fix: resolve chat scroll anchoring and task-switch scroll race condit…

[hannesrudolph]

Summary

Fixes scroll-anchoring race conditions in the chat view by consolidating scroll tracking into Virtuoso's own callbacks, eliminating stale-closure bugs, and removing direct DOM scroll manipulation from child components.

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Related GitHub Issue

Closes: #

Description

isAtBottom state → ref

isAtBottom was React state captured in closures by handleRowHeightChange and the input area's onHeightChange. Because React batches state updates asynchronously, these callbacks frequently read stale values — the scroll position had changed but the closure still held the old boolean. Converting to a ref (isAtBottomRef) ensures every read gets the current value synchronously. This also removes isAtBottom from handleRowHeightChange's dependency array, preventing unnecessary callback re-creation that cascaded into Virtuoso row re-renders.

Consolidated scroll listeners

A useEffect attached a raw scroll event listener to the scroll container DOM element to detect when the user scrolled away from the bottom and clear stickyFollowRef. This duplicated logic already present in Virtuoso's atBottomStateChange callback, creating a race between two sources of truth for the same state. The raw listener is removed. atBottomStateChange now handles all three responsibilities: updating isAtBottomRef, toggling the scroll-to-bottom button, and clearing sticky follow.

New-task scroll anchoring

Starting a new task relied solely on Virtuoso's initialTopMostItemIndex to position the view at the bottom. When message data arrived asynchronously after mount, the view could be left stranded mid-scroll. A new block in the task?.ts effect now also sets stickyFollowRef = true and issues a requestAnimationFrame → scrollTo({ top: MAX_SAFE_INTEGER }) to cover the async race.

Removed CodeBlock outer-scroll manipulation

CodeBlock was independently tracking the outer Virtuoso scroller's position via document.querySelector and a dedicated scroll listener, then manually setting scrollTop after syntax highlighting completed. This fought Virtuoso's own scroll management. All of this is removed — outer container scrolling is now fully delegated to Virtuoso's followOutput and ChatView's handleRowHeightChange.

What changed, concretely

Aspect	Before	After
isAtBottom	React state (stale in closures)	Ref (always current)
Sticky-follow disable	Separate scroll listener + Virtuoso callback (duplicate/racing)	Single atBottomStateChange callback
New task scroll anchor	initialTopMostItemIndex only	+ sticky follow + explicit scrollTo via rAF
CodeBlock outer scroll	Direct DOM query + manual scrollTop	Delegated to Virtuoso/ChatView

Test Procedure

1. Start a new task — view should anchor to bottom immediately, even if messages load asynchronously
2. During streaming, scroll up — sticky follow should disengage and the "scroll to bottom" button should appear
3. Click "scroll to bottom" — should snap to bottom and re-engage follow
4. While at bottom, let a code block with syntax highlighting stream in — outer view should stay anchored without jitter
5. Expand/collapse a code block row while at bottom — view should smooth-scroll to maintain position
6. Expand/collapse a code block row while scrolled up — view should NOT jump

[roomote]

Rooviewer   See task

All previously flagged issues have been addressed. The cancelAnimationFrame cleanup is now properly wired into the effect's teardown.

• Cancel requestAnimationFrame in the task-switch effect cleanup to avoid stale callbacks during rapid switches

Previous reviews

• bc73cf8: Review #1

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}