proxy route rules in 2.10 dev server force append base URL

[wug-ge]

Environment

node v22.11.0
[email protected] (error happens from 2.10.0 onwards)

Reproduction

Install new nitro project with version 2.10.x, add the following to nuxt.config.ts:

baseURL: '/app',

routeRules: {
"/api/": { proxy: "http://localhost:3000/" },
},

Given it is just this few lines in a new project, I didn't make a reproduction. If you can't reproduce the issue, I'm happy to make one though.
Be aware that "localhost:3000" is another local running server not nitro itself. My nitro project is running on localhost:3002. Please replace with any http server.

Describe the bug

With v2.9.7 if you add a baseURL like : /app and a routeRule like mentioned above, a request to /api/orders would correctly query http://localhost:3000/orders.
Since 2.10.x this behavious has been changed and instead the following happens:

• /api/orders redirects to /app/api/orders
• proxy is queried with http://localhost:3000/app/api/orders (instead of http://localhost:3000/orders)

This might be intentional, but since it is a breaking change in a minor version I decided to report it here.

Additional context

I also opened the following issue in the Nuxt repo given I encountered the problem with Nuxt, but it is certainly nitro related after I tested it more: nuxt/nuxt#29915

Logs

No response

[pi0]

Minimal reproductions:

• 2.9: https://stackblitz.com/edit/unjs-nitro-starter-qf4osm?file=nitro.config.ts
• 2.10: https://stackblitz.com/edit/unjs-nitro-starter-c8raud?file=nitro.config.ts

This is a regression from #2713 which only affects dev server proxies.

I think we should solve it by redoing #2713 as a 404 fallback handler instead.