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fix: freeze effects-inside-deriveds when disconnecting, unfreeze on reconnect#17682

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freeze-derived-effects
Feb 12, 2026
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fix: freeze effects-inside-deriveds when disconnecting, unfreeze on reconnect#17682
Rich-Harris merged 6 commits into
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freeze-derived-effects

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@Rich-Harris Rich-Harris commented Feb 11, 2026 •
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This supersedes #16595, and fixes the issue by 'freezing' effects inside deriveds when those deriveds are disconnected, and unfreezing them when they reconnect. This is preferable to the current asymmetric behaviour on main (in which effects are destroyed when the derived is disconnected, and never recreated) and #16595, which causes the derived itself to be re-evaluated.

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changeset-bot Bot commented Feb 11, 2026 •
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🦋 Changeset detected

Latest commit: bfa7cc4

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package
Name Type
svelte Patch

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@Rich-Harris Rich-Harris temporarily deployed to Publish pkg.pr.new (maintainers) February 11, 2026 23:08 — with GitHub Actions Inactive
@Rich-Harris Rich-Harris mentioned this pull request Feb 11, 2026
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svelte-docs-bot Bot commented Feb 11, 2026

Preview: https://svelte-dev-git-preview-svelte-17682-svelte.vercel.app/

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github-actions Bot commented Feb 11, 2026

Playground

pnpm add https://pkg.pr.new/svelte@17682

@Rich-Harris
simplify — there's no great way to know if an effect is immediately i…
bfa7cc4 
…nside a derived that doesn't probably create more work than it saves
@Rich-Harris Rich-Harris temporarily deployed to Publish pkg.pr.new (maintainers) February 12, 2026 00:37 — with GitHub Actions Inactive
@Rich-Harris Rich-Harris marked this pull request as ready for review February 12, 2026 00:37
dummdidumm
dummdidumm approved these changes Feb 12, 2026
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This works and is a good solution, but it adds more code and I'm wondering if we should instead opt for an overall "simpler" model. I believe the main reason people run into connect/disconnect is because they create global state outside of a reactive context. So what if we allow to create deriveds/effects outside of a reactive context, and if so we warn about it and just never clean it up? This likely makes the whole connect/disconnect much simpler, and we can instead rerun deriveds when they reconnect - which is much rarer in this world.

Anyway that's all food for thought and shouldn't hold up this PR, because the current behavior definitely is more broken.

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Rich-Harris commented Feb 12, 2026

Ownership (whether or not a derived was created inside an effect tree) and connection (whether or not anything currently depends on the derived) aren't the same thing though.

Anyway, I just realised we don't handle abort signals in this PR, and in the process of fixing that realised that we're currently over-running effects for some reason... investigating

@Rich-Harris Rich-Harris temporarily deployed to Publish pkg.pr.new (maintainers) February 12, 2026 14:04 — with GitHub Actions Inactive
@Rich-Harris Rich-Harris merged commit 4eee2f7 into main Feb 12, 2026
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@Rich-Harris Rich-Harris deleted the freeze-derived-effects branch February 12, 2026 14:15
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Version Packages (#17681)
c1c664d 
This PR was opened by the [Changesets
release](https://github.com/changesets/action) GitHub action. When
you're ready to do a release, you can merge this and the packages will
be published to npm automatically. If you're not ready to do a release
yet, that's fine, whenever you add more changesets to main, this PR will
be updated.


# Releases
## [email protected]

### Patch Changes

- fix: take into account `nodeName` case sensitivity on XHTML pages
([#17689](#17689))

- fix: render `multiple` and `selected` attributes as empty strings for
XHTML compliance
([#17689](#17689))

- fix: always lowercase HTML elements, for XHTML compliance
([#17664](#17664))

- fix: freeze effects-inside-deriveds when disconnecting, unfreeze on
reconnect ([#17682](#17682))

- fix: propagate `$effect` errors to `<svelte:boundary>`
([#17684](#17684))

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
@mtsgrd mtsgrd mentioned this pull request Mar 4, 2026
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