fix(web): keep chat from jumping when the scroll-to-end pill mounts

[Yash-Singh1]

What Changed

Chat no longer remeasures the composer overlay when the scroll-to-end pill mounts. Overlay height stays whatever the composer last published; the pill only refreshes its clearance from that height.

Usage scans no longer keep aggregating cached records after a transcript file is gone. pruneScanCache now drops in-window entries under roots the walk actually completed, and leaves entries outside that window (and under unwalked roots) in place. The extra source-volume identity cache and Codex same-timestamp occurrence keys went with the old “keep usage after cleanup” path.

Why

The pill mounts and unmounts in the same commits that expand or rest the composer. A fast fling can land there while the overlay is still pinned at the previous tween height. Measuring then published that stale height against the new resting flag, dropped the timeline inset, and yanked scroll. The pill only needs clearance, so it should not drive overlay height.

Absence from a walk only proves a file is gone inside the requested window. Treating missing transcripts as still live inflated totals and needed extra identity/dedupe machinery. Evicting everything the walk did not see would also wipe 30-day cache entries whenever someone opened 7 days.

UI Changes

Fast-fling to the bottom should keep the thread still when the scroll-to-end pill appears while the composer is settling. This is a motion/layout bug; a short recording of that fling is the right evidence. None is attached here.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Cursor Grok 4.6

Summary by CodeRabbit

• Bug Fixes
  • Improved scroll-to-end behavior when the composer expands or collapses quickly.
  • Prevented stale overlay measurements from affecting the scroll-to-bottom experience.

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.5 KiB	+7 B (+0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	−2 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.5 KiB	+9 B (+0.1%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.2 KiB	56.3 KiB	+44 B (+0.1%)	66.4 KiB	✅
Codex	Live turn messages	9	10	+1 (+11.1%)	21	✅
Claude	Total thread wire	13.5 KiB	13.5 KiB	−6 B (−0.0%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	−1 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.4 KiB	6.4 KiB	−5 B (−0.1%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: 675869d · PR result: fc36861 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 113.9 KiB
• Claude decoded thread snapshot: 114.6 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[macroscopeapp]

Approvability

Verdict: Approved at fc36861

Macroscope's review found this PR approvable — This is a focused one-file fix that separates composer height measurement from scroll-to-end pill clearance, preventing pill mount/unmounts from disturbing the chat timeline. Its runtime impact is limited to localized scroll and overlay positioning behavior.

^{You can add or adjust custom eligibility rules. Learn more.}

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Advanced

Run ID: e82601c7-6ed8-4fab-a50a-fab8beb41074

📥 Commits

Reviewing files that changed from the base of the PR and between 675869d and fc36861.

📒 Files selected for processing (1)

• apps/web/src/components/ChatView.tsx

Included review availability: Your plan provides up to 10 included reviews per hour; 8 remain after this review.

---

📝 Walkthrough

Walkthrough

ChatView now stores the last published composer overlay height. Scroll-to-end clearance updates reuse that height when showScrollToBottom changes instead of re-measuring the composer.

Changes

Composer clearance publishing

Layer / File(s)	Summary
Separate overlay measurement and clearance updates apps/web/src/components/ChatView.tsx	The composer stores its published overlay height, separates clearance publishing from timeline-inset publishing, and reuses the stored height when showScrollToBottom changes.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: t3dotgg

Merge Risk: ⚪ Minimal · up to fc368

The updated clearance flow preserves the published composer height when the scroll-to-end control changes visibility; no actionable merge risk remains.

🚥 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%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.	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 describes the primary change: preventing chat from jumping when the scroll-to-end pill mounts.
Description check	✅ Passed	The description includes the required What Changed, Why, UI Changes, and Checklist sections. It explains both changes and identifies the missing motion video evidence, but it is otherwise complete and…
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.

• Fix all pre-merge checks with AI

✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Commit to this branch
• Create a new PR

🧪 Generate unit tests (beta)

• Commit to this branch
• Create a new PR

---

_{Comment @coderabbitai help to get the list of available commands.}