fix: revert using server read for load function fetch

[eltigerchino]

closes #12868

This PR reverts a part of the change from #12113. The issue is caused by the read implementation trying to read the static asset from the server during a fetch, but it doesn't work since the static asset isn't packaged with the serverless function. I think having the distinction between fetch and read is good here.

kit/packages/kit/src/runtime/server/fetch.js

Lines 100 to 110 in dcbe422

	} else if (read_implementation) {
	const length = manifest._.server_assets[file];
	const type = manifest.mimeTypes[file.slice(file.lastIndexOf('.'))];
	return new Response(read_implementation(file), {
	headers: {
	'Content-Length': '' + length,
	'Content-Type': type
	}
	});
	}

---

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Latest commit: 9a2fe16

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[eltigerchino]

not sure why lint is failing on src/exports/vite/public.d.ts again. Formatting the file locally reveals no changes.

[aloisklink]

I've tested this 8cba744 with aloisklink/sveltekit-2.7.0-issue-reproduction@2acc884 and it seems to work with Vercel serverless functions! See https://sveltekit-2-7-0-issue-reproduction-dp5l83ne5.vercel.app/

Be aware that this will probably cause a performance regression for Cloudflare/Node to pre-#12113.

---

I've also tested an alternative fix: aloisklink@f4aace9, which is just adding:

index 7e2177d66..417b59c93 100644
--- a/packages/kit/src/runtime/server/fetch.js
+++ b/packages/kit/src/runtime/server/fetch.js
@@ -97,7 +97,7 @@ export function create_fetch({ event, options, manifest, state, get_cookie_heade
 						return new Response(state.read(file), {
 							headers: type ? { 'content-type': type } : {}
 						});
-					} else if (read_implementation) {
+					} else if (read_implementation && file in manifest._.server_assets) {
 						const length = manifest._.server_assets[file];
 						const type = manifest.mimeTypes[file.slice(file.lastIndexOf('.'))];

According to aloisklink/sveltekit-2.7.0-issue-reproduction@c3ee13c and the Vercel preview at https://sveltekit-2-7-0-issue-reproduction-itnyzmr86.vercel.app/, it also seems to work, but I don't think it would cause the same performance regression on Cloudflare. But I unfortunately don't have a Cloudflare setup to test this!

[aloisklink]

not sure why lint is failing on src/exports/vite/public.d.ts again. Formatting the file locally reveals no changes.

Btw, I ran npx prettier --write src/exports/public.d.ts and made a PR that should fix this in #12877 Edit: it looks like the actual fix would be a bit more complicated, since we have conflicting lint rules, see #12877 (comment). Either way, this file is unrelated to the PR.

better approach possible

[dummdidumm]

I think that's right - we can actually just check if file is part of the manifest