fix: defer effects in pending boundary

[Rich-Harris]

just a failing test for now. #16738 (comment)

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Playground

pnpm add https://pkg.pr.new/svelte@16743

[dummdidumm]

#16971 is merged and contains one of the tests in here but no the other one - not sure what you wanna do with it

[Rich-Harris]

gonna keep it around for now, until we can come up with a fix. it's not urgent though IMHO — it handles something that's a bit of an edge case that most people will never notice

[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-svelte-16743-svelte.vercel.app/