Cannot use server-only files in an app with `router.type === 'hash': when prerendering +server.ts file

Describe the bug

If you set router: { type: 'hash' } } in svelte.config.js, then you cannot have any +server files, not even prerendered ones.

The use case is that I'm building a static app using adapter-static and serving a prerendered manifest.json file via src/routes/manifest.json/+server.ts, which looks roughly like this:

import { json } from '@sveltejs/kit';
import type { WebAppManifest } from 'web-app-manifest';
import type { RequestHandler } from './$types';

export const prerender = true;

const manifest: WebAppManifest = {
	theme_color: '#020817', // hsl(222, 84%, 5%)
       ...
};

export const GET: RequestHandler = async () => {
	return json(manifest);
};

This works fine with the default router but not with the hash router. I understand the difficulties of hash routing but perhaps there is some way to make an exception for adapter-static and +server.ts files, because prerendering static data as part of applications are not uncommon, especially with adapter-static.

Reproduction

Run npm run dev or try building the below branch of the project:

• https://github.com/khromov/derivault/tree/use-hash-router-with-repro

Logs

System Info

-

Severity

serious, but I can work around it

Additional Information

No response

Start by running npm run dev and building the reproduction branch linked in the issue with router: { type: 'hash' } in svelte.config.js. Inspect how src/routes/manifest.json/+server.ts is handled during prerendering with adapter-static and compare it with the default router. Done means the prerendered endpoint works with the hash router without breaking hash-based application routing.