Error page rendered for an SSR render error is missing its CSS #17406

Describe the bug

When a component throws during SSR, the nearest +error.svelte is rendered through the error boundary, but its CSS is not added to the response. In production there's no <link rel="stylesheet"> for it, and in dev it's missing from <style data-sveltekit>. The error page is unstyled until the client loads.

The same +error.svelte rendered for an error thrown in load does get its CSS.

render_response collects stylesheets only from branch nodes (runtime/server/page/render.js), while load_error_components (runtime/server/page/index.js) loads only the error nodes' components, so their stylesheets/inline_styles are never included.

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-wipbve6z?file=src%2Froutes%2F%2Bpage.svelte

1. npm run build && npm run preview
2. View source of /: no stylesheet link for the error page's CSS, so the heading is unstyled until the client loads.
3. View source of /load-error: <link href="./_app/immutable/assets/1.[hash].css" rel="stylesheet"> is present.

npm run dev shows the same: .status is missing from <style data-sveltekit> on / but present on /load-error.

Logs

System Info

System:
  OS: Linux
Binaries:
  Node: 24
  npm: 12
  pnpm: 12
npmPackages:
  @sveltejs/adapter-node: 6.0.0
  @sveltejs/kit: 3.0.0
  @sveltejs/vite-plugin-svelte: 7.3.1
  svelte: 5.57.1
  vite: 8.3.2

Severity

annoyance

Additional Information

No response