Svelte 5: `#each` block behaving differently with `pnpm dev` vs `pnpm build`

[svelte-kit-so-good]

Describe the bug

In the +layout.svelte of the repro there are 4 variants.

• Version 1 insidiously breaks on deployment (as discussed in this closed issue 10437).
• Version 2 is the now prescribed way (?) ... which is unnecessary when using writable stores
• Version 3 actually breaks on pnpm dev 🤷‍♀️
• Version 4 just works; I've moved all the logic to a component and imported it.

Note: the repro starts with Version 3. If you run pnpm build && pnpm preview the demo works (works means the modal loads properly when clicking the options in the '/iframes' route). If you run pnpm dev the demo breaks.

Reproduction

SvelteLab demo

Logs

No response

System Info

Svelte v5.0.0-next.53; but tried as far back as alpha 20.

Severity

annoyance