History

Nic Polumeyv f2648b3537 fix: end a restored reaction context at the end of its synchronous segment (#18694 ) When an async expression resumes after a pickled `await`, the thunk returned by `save()` in `reactivity/async.js` calls `restore()` to re-arm `active_reaction` for the rest of the expression, then disarms it with `queue_micro_task(unset_context)`. Any microtask already queued before that one runs inside the restored context. If it writes to a source, `set()` throws `state_unsafe_mutation` in production, since the guard is not dev-only. #18453 introduced the queued disarm and noted this case in review as unavoidable. SvelteKit hits it in practice: its fetch continuations write to internal `$state` (sveltejs/kit#16914), and a user's `$derived((await q()).length)` resuming in the same tick makes that write throw and drops the update signal. The context restored by a `save` thunk now ends with the synchronous segment it was restored in. A `restored` flag is set by the thunk and consumed on entry to `save` and `track_reactivity_loss`, so every suspension ends it; once an expression contains a pickled await, the analysis pickles every later await in it too (`has_pickled_await` on `ExpressionMetadata`), so a trailing await compiles to `$.save` rather than a bare `await`. At the end of the body, `async_thunk` in `3-transform/client/utils.js` wraps the return expression in `$.unsave(...)` when the metadata has a pickled await. If the body throws instead, the context is unset by `async_derived`'s existing `finally`, as before. The queued microtask in `save` is removed. Output is unchanged for expressions that pickle nothing (`$derived(await a)` compiles byte for byte the same). Expressions with a pickled await gain one `$.unsave(` call per body, and their trailing await becomes a `$.save`, 4 to 6 bytes gzipped in the added tests. At runtime a boolean write replaces a queued microtask per resume. `bench:compare` shows no difference outside run-to-run noise. Two runtime tests reproduce the throw without any library involved, one in dev and one with the prod `await` shape, and fail on `main`. --------- Co-authored-by: Simon Holthausen <simon.holthausen@vercel.com>		2 weeks ago
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README.md	…
async-store-sub-blocker.md	fix: make template store subscriptions wait for the promise that assigns the store (#18582 )	3 weeks ago
boundary-teardown-error-routing.md	fix: route $derived teardown errors through invoke_error_boundary (#18486 )	3 weeks ago
calm-dates-track.md	fix: track SvelteDate snapshots in reactions (#18700 )	2 weeks ago
clean-head-anchors.md	fix: clean up svelte:head anchors on unmount (#18697 )	2 weeks ago
config.json	chore: switch to @changesets/changelog-github (#18570 )	3 weeks ago
cool-spoons-tap.md	fix: warn on undeclared shorthand event handlers on svelte:window/document/body (#18480 )	3 weeks ago
fix-hmr-onoutroend-double-fire.md	fix: prevent onoutroend from firing twice when compilerOptions.hmr is true (#18655 )	3 weeks ago
gentle-spaces-print.md	fix: preserve whitespace after inline elements when printing (#18685 )	3 weeks ago
great-hoops-tickle.md	fix: run `onDestroy` callbacks when a server render throws (#18585 )	3 weeks ago
hungry-plums-roll.md	fix: don't apply scoped CSS class to elements inside <svelte:head> (#18160 )	3 weeks ago
large-schools-smell.md	fix: accept `onfocusin`/`onfocusout` in `a11y_mouse_events_have_key_events` (#18689 )	2 weeks ago
legacy-reactive-map-lookups.md	perf: O(n²)→O(n) Map lookups for legacy reactive statements (#18602 )	3 weeks ago
lemon-bikes-marry.md	fix: distinct memoizer on style/class directives (#18466 )	3 weeks ago
olive-crabs-refuse.md	fix: don't turn component instances stored in $state into state proxies (#18646 )	3 weeks ago
olive-jars-repeat.md	feat: export RenderOutput, SyncRenderOutput, Csp and Sha256Source from svelte/server (#18648 )	3 weeks ago
optimize-const-tag.md	perf: optimize simple object destructuring in @const tags (#18390 )	3 weeks ago
quiet-context-segment.md	fix: end a restored reaction context at the end of its synchronous segment (#18694 )	2 weeks ago
quiet-falcons-search.md	fix: don't resurrect outroing elements when an ancestor block is paused and resumed (#18431 )	3 weeks ago
tidy-pandas-refuse.md	fix: prevent `selectedcontent` mutation from changing the selected option (#18495 )	3 weeks ago
tough-pandas-shout.md	fix: avoid NaN keyframe values in slide transition (#18430 )	3 weeks ago
witty-donuts-explain.md	docs: clarify when `$effect.pre` runs relative to DOM updates (#18534 )	3 weeks ago
young-papers-hide.md	fix: scope SSR boundary failed snippets to their boundary (#18593 )	3 weeks ago

README.md

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