Page throwing 4xx error turns into 500 when client-side-routed

[aradalvand]

Describe the bug

If you have a page that does a throw error(403) for example, and you navigate to that page via an <a> tag on the site (i.e. using the client-side router), you'll incorrectly always get a 500 error instead.

Dead-simple repro: https://github.com/aradalvand/sveltekit-error-problem

Reproduction

1. Run git clone https://github.com/aradalvand/sveltekit-error-problem
2. Run npm i && npm run dev
3. Navigate to /foo, you'll get a 403 error, as expected.
4. Now, navigate to the home page, and click on the "Go to foo" button, now you'll get a 500 error while the page actually threw a 403.

Logs

No response

System Info

System:
    OS: Linux 5.15 Ubuntu 20.04.4 LTS (Focal Fossa)
    CPU: (4) x64 Intel(R) Core(TM) i7-7500U CPU @ 2.70GHz
    Memory: 236.17 MB / 3.77 GB
    Container: Yes
    Shell: 5.8 - /usr/bin/zsh
  Binaries:
    Node: 16.15.1 - /usr/bin/node
    npm: 8.11.0 - /usr/bin/npm
  npmPackages:
    @sveltejs/adapter-auto: next => 1.0.0-next.65
    @sveltejs/kit: next => 1.0.0-next.428
    svelte: ^3.44.0 => 3.49.0
    vite: ^3.0.4 => 3.0.9

Severity

blocking an upgrade

Additional Information

No response

[Rich-Harris]

I'm fairly sure this is a duplicate of #5952, so I'm going to close it in favour of that issue