Describe the bug

Vite strips the base URL to avoid other middlewares from having to worry about the base URL:

Unfortunately, it doesn't really save us from having to worry about the base path and creates a number of broken / unexpected behaviors. E.g. our 404 messages print Not found: /whatever instead of Not found: /basepath/whatever.

While SvelteKit could change its own middleware, that's impossible off-the-shelf middlewares that users might. Some examples that are broken with Vite:

• https://expressjs.com/en/resources/middleware/morgan.html
• http://expressjs.com/en/resources/middleware/session.html (if cookie path is set)
• https://github.com/expressjs/express-paginate

SvelteKit does not use Vite's static asset serving because of this, but I'd love just use Vite's instead of recreating our own

Reproduction

System Info

`main`

Used Package Manager

npm

Logs

No response

Validations

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