Downloading assets at build time causes errors

[multivac61]

Describe the bug

I want to download posters in .jpg format and transform them to .webp at build time. The new .webp files should be stored under static/posters and shown using <img src="poster/foo.webp">

vite dev --host 0.0.0.0 runs fine and everything works as expected.

If I clear the static/posters folder before running vite dev.. it also works as expected.

If I clear the folder, and then run vite build, I get the following type of errors

Error: Not found: /posters/1667492_500-1674671322.webp
    at resolve (file:///Users/olafur/dev/hvaderibio/.svelte-kit/output/server/index.js:3342:18)
    at resolve (file:///Users/olafur/dev/hvaderibio/.svelte-kit/output/server/index.js:3217:34)
    at #options.hooks.handle (file:///Users/olafur/dev/hvaderibio/.svelte-kit/output/server/index.js:3387:61)
    at respond (file:///Users/olafur/dev/hvaderibio/.svelte-kit/output/server/index.js:3215:43)

I checked in the filesystem and the files are downloaded to the correct place.

If I run vite build again, the build passes...

Reproduction

Here is an example of this in play -- multivac61/hvaderibio@6c33d82

Logs

No response

System Info

System:
    OS: macOS 13.3.1
    CPU: (10) arm64 Apple M1 Pro
    Memory: 983.39 MB / 32.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.0.0 - ~/.nvm/versions/node/v20.0.0/bin/node
    Yarn: 1.22.19 - /opt/homebrew/bin/yarn
    npm: 9.6.4 - ~/.nvm/versions/node/v20.0.0/bin/npm
  Browsers:
    Chrome: 112.0.5615.121
    Firefox: 112.0
    Safari: 16.4
  npmPackages:
    @sveltejs/adapter-auto: ^2.0.0 => 2.0.0
    @sveltejs/adapter-static: ^2.0.2 => 2.0.2
    @sveltejs/kit: ^1.15.7 => 1.15.7
    svelte: ^3.58.0 => 3.58.0
    vite: ^4.2.2 => 4.2.2

### Severity

blocking all usage of SvelteKit

### Additional Information

_No response_

[multivac61]

When I modify my svelte.config.js to implement handleHttpError that doesn't handle the error. The website works fine!

import preprocess from 'svelte-preprocess'
import adapter from '@sveltejs/adapter-static'
import { vitePreprocess } from '@sveltejs/kit/vite'

const config = {
	// Consult https://kit.svelte.dev/docs/integrations#preprocessors
	// for more information about preprocessors
	preprocess: [
		vitePreprocess(),
		preprocess({
			postcss: true
		})
	],

	kit: {
		prerender: {
			handleHttpError: () => {
				return
			}
		},
		adapter: adapter()
	}
}

export default config

[multivac61]

Thank you for marking this as a discussion @benmccann. I appreciate that this may be more of a nuanced discussion, that is should you be able to download files into the static directory at build time and have them served.

How can I achieve this? Do this step before running the build command?