infinite redirect when serving from a subfolder with adapter-static

[xucian]

Describe the bug

I have django for backend and (trying to have) svelte on the frontend.
I'm serving the static output of sveltekit via django & whitenoise (but I can also reproduce it with a simple python server, so it's not about django).

in django, I'm returning index.html for any path that doesn't exist:
urls.py

    re_path(r'^(?!static/).*$', serve, {
        'document_root': settings.STATIC_ROOT,
        'path': 'spa/index.html'
    }),

this works fine with an angular-based front-end (using ng build --base-href=/static/spa/) , but svelte is just stuck in a redirect loop no matter what I try.

I'm doing everything I've found in docs. the initial load correctly finds all the js files and the index.html, but it just shows a white page and it infinitely redirects to something -- I can't quite debug it as it's happening really fast.

svelte.config.js

// import adapterAuto from '@sveltejs/adapter-auto';
import adapterStatic from '@sveltejs/adapter-static';
import { vitePreprocess } from '@sveltejs/vite-plugin-svelte';

/** @type {import('@sveltejs/kit').Config} */
const config = {
	// Consult https://kit.svelte.dev/docs/integrations#preprocessors
	// for more information about preprocessors
	preprocess: vitePreprocess(),

	kit: {
		adapter: adapterStatic({
			fallback: 'index.html', // SPA mode // may differ from host to host

			pages: "../.frontend-dist",
		}),
		prerender: {
			entries: []
		},
		paths: {
			base: "/static/spa",
		}
	},
};

export default config;

any help is appreciated

Reproduction

I'm sure this is immediately obvious to maintainers. please just go over my message and I'm sure you'll know why it happens, it's probably a hidden config I'm missing that I'm not aware of

Logs

No response

System Info

System:
    OS: macOS 14.6.1
    CPU: (10) arm64 Apple M1 Max
    Memory: 161.69 MB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 18.16.1 - ~/.nvm/versions/node/v18.16.1/bin/node
    npm: 9.5.1 - ~/.nvm/versions/node/v18.16.1/bin/npm
  Browsers:
    Chrome: 129.0.6668.60
    Safari: 17.6

Severity

blocking all usage of SvelteKit

Additional Information

No response