fix: resolve remote modules as external during dev prebundling so packages can re-export remote functions

[Nic-Polumeyv]

Fixes #16353.

#14583 stops dependency tracing at .remote.* files by loading them as empty modules during prebundling, so their server-only imports stay out of the client bundle. An empty module also has no exports, so a package entry that re-exports from a remote file kills the dev server during dependency optimization

[MISSING_EXPORT] "lib_echo" is not exported by ".../data.remote.js"
   1 │ export { lib_echo } from './data.remote.js';

The docs say third party libraries can provide remote functions, so this should work without per-package optimizeDeps config.

Externalizing the resolved id instead keeps tracing stopped and the export surface intact, and the dev server serves the real module through the normal transform. Build mode never ran the optimizer and stays green.

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 57d3f9c:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/57d3f9c2a3a1ca0527fb2b86953ff91bb2d20fdd

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16426

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

[changeset-bot]

🦋 Changeset detected

Latest commit: 57d3f9c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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@sveltejs/kit	Patch

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[Rich-Harris]

clever!

[pevey]

clever!

Won't this prevent the bundler from resolving $app/server?

My current workaround as of 3.0.0-next.10 is:

// vite.config.js
	optimizeDeps: {
		exclude: ['sveltekit-medusa-sdk'] // don't prebundle to prevent SvelteKit from dropping the remote functions in installed packages
	},
	ssr: {
		noExternal: ['sveltekit-medusa-sdk'] // treat the package as internal to the app so that $app/server can resolve
	},

[dummdidumm]

Could explain why exactly?
Btw I think the real solution is to have a peer dependency on Svelte so that vite-plugin-svelte does add the library as a whole to exclude ; or we adjust v-p-s to also do this for packaged with SvelteKit (peer) dependencies, because this confusion comes up often

[Nic-Polumeyv]

Won't this prevent the bundler from resolving $app/server?

No. The optimizer never resolved $app/server in the first place. $app and $env are already in Kit's own optimizeDeps.exclude, and the remote file is now external as a /@fs URL, served through the dev server pipeline. On the client the remote module is replaced by fetch proxies, so $app/server never reaches the browser.

Once this ships the optimizeDeps.exclude half of the workaround can go. On the peer dependency point, sveltekit-medusa-sdk already has the svelte peer dep and svelte field, so vite-plugin-svelte should already be adding it to ssr.noExternal. It gets prebundled anyway because prebundleSvelteLibraries defaults to true in dev, which clears the library excludes.