Using preloadStrategy: 'preload-mjs' causes wrong CSS link

[srueg]

Describe the bug

Using the preloadStrategy: 'preload-mjs' option causes the stylesheet <link> to be rendered with as="script".

<link rel="preload" as="script" crossorigin="anonymous" href="/_app/immutable/assets/0.r4pxjvvX.css">

This causes a flicker of unstyled content on first load.

This only seems to be a problem since SvelteKit 2.0

Reproduction

In sevelte.config.js:

output: {
    preloadStrategy: 'preload-mjs'
},

Generated index.html file:

<link rel="preload" as="script" crossorigin="anonymous" href="/_app/immutable/assets/0.r4pxjvvX.css">

Logs

No response

System Info

System:
    OS: macOS 14.2
    CPU: (8) arm64 Apple M1
    Memory: 78.63 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 21.4.0 - /opt/homebrew/bin/node
    npm: 10.2.4 - /opt/homebrew/bin/npm
    pnpm: 8.12.0 - /opt/homebrew/bin/pnpm
    bun: 1.0.17 - /opt/homebrew/bin/bun
  Browsers:
    Chrome: 119.0.6045.159
    Safari: 17.2
  npmPackages:
    @sveltejs/adapter-cloudflare: ^3.0.0 => 3.0.0
    @sveltejs/kit: ^2.0.0 => 2.0.3
    @sveltejs/vite-plugin-svelte: ^3.0.0 => 3.0.1
    svelte: ^4.0.5 => 4.2.8
    vite: ^5.0.0 => 5.0.10

Severity

serious, but I can work around it

Additional Information

Workaround: use modulepreload as browser adoption is good enough by now.

[benmccann]

We'll be removing the option in SvelteKit 3: #11190

I'd probably just avoid setting it for now