fix: preload error page modules before client rendering

[svelte-triage-bot]

• Client startup and hydration await root and route error modules, but branch-only SSR preloads omit them.
• Keep eager error components for synchronous boundaries and offline fallback. Preserve SSR boundaries from feat: allow error boundaries to catch errors on the server #15308 and shared depth selection from fix: render the nearest +error.svelte at the depth it occupies when an error is thrown during rendering #16526 and chore: share the nearest error page walk between client and server #16774; retain loaded node metadata alongside the component chain.
• Collect existing JavaScript imports once per node index across branch nodes, applicable error nodes, and the root error. Reject lazy boundary initialization, which changes synchronous/offline semantics, and eager error CSS/font inclusion, which applies unused styles.
• Cover normal, load-error, 404, prerendered, and no-SSR responses. Load only metadata for no-SSR error pages, preserving browser-only components and the asset behavior from fix: link stylesheets and fonts in the head even when SSR is disabled #15718. Reuse filtered path/Link-header emission from chore: DRY out preload link/header logic #16445; keep CSR-disabled and inline outputs unchanged.

Fixes #17415

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 2f6a46f:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/2f6a46ffd159d8d0241192b85f713684c5df748c

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/17416

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: 2f6a46f

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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