auth.js tries to import $env/dynamic/private in SvelteKit frontend

Environment

 System:
    OS: macOS 15.0
    CPU: (8) arm64 Apple M2
    Memory: 103.59 MB / 8.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.9.0 - /usr/local/bin/node
    Yarn: 1.22.21 - /usr/local/bin/yarn
    npm: 10.5.1 - /usr/local/bin/npm
    pnpm: 9.0.3 - /usr/local/bin/pnpm
    bun: 1.1.12 - ~/.bun/bin/bun
  Browsers:
    Chrome: 126.0.6478.61
    Safari: 18.0
  npmPackages:
    @auth/sveltekit: ^1.2.0 => 1.2.0 

Reproduction URL

https://github.com/ssebastianoo/SelfStats/blob/authjs-bug/src/routes/signin/%2Bpage.svelte

Describe the issue

When trying to set up a custom sign in page the authjs library for SvelteKit tries, for some reason, to import { env } from "$env/dynamic/private"; in the client, breaking the whole app

How to reproduce

Add a custom login page following the docs

Expected behavior

$env/dynamic/private shouldn't be imported on the client

Start with the linked reproduction URL and the custom sign-in page described in the issue, then trace how the client-side page imports the Auth.js SvelteKit package. Confirm that the private environment module is not included in the client bundle, and use the reproduction to verify the app loads successfully.