fix: ensure vite build watch mode works

[teemingc]

fixes #16624

Two changes were required:

• we need to correctly handle the result of builder.build which can return a watcher instead of the build chunks. Added a normaliser to handle that. Unfortunately, the bundle has to be taken from the generateBundle hook.
• ignore generated files during a build when the watch mode is enabled. Copied the config from the dev server watch config option

Questions:

• this remains unfixed in v2. Do we need to fix it there too?
• no test added because it seems more trouble than it's worth. That said, it did regress. I think we can add a test where we monitor the logs of the ongoing build --watch process and end it if the assertions pass? with a timeout so it doesn't go on indefinitely?

[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from 849b73d:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/849b73d34eb9cb2fa0e154230be03e606b9ea6f8

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16632

[changeset-bot]

🦋 Changeset detected

Latest commit: 849b73d

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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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-16632-svelte.vercel.app/

[Nic-Polumeyv]

What if the replacement happened in generateBundle instead, mutating chunk.code before write? That would make rebuilds correct by construction and remove normalise_build entirely. As it stands the chunk threading also still crashes; the second argument is evaluated before the watcher's first build, so it's permanently undefined (repro'd with the pkg build from 49a9699 on vite 8.0.12 and 8.2.0, same "chunks is not iterable" as #16624; the ERROR path has the same issue).

[teemingc]

The real issue is that all our logic in the buildApp hook doesn't re-run when watch mode is enabled 🤦🏼 going to enquire about this in the Vite discord before continuing