Prerendering does not work when building Docker container

Which project does this relate to?

Start

Describe the bug

When trying to build a TanStack Start project in SPA mode with Docker Vite fails to connect to the server. The build works fine outside of Docker.

3.276 [nitro] ✔ You can preview this build using bun run .output/server/index.mjs
3.277 [prerender] Prerendering pages...
3.305
3.305  ╭───────────────── [Build Info] ────────────────────╮
3.305  │                                                   │
3.305  │  - Build Directory: .output                       │
3.305  │  - Date: 1/2/2026, 5:55:52 AM                     │
3.305  │  - Nitro Version: 3.0.1-20251230-165713-6e801e22  │
3.305  │  - Nitro Preset: bun                              │
3.305  │                                                   │
3.305  ╰───────────────────────────────────────────────────╯
3.305
3.305 ℹ Spawning preview server...
3.305 ℹ bun run ./server/index.mjs
3.305
3.324 ➜ Listening on: http://localhost:46317/ (all interfaces)
3.841 [prerender] Concurrency: 10
3.842 [prerender] Crawling: /
3.855 [prerender] Prerendered 0 pages:
3.859 error: Unable to connect. Is the computer able to access the url?
3.859   path: "http://localhost:3000/",
3.859  errno: 0,
3.859   code: "ConnectionRefused"

I've also tried forcing the Nitro port to run at 3000 which ends up with the Vite prerender server failing to start instead.

Your Example Website or App

https://github.com/NormySan/tanstack-start-spa-nitro

Steps to Reproduce the Bug or Issue

1. Download repository
2. Build the docker image with docker build -t tanstack-start/nitro .

Expected behavior

I expect it to be able to connect to the server and to the pre-rendering.

Screenshots or Videos

No response

Platform

• Router / Start Version: Router 1.132.0 and Start 1.132.0
• Nitro: Nightly at latest
• Runtime: Bun
• OS: Mac OS
• Bundler: Vite
• Bundler Version: 7.1.7

Additional context

Similar to the following issue:
https://github.com/TanStack/router/issues/5967#issuecomment-3704465609

Start with the linked reproduction repository and run its docker build -t tanstack-start/nitro . command, then compare the Vite/Nitro prerender logs with the generated .output/server/index.mjs preview entry point. Done means the Docker build can start the preview server and prerender the application without the connection-refused error.