Param validators 2

[Rich-Harris]

github fucked up #4334 somehow after the base branch changed, and now i can't push to it. trying this to see if it's any better

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[Rich-Harris]

somehow #4334 is up to date now. closing

[changeset-bot]

🦋 Changeset detected

Latest commit: 3555883

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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