chore: add internal development comments

[teemingc]

splitting out from #15574

---

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
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• Ideally, include a test that fails without this PR but passes with it.

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[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 6330f5c:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/6330f5cbb699d3ddaad018d4c44f0cbeef781938

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16291

[changeset-bot]

⚠️ No Changeset found

Latest commit: 6330f5c

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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Click here to learn what changesets are, and how to add one.

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16291-svelte.vercel.app/