Wrong relative path in `%sveltekit.assets%` with "malformed" url

Describe the bug

Sorry I don't know how to phrase this correctly. It happened that I had a wrong url that landed on a page where I got 404 (as it should), but %sveltekit.assets% resolves to a wrong relative path and breaks.

Reproduction

Run a sveltekit app with proper +error.svelte page and have something in the app.html referencing %sveltekit.assets%, for example:

<link rel="icon" href="%sveltekit.assets%/img/favicon.png" />

Then load a 404 url in this format:

http://example.com/somethingsomething/http://awrongurl

Inspect the generated HTML page and you get this:

<link rel="icon" href="../../img/favicon.png" />

which is wrong.

Logs

System Info

System:
    OS: Linux 6.1 Debian GNU/Linux 12 (bookworm) 12 (bookworm)
    CPU: (12) x64 Intel(R) Xeon(R) Gold 5318Y CPU @ 2.10GHz
    Memory: 11.12 GB / 15.61 GB
    Container: Yes
    Shell: 5.2.15 - /bin/bash
  Binaries:
    Node: 22.16.0 - /usr/bin/node
    npm: 11.5.2 - /usr/bin/npm

Severity

annoyance

Additional Information

I've solved it by changing kit.paths.relative to false in svelte.config.js but I still wanted to report it in case someone else stumbles upon this.

Start by reproducing the malformed URL with a SvelteKit app using a +error.svelte page and app.html referencing %sveltekit.assets%, then compare the generated relative path with the expected asset path. Check how kit.paths.relative in svelte.config.js affects this behavior; done means the favicon path remains correct for the reported 404 URL without requiring that setting to be disabled.