f));
   }
-  const npm = process.platform === "win32" ? "npm.cmd" : "npm";
-  const res = spawnSync(
-    npm,
-    ["install", "--omit=dev", "--ignore-scripts", "--no-audit", "--no-fund"],
-    { cwd: rt, stdio: "inherit", shell: process.platform === "win32" }
-  );
+  const npm = npmCommand(["install", "--omit=dev", "--ignore-scripts", "--no-audit", "--no-fund"]);
+  const res = spawnSync(npm.file, npm.args, {
+    cwd: rt,
+    stdio: "inherit",
+    env: npm.env,
+    shell: npm.shell,
+  });
   return res.status === 0;
 }
 
@@ -878,6 +902,7 @@ module.exports = {
   stripLegacyHooks,
   hasLegacyHooks,
   linkCli,
+  npmCommand,
   installDeps,
   serverIsLive,
   liveServers,