Nuxt 5 nightly dev serves 500: impound blocks dev-close-sockets.mjs #1579

Environment

• Linux
• Node 24.21.0
• pnpm 12.6.0
• nuxt-nightly@5.0.0-29841792.9ceeba8c (Nitro 3.0.260903-beta, Vite 8.3.1)
• Resolved CLI: @nuxt/cli-nightly@4.0.0-20260928-072145-54eebce

Minimal reproduction

package.json:

{
  "name": "nuxt5-cli-repro",
  "private": true,
  "type": "module",
  "scripts": { "dev": "nuxt dev" },
  "dependencies": {
    "nuxt": "npm:nuxt-nightly@5.0.0-29841792.9ceeba8c"
  }
}

nuxt.config.ts:

export default defineNuxtConfig({
  compatibilityDate: '2025-07-15'
})

app/app.vue:

<template>
  <NuxtWelcome />
</template>

Run pnpm install && CI=1 pnpm run dev, then request http://localhost:3000/.

Actual result

The CLI prints Ready, but the page returns HTTP 500. The dev log reports:

Error: This module cannot be imported in server runtime.
[importing `@nuxt/cli-nightly/runtime/dev-close-sockets.mjs` from `#nitro/virtual/plugins`]

Suggestions:
  - These are build-time only packages and cannot be used at runtime.

The error comes from impound through Vite's vite:import-analysis. The generated #nitro/virtual/plugins module imports @nuxt/cli-nightly/runtime/dev-close-sockets.mjs.

I reproduced this in a fresh temporary project with no Nuxt modules or application logic. It also occurred in an app with @nuxtjs/i18n, but i18n is not required to trigger it.

Expected result

nuxt dev should serve the minimal welcome page with HTTP 200.

Possibly related: #1570 added runtime/dev-close-sockets.mjs to the CLI. Its linked issue #1531 concerns shutdown, whereas this is a startup/server runtime import failure.