fix: prevent await_reactivity_loss in notify_version

[GauBen]

closes #16914

The fix was trivial, the test was painful to write and requied ai assistance

• runs in its own file to set DEV to true globally
• has a hand-written svelte component to reproduce the issue

The diff is big because I bumped svelte to latest

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[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from ff38365:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/ff383655a9535fe8c0054d5556ad5a3ca9d77de3

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16915

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: ff38365

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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[Nic-Polumeyv]

Awesome! It might be worth doing a bigger change in the future, since this is an issue in a few places that would need to be wrapped in untrack. I'm in favor of not using runes for internal bookkeeping, as that's really the root of the problem. We could also have the svelte compiler disarm at the expression boundary instead of queueing? I haven't looked into this enough, but we can circle back. Better to get @Rich-Harris opinion, not really my lane.

I am going to dismiss my review this in favor of sveltejs/svelte#18694.

[Nic-Polumeyv]

Closing in favour of fixing this in svelte. sveltejs/svelte#18694 removes the prod throw and sveltejs/svelte#18702 removes the warning. once both are released. kit raises its svelte floor and no untrack is needed here. Thanks for the report and the repro, it's what led to fixing this!

[Nic-Polumeyv]

Reopening, untrack is the right fix. The read after await fetch in remote_request warns as designed. sveltejs/svelte#18694 still covers the prod throw.

[Nic-Polumeyv]

Awesome!

[Rich-Harris]

thank you!