Fallback `error.html` does not work on pages with `ssr = false`

[secondl1ght]

Describe the bug

As described in the SvelteKit docs here https://kit.svelte.dev/docs/errors#responses certain errors are supposed to redirect to src/error.html instead of +error.svelte. I tested this by adding the following code to the script tag of my root +layout.svelte file which has a +page.ts file adjacent to it containing export const ssr = false;.

throw error(404, { message: 'test' })

I would expect an error in the root of my app to use the built-in SvelteKit error handling and either send me to error.html or error.svelte. But neither of these actions happen. Instead it renders a blank page showing nothing at all to the user (not even a default error page). And this is printed in the browser console:

[HMR][Svelte] Unrecoverable HMR error in <+layout>: next update will trigger a full reload

I tested the same page but without the ssr = false and it falls back to the error.html page which I think is what is supposed to happen.

Client side rendered pages should still be able to have error fall backs right?

I also tested throwing an error inside a component that is rendered on the root page and it also shows no error state, instead the component is just not rendered at all and there is a blank spot on the page where the component would have loaded. I think this behaviour is not expected?

Thanks

Reproduction

https://github.com/secondl1ght/sveltekit-error-demo

Logs

No response

System Info

System:
    OS: Linux 5.15 Zorin OS 16.2
    CPU: (8) x64 11th Gen Intel(R) Core(TM) i5-1135G7 @ 2.40GHz
    Memory: 7.85 GB / 31.19 GB
    Container: Yes
    Shell: 5.0.17 - /bin/bash
  Binaries:
    Node: 16.15.1 - ~/.nvm/versions/node/v16.15.1/bin/node
    Yarn: 1.22.19 - /usr/bin/yarn
    npm: 8.11.0 - ~/.nvm/versions/node/v16.15.1/bin/npm
  Browsers:
    Brave Browser: 114.1.52.130
  npmPackages:
    @sveltejs/adapter-auto: ^2.0.0 => 2.1.0 
    @sveltejs/kit: ^1.20.4 => 1.22.3 
    svelte: ^4.0.5 => 4.0.5 
    vite: ^4.4.2 => 4.4.3

Severity

serious, but I can work around it

Additional Information

No response

[thibault60000]

No response @s3812497 ?

[eltigerchino]

This is working as described by the documentation:

• With SSR enabled, the error occurs inside handle when server side rendering the page (where you have thrown the error). Hence, it responds with the src/error.html page.
• The +error.svelte page is used when a route is not found 404 or an error is thrown during load.

That being said, I'm not sure why there isn't a fallback page for client-side errors. I'm not even sure what the solution for that would look like. Maybe it's up to the developer to catch and handle errors that happen in the browser.

Related #10201