`resolve` return value doesn’t match type / `ResolvedPathname` type is misleading

Describe the bug

Since base was deprecated, I’ve updated my project to use the resolve function. However, I noticed that during render, resolve sometimes returns a relative path (e.g. "./about") instead of an absolute path (e.g. "/about").

The issue is that the return type, ResolvedPathname, specifies that all paths should be absolute. This makes the type misleading, since the actual return value can be relative.

I would expect one of two fixes:

1. resolve should always return absolute paths, or
2. If returning relative paths is intended, then the ResolvedPathname type should be updated so users know the real shape of the returned string.

Right now, the type and the runtime behavior don’t match.

Reproduction

https://stackblitz.com/edit/sveltejs-kit-resolve-type

Logs

Server console output:


false [ './', './about' ]


Client console output:


false ['/', './about']
true  ['/', '/about']
true  ['/', '/about']

System Info

System:
    OS: macOS 15.6.1
    CPU: (10) arm64 Apple M2 Pro
    Memory: 218.63 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.6.0 - /opt/homebrew/bin/node
    Yarn: 4.9.3 - /opt/homebrew/bin/yarn
    npm: 11.5.1 - /opt/homebrew/bin/npm
  Browsers:
    Chrome: 139.0.7258.128
    Safari: 18.6
  npmPackages:
    @sveltejs/adapter-node: ^5.3.1 => 5.3.1
    @sveltejs/kit: ^2.36.1 => 2.36.1
    @sveltejs/vite-plugin-svelte: ^6.1.3 => 6.1.3
    svelte: ^5.38.2 => 5.38.2
    vite: ^7.1.3 => 7.1.3

Severity

serious, but I can work around it

Additional Information

No response

Start with the linked StackBlitz reproduction and the resolve entry point; compare its relative-path returns with the ResolvedPathname type. Determine whether the intended result is absolute paths or an updated type, then verify that the chosen behavior matches the server and client outputs shown in the report.