fix(ui): prevent snap-to-bottom and flickering during upward session scroll

[marius-kilocode]

Problem

When scrolling up in an idle Agent Manager or chat transcript, resizing virtualized elements triggers onContentResize in createAutoScroll. When the session is inactive, this callback was unconditionally invoking scrollToBottom, forcibly snapping the viewport back to the bottom and fighting upward scroll gestures. In addition, wheel gestures did not mark user activity on the scroll tracker, causing debounced scroll handlers to misclassify user scrolls, and overflow-anchor: auto on the scroll container clashed with Virtua's virtualized scroll offset compensation.

Solution

• Auto-scroll resize guard: onContentResize now checks !userActivity.isRecent() before pinning to the bottom when inactive, allowing upward scroll gestures to proceed without interruption.
• Scroll handler fallback: Replaced the immediate bottom() snap in handleScroll for unclassified scroll shifts with a debounced pause.
• Wheel activity tracking: createUserActivity now invokes mark() on all scrollable wheel inputs (both directions) to keep the recent interaction state accurate.
• Scroll anchoring: Configured overflowAnchor: "none" on the message list scroll container to avoid competing browser-native anchor adjustments during virtual list DOM recycling.
• Unit tests: Added coverage for idle upward scrolling, content resizing, and scrollbar drag interactions.

[kilo-code-bot]

Code Review Summary

Status: 1 Issue Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	0

Incremental review of f1e5ed3: the debounced stopTimer was removed from handleScroll, which now pauses follow immediately once a scroll leaves the bottom threshold. The simplification is consistent — programmatic scrolls (bottom(), Virtua offset compensation, viewport clamping) land at ~0px from bottom so they don't trip the immediate pause, and pause() already no-ops when the user has scrolled. The removed timer's cleanup was removed with it; no new timers, listeners, or subscriptions are introduced, so no memory-leak concerns. The previously reported nested-scroll regression is unchanged and still open (existing inline comment, now at line 112).

Fix these issues in Kilo Cloud

Issue Details (click to expand)

WARNING

File	Line	Issue
packages/kilo-ui/src/hooks/create-auto-scroll.tsx	112	Nested-scroll wheel-up now pauses outer auto-follow — the upstream data-scrollable guard (present in packages/ui/src/hooks/create-auto-scroll.tsx) is missing from this variant, so wheeling up inside tool-output/code blocks stops transcript auto-follow while streaming

Files Reviewed (4 files)

• .changeset/fix-session-scroll-flicker.md - no issues (user-facing changeset present)
• packages/kilo-ui/src/hooks/create-auto-scroll.tsx - 1 issue (carried, re-verified at HEAD; incremental debounce removal reviewed — no new issues)
• packages/kilo-ui/src/hooks/scroll-user-activity.ts - no new issues (unchanged since previous review; wheel handling feeds the finding above)
• packages/kilo-ui/src/hooks/create-auto-scroll.test.tsx - no issues (unchanged since previous review; tests cover idle upward scroll, resize, scrollbar drag)

Previous Review Summary (commit c514c08)

Current summary above is authoritative. Previous snapshots are kept for context only.

Previous review (commit c514c08)

Status: 1 Issue Found | Recommendation: Address before merge

Overview

Severity	Count
CRITICAL	0
WARNING	1
SUGGESTION	0

The scroll-flicker fix itself (resize guard, debounced pause, wheel activity tracking) is sound and well-tested. One behavioral regression risk remains around nested scrollable regions in the chat transcript.

Fix these issues in Kilo Cloud

Issue Details (click to expand)

WARNING

File	Line	Issue
packages/kilo-ui/src/hooks/create-auto-scroll.tsx	129	Nested-scroll wheel-up now pauses outer auto-follow — the upstream data-scrollable guard (present in packages/ui/src/hooks/create-auto-scroll.tsx) is missing from this variant, so wheeling up inside tool-output/code blocks stops transcript auto-follow while streaming

Files Reviewed (4 files)

• .changeset/fix-session-scroll-flicker.md - no issues (user-facing changeset present)
• packages/kilo-ui/src/hooks/create-auto-scroll.tsx - 1 issue
• packages/kilo-ui/src/hooks/scroll-user-activity.ts - no issues (change reviewed; feeds the finding above)
• packages/kilo-ui/src/hooks/create-auto-scroll.test.tsx - no issues (tests cover idle upward scroll, resize, scrollbar drag; no memory leaks — timers cleaned up in onCleanup)

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_{Reviewed by kimi-k3 · Input: 25.4K · Output: 5.8K · Cached: 28K}

_{Review guidance: REVIEW.md from base branch main}