Describe the bug

As promised in sveltejs/svelte#17787 (comment) I managed to create a reproduction of the issue.

Basically, navigating between +page.svelte of a +layout.svelte can re-evaluate their $derived using the wrong params.id before actually navigating to the other +page.svelte.

In contrast to my initial assumptions, it actually requires the layout to await a long running promise AND rerun based on params changes.

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-qhdxrvzq?file=src%2Froutes%2F%2Blayout.svelte

Logs

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: 20.19.1 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.8.2 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @sveltejs/adapter-auto: ^7.0.0 => 7.0.1 
    @sveltejs/kit: ^2.53.2 => 2.53.2 
    @sveltejs/vite-plugin-svelte: ^6.2.1 => 6.2.4 
    svelte: ^5.53.5 => 5.53.5 
    vite: ^7.2.2 => 7.3.1

Severity

serious, but I can work around it

Additional Information

I don't think #14996 (comment) applies here, as I don't see how synchronously accessing params.id before an async boundary is actually entered would be an edge case of the reactivity system.

Also, forkPreloads: false does not fix this issue