fix: prevent dev server crash when route files are deleted

[bnn1]

closes #16642

When route files are moved or deleted during development, the existing manifest can temporarily
reference a file that no longer exists. If this happens while SvelteKit is incrementally updating
page options or generated route types, an ENOENT error escapes the filesystem watcher and
terminates the dev server.

There are two reads affected by this race:

• get_page_options reads route modules while refreshing their page options.
• createProxy reads the same modules again while updating generated route types.

Commit 8af47eb06
deliberately moved the first read outside the static-analysis try block so incorrectly resolved
paths would remain visible instead of looking like unavailable static analysis. This change
preserves that behavior.

Instead of suppressing missing-file errors at either read site, sync.update now treats ENOENT as
an aborted incremental update and reports that a full manifest rebuild is required. The dev watcher
then schedules that rebuild. Persistent path-resolution and filesystem errors remain visible through
the existing full-rebuild error handling, while transient deletion and rename races no longer crash
the process.

The regression tests cover both possible missing-source reads. The type-generation case creates a
realistic pre-existing output directory and verifies that the aborted update does not write a
partial $types.d.ts file. A separate test confirms that get_page_options continues to throw for
missing files outside the incremental-update recovery path.

Tests

Focused regression tests:

Test Files  2 passed (2)
Tests       30 passed (30)

Additional validation:

• pnpm -F @sveltejs/kit test:unit — 722 passed, 110 skipped
• pnpm -F @sveltejs/kit check — passed
• Prettier check for the changed files — passed
• git diff --check — passed

---

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Tests

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[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from d0e2a7d:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/d0e2a7d5f62311d284ef789daac1c53013118824

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16643

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: d0e2a7d

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

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[Nic-Polumeyv]

Same race can still crash one step later. sync.update continues into write_types, where createProxy does a bare fs.readFileSync on the same route files. Worth catching that too and returning a null proxy, update_types already handles that case.

[bnn1]

After reviewing the commit that introduced this behavior I realized i've been too eager to fix this.

@Nic-Polumeyv I'm looking into it, thanks

[bnn1]

can someone advise if i should convert this to draft until it's reviewed to avoid running ci/cd when updating the branch with version-3 changes?

[Rich-Harris]

thank you!