[luv-292] fix: keep virtualizer scrollMargin in sync with layout shifts

[NiveditJain]

Summary

• Session log viewer was rendering entries at the wrong y-offset, exposing the page --background (#031035) under the empty virtualized container — the "page goes blue while scrolling" symptom.
• Root cause: app/components/raw-log-viewer.tsx captured useWindowVirtualizer's scrollMargin once in a callback ref reading offsetTop. The ref fires on mount only, so any layout shift above the list (async searchHookActivityAction resolving and mounting <SessionHooksPanel>, Subagents-section / per-subagent collapse-expand, window resize re-flowing StatsBar / ToolStatsGrid) left the value stale. The virtualizer then mapped window scroll → list-local coords with the wrong offset and translated each item by virtualRow.start - staleScrollMargin.
• Fix: replace the callback ref with a stable useRef<HTMLDivElement> + useLayoutEffect that re-measures via getBoundingClientRect().top + window.scrollY from a ResizeObserver on document.body and a window resize listener. Functional setScrollMargin(prev => prev === top ? prev : top) short-circuits the body-resize feedback the update itself causes.

Test plan

• bun run lint clean (one pre-existing unrelated warning in tool-input-output.tsx)
• bunx tsc -p tsconfig.json --noEmit clean
• bun run test:run — 1452/1452 unit tests pass
• bun run dev, open a session that has hook activity (so SessionHooksPanel mounts async), scroll mid-list, confirm no blue gap and entries fill the viewport
• Toggle the Subagents section / individual subagents while scrolled — entries stay aligned, no jump-into-gap
• Resize window narrower so StatsBar wraps to multiple rows — list stays aligned
• #entry-<uuid> hash navigation still scrolls to the correct entry

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Fixed an issue where log items in the Session log viewer rendered at an incorrect vertical offset when layout shifts occurred above the logs. Log positioning now remains accurate during resize and layout changes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 5fd0755e-4616-4d15-9d18-f9809e944068

📥 Commits

Reviewing files that changed from the base of the PR and between 1ace54b and d79bcda.

📒 Files selected for processing (2)

• CHANGELOG.md
• app/components/raw-log-viewer.tsx

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📝 Walkthrough

Walkthrough

The Session log viewer's scroll margin calculation is refactored from a mount-only callback ref using offsetTop to a stable useRef with useLayoutEffect that dynamically computes the scroll margin via getBoundingClientRect().top + window.scrollY, resynchronized on layout changes via ResizeObserver and window resize events, fixing incorrect vertical offsets during layout shifts.

Changes

Session Log Viewer Scroll Margin Recalculation

Layer / File(s)	Summary
Hook & Observer Logic app/components/raw-log-viewer.tsx	useLayoutEffect replaces callback ref approach; continuously calculates scrollMargin from bounding rect + scroll position, observes document.body with ResizeObserver, listens to window resize, and guards against redundant updates with equality check.
Ref Wiring app/components/raw-log-viewer.tsx	List wrapper div updated to use ref={listRef} in place of previous listCallbackRef.
Documentation CHANGELOG.md	Unreleased fix entry documents the new stable ref + useLayoutEffect flow with guard pattern and resulting behavior fix for misaligned log item offsets.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 A scroll margin so fine, now dancing in time,
ResizeObserver whispers, the layout's sublime,
No more offset quirks, just bounding rects true,
Logs rest in their place—hooray, the view's new! 🏃‍♂️✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main fix: keeping the virtualizer scrollMargin synchronized with layout shifts to resolve the y-offset rendering issue.
Description check	✅ Passed	The PR description covers the issue, root cause, fix approach, and test plan. However, the test plan section shows incomplete manual verification steps (unchecked boxes for dev environment testing).
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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