When using Svelte 5 release candidate with SvelteKit + a base dir + trailing slashes set to "always" relative links break

[phocks]

Describe the bug

Relative links break when using "svelte": "^5.0.0-next.1", + base: '/base/path', + export const trailingSlash = "always";

eg. tries to go to /base/path/about/about etc.

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-wmkfab?file=.vscode%2Fsnippets.json

Click on links up the top

Logs

No response

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 18.20.3 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.2.3 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @sveltejs/adapter-auto: ^3.0.0 => 3.2.1 
    @sveltejs/kit: ^2.0.0 => 2.5.10 
    @sveltejs/vite-plugin-svelte: ^3.0.0 => 3.1.0 
    svelte: ^5.0.0-next.1 => 5.0.0-next.138 
    vite: ^5.0.3 => 5.2.11

Severity

serious, but I can work around it

Additional Information

No response

[eltigerchino]

For whatever reason the anchor tag hrefs are not changing unlike Svelte 4 behaviour.
Here's a breakdown of what happens with Svelte 4:

1. During SSR, the links are rendered relative e.g., ./about/.
2. During hydration / CSR, the links are switched to root relative /base/path/about/.

What's happening with Svelte 5 now:

1. During SSR, the links are rendered relative e.g., ./about/.
2. The links are not switched to root relative /base/path/about/ and also do not change when we navigate to another page, e.g., after we navigate from the home page to the about page, the header links are still ./ and ./about/