perf: skip import graph collection outside client environments

[Nic-Polumeyv]

Addresses part of #15461

vite-plugin-sveltekit-guard builds its import_map in every environment, but the map is only read in the load hook, which bails for non-client consumers before touching it. On the svelte.dev build that makes 69% of the guard's resolveId calls (3,987 of 5,778) dead work, and the guard was the top entry in dominikg's PLUGIN_TIMINGS report in #13756. This adds the same consumer bail to resolveId.

The error chains from #14155 are unaffected because the client environment collects its own edges. Measured on the svelte.dev build with 3.0.0-next.6 and vite 8.0.16 (details in #15461 (comment)), ssr-side hook time drops from ~296s cumulative to 23ms, the build succeeds, and a planted two-hop $lib/server violation still fails with the full chain. There is no new test because the behavior is meant to be unobservable and the exact chain assertions already exist in test/apps/dev-only (dev) and test/build-errors/server-only.spec.js (build), both green with this change.

History for reviewers. #15439 added hook filters everywhere except this hook, which is blocked on vitejs/vite#21956. #15543 proposed this skip plus a node_modules importer skip and was closed pending kit 3. The ssr half was not fixed by kit 3. The node_modules half is not implemented here because it is unsafe, a library can legitimately import $app/server and its violation chain has to walk node_modules edges.

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[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 1ae3a5c:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/1ae3a5c9286ca84219a1f8f6f200689f2d9a934e

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16383

Note

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

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Latest commit: 1ae3a5c

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]

this is great, thank you!