Non-exported `prerender` remote function causes errors

[Stadly]

Describe the bug

When I have a prerender remote function that is not exported, and then a query remote function calling it, and then using the query function from a page leads to failures:

1. In my main project:

   • Server-side rendering (full page load / refresh) of the page fails with a 500 error:

     Error: Prerendered response not found

   • Client-side navigation to the same page works correctly.

2. In a minimal reproduction on StackBlitz:

   • Building/prerendering the application fails with:

     Error: Cannot call query 'getSensitiveData' while prerendering, as prerendered pages need static data. Use 'prerender' from $app/server instead
     followed by
     Error: 500 /

I encountered this while investigating workarounds for #15712 (feature request for guarded/private prerender remote functions). I was trying to avoid creating a public endpoint by not exporting the prerender remote function.

There are no error when running the dev server. Then everything seems to work well.

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-nrsoyrr2?file=src%2Froutes%2Fdata.remote.js

Create a prerender remote function that is not exported and call it from a query:

import { prerender, query } from '$app/server';

export const getSensitiveData = query(async () => {
  // TODO: Protect this query

  return sensitiveData();
});

// Note: not exported
const sensitiveData = prerender(() => {
  return 'my data';
});

Now build the app (in some cases that fails). If not, visit a page that calls getSensitiveData(). If you client-side navigate to it, it works. If you server-side navigate to it it fails.

Logs

My main project:

[500] GET /admin/system-info
Error: Prerendered response not found
    at file:///workspaces/workspace/apps/app/.svelte-kit/output/server/chunks/prerender.js:37:25
    at process.processTicksAndRejections (node:internal/process/task_queues:104:5)
    at async file:///workspaces/workspace/apps/app/.svelte-kit/output/server/chunks/prerender.js:46:42
    at async file:///workspaces/workspace/apps/app/.svelte-kit/output/server/chunks/prerender.js:30:18


Minimal reproduction on StackBlitz:

[500] GET /
Error: Cannot call query 'getSensitiveData' while prerendering, as prerendered pages need static data. Use 'prerender' from $app/server instead
    at Module.wrapper (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/.svelte-kit/output/server/chunks/query.js:213:13)
    at eval (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/.svelte-kit/output/server/entries/pages/_page.svelte.js:22:100)
    at eval (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/.svelte-kit/output/server/chunks/root.js:3161:58)
    at Renderer.child (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/.svelte-kit/output/server/chunks/root.js:2990:20)
    at Renderer.push (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/.svelte-kit/output/server/chunks/root.js:3161:12)
    at eval (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/.svelte-kit/output/server/entries/pages/_page.svelte.js:22:17)
    at Renderer.child (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/.svelte-kit/output/server/chunks/root.js:2990:20)
    at Renderer.component (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/.svelte-kit/output/server/chunks/root.js:3072:24)
    at _page (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/.svelte-kit/output/server/entries/pages/_page.svelte.js:20:14)
    at children (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/.svelte-kit/output/server/chunks/root.js:4036:26)
Error: 500 /
To suppress or handle this error, implement `handleHttpError` in https://svelte.dev/docs/kit/configuration#prerender
    at eval (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/node_modules/@sveltejs/kit/src/core/config/options.js:244:13)
    at eval (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/node_modules/@sveltejs/kit/src/core/postbuild/prerender.js:93:25)
    at save (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/node_modules/@sveltejs/kit/src/core/postbuild/prerender.js:482:4)
    at visit (file:///home/projects/sveltejs-kit-template-default-nrsoyrr2/node_modules/@sveltejs/kit/src/core/postbuild/prerender.js:301:3)

Node.js v22.22.0

System Info

My main project:
  System:
    OS: Linux 6.6 Ubuntu 24.04.4 LTS 24.04.4 LTS (Noble Numbat)
    CPU: (32) x64 AMD RYZEN AI MAX+ PRO 395 w/ Radeon 8060S
    Memory: 24.20 GB / 46.93 GB
    Container: Yes
    Shell: 5.2.21 - /bin/bash
  Binaries:
    Node: 24.14.1 - /usr/bin/node
    npm: 11.11.0 - /usr/bin/npm
    pnpm: 10.32.1 - /usr/bin/pnpm
  Browsers:
    Chrome: 147.0.7727.55
  npmPackages:
    @sveltejs/adapter-node: ^5.5.4 => 5.5.4 
    @sveltejs/kit: ^2.57.1 => 2.57.1 
    @sveltejs/vite-plugin-svelte: ^6.2.4 => 6.2.4 
    svelte: ^5.55.3 => 5.55.3 
    vite: ^7.3.2 => 7.3.2 


Minimal reproduction on StackBlitz:
  System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 22.22.0 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.8.2 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @sveltejs/adapter-auto: ^7.0.0 => 7.0.1 
    @sveltejs/kit: ^2.48.5 => 2.57.1 
    @sveltejs/vite-plugin-svelte: ^6.2.1 => 6.2.4 
    svelte: ^5.43.8 => 5.55.3 
    vite: ^7.2.2 => 7.3.2

Severity

serious, but I can work around it

Additional Information

I guess consistently failing both at build time and in the dev server is a viable way to solve this, it we don't want to support non-exported prerender functions. But I think we should consider whether this could instead be used to solve #15712 (and by extension #11700). If non-exported remote functions are allowed but don't generate endpoints, we can maybe use them to guard prerendered data?