`bun run -b nuxt build` bundle a bun (npm package) inside build

Description

Run bun run -b nuxt build with Nuxt Image will bundle a 143 MB (56.8 MB gzip) build with bun inside
(compare to a normal 38.5 MB (16.6 MB gzip) build by bun run nuxt build):

>>> bun run -b nuxt build
┌  Building Nuxt for production...
│
●  Nuxt 4.2.2 (with Nitro 2.12.9, Vite 7.3.0 and Vue 3.5.26)
│
●  Nitro preset: node-server
ℹ Building client...                                                                                                                           8:12:35 PM
ℹ vite v7.3.0 building client environment for production...                                                                                    8:12:35 PM
ℹ ✓ 105 modules transformed.                                                                                                                   8:12:36 PM
ℹ ../node_modules/.cache/nuxt/.nuxt/dist/client/manifest.json                   1.09 kB │ gzip:  0.29 kB                                 
   ...
ℹ ../node_modules/.cache/nuxt/.nuxt/dist/client/_nuxt/B0oku_3T.js             147.15 kB │ gzip: 54.69 kB                                       8:12:36 PM
ℹ ✓ built in 1.69s                                                                                                                             8:12:36 PM
✔ Client built in 1705ms                                                                                                                       8:12:36 PM
ℹ Building server...                                                                                                                           8:12:36 PM
ℹ vite v7.3.0 building ssr environment for production...                                                                                       8:12:37 PM
ℹ ✓ 51 modules transformed.                                                                                                                    8:12:37 PM
ℹ ✓ built in 520ms                                                                                                                             8:12:37 PM
✔ Server built in 534ms                                                                                                                        8:12:37 PM
✔ Generated public .output/public                                                                                                        nitro 8:12:37 PM
ℹ Building Nuxt Nitro server (preset: node-server, compatibility date: 2025-07-15)                                                       nitro 8:12:37 PM
✔ Nuxt Nitro server built                                                                                                                nitro 8:12:41 PM
  ├─ .output/server/chunks/_/error-500.mjs (5.06 kB) (2.06 kB gzip)
     ...
  └─ .output/server/package.json (1.64 kB) (616 B gzip)
Σ Total size: 143 MB (56.8 MB gzip)
ℹ sharp binaries have been included in your build for linux-x64. Make sure you deploy to the same architecture.                    @nuxt/image 8:12:48 PM
✔ You can preview this build using node .output/server/index.mjs                                                                         nitro 8:12:48 PM
│                                                                                                                                               8:12:48 PM
└  ✨ Build complete!  

>>> tree -sh .output/server/node_modules/bun
[4.0K]  .output/server/node_modules/bun
├── [4.0K]  bin
│   └── [ 99M]  bun.exe
└── [1.1K]  package.json

2 directories, 2 files   

The arg -b in bun run -b means run nuxt build by bun, which is necessary for detecting environment in code (e.g. Nuxt Content detect bun to decide whether to use bun:sqlite).

Reproduce

Just run bun run -b nuxt build with the following basic setup base on nuxt minimal template:

• package.json

{
  "name": "nuxt-app",
  "type": "module",
  "private": true,
  "scripts": {
    "build": "nuxt build",
    "dev": "nuxt dev",
    "generate": "nuxt generate",
    "preview": "nuxt preview",
    "postinstall": "nuxt prepare"
  },
  "dependencies": {
    "@nuxt/image": "^2.0.0",
    "nuxt": "^4.2.2",
    "vue": "^3.5.25",
    "vue-router": "^4.6.4"
  }
}

• nuxt.config.ts

export default defineNuxtConfig({
  modules: ['@nuxt/image']
})

• nuxt info

Nuxt project info:
|                      |                                                   |
| -------------------- | ------------------------------------------------- |
| **Operating system** | `Linux 5.15.167.4-microsoft-standard-WSL2`        |
| **CPU**              | `12th Gen Intel(R) Core(TM) i7-12700H (20 cores)` |
| **Bun version**      | `1.3.5`                                           |
| **nuxt/cli version** | `3.31.3`                                          |
| **Package manager**  | `bun@1.3.5`                                       |
| **Nuxt version**     | `4.2.2`                                           |
| **Nitro version**    | `2.12.9`                                          |
| **Builder**          | `vite@7.3.0`                                      |
| **Config**           | `modules`                                         |
| **Modules**          | `@nuxt/image@2.0.0`                               |

Start with the minimal setup in package.json and nuxt.config.ts, then compare bun run -b nuxt build with bun run nuxt build. Inspect .output/server/node_modules/bun and the Nuxt Image/Nitro build path to determine why Bun is included; done means the Bun binary is no longer bundled while the Bun runtime detection still works.