fix(web): toggling tools and thinking at the bottom keeps you at the bottom

[t3dotgg]

When you were at the bottom of a thread and opened a tool group, a tool row, or the thinking/turn fold, the new content opened below and you were no longer at the bottom. Closing one at the bottom left you about 8px above the bottom.

Every disclosure toggle turned off "stick to bottom" and held the toggled row in place, even when you were at the end. Now, if you are at the end when you toggle, the list stays pinned to the bottom while the rows re-measure. Tool output that renders a few frames late is pinned before it paints. If you are scrolled up, nothing changes: the toggled row holds its place.

Before	After
📹 screen recording	📹 screen recording

The badge shows the distance from the bottom. Before: 192px, 96px, and 8px after toggles. After: 0px.

Verified in the web app with real thread data. A sampler read the distance from the bottom right before each paint. On main, expanding left 282 to 1065px gaps. With this change it was 0px on every frame across 16 toggles (turn fold, tool groups, single tool rows, open and close). It also stays at the bottom during a running turn. Not at the bottom, the toggled row stays at the same spot.

Reviewed with sol-loop: 2 rounds with GPT-6.1-Sol on high.

Created with Claude Opus 5.5 in Claude Code.

[macroscopeapp]

Approvability

Verdict: Approved at 93e8412

Macroscope's review found this PR approvable — This is a contained web bug fix that keeps the conversation timeline pinned only when a disclosure toggle starts at the end, while preserving the existing position for users who are scrolled up. The added tests cover both positioning modes and delayed row resizing.

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[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	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Codex	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Codex	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Codex	Live turn WebSocket decoded	20.9 KiB	20.9 KiB	0 B (0.0%)	29.3 KiB	✅
Codex	Live turn messages	2	2	0 (0.0%)	8	✅
Claude	Total thread wire	5.0 KiB	5.0 KiB	0 B (0.0%)	6.8 KiB	✅
Claude	Thread snapshot wire	3.8 KiB	3.8 KiB	0 B (0.0%)	4.9 KiB	✅
Claude	Live turn WebSocket wire	1.2 KiB	1.2 KiB	0 B (0.0%)	2.0 KiB	✅
Claude	Live turn WebSocket decoded	21.2 KiB	21.2 KiB	0 B (0.0%)	29.3 KiB	✅
Claude	Live turn messages	2	2	0 (0.0%)	8	✅

Baseline: 4772822 · PR result: 93e8412 · 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: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

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

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Path: .coderabbit.config.ts
• Review profile: CHILL
• Plan: Team
• Run ID: 6b9d13ca-9256-46a4-b67e-a2765dab4565

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📥 Commits

Reviewing files that changed from the base of the PR and between 4772822 and 93e8412.

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📒 Files selected for processing (2)

• apps/web/src/components/chat/MessagesTimeline.test.tsx
• apps/web/src/components/chat/MessagesTimeline.tsx

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📝 Walkthrough

Walkthrough

Tool-output disclosure toggles now pin the timeline to the end when the toggle begins there. Row-size changes reschedule settling. Tests cover scroll behavior at and away from the end.

Changes

Disclosure scroll behavior

Layer / File(s)	Summary
Disclosure settling and row-size updates apps/web/src/components/chat/MessagesTimeline.tsx, apps/web/src/components/chat/MessagesTimeline.test.tsx	Disclosure settling pins the timeline to the end when a toggle begins there. Elsewhere, visible-content restoration remains enabled except for the disclosure anchor row. Row-size changes reschedule settling and continue to report content overflow. Tests verify scroll position after expansion and collapse at and away from the end.

Priority: ⬇️ Low

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

Change: Bug fix

Suggested reviewers: juliusmarminge

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Merge Risk: ⚪ Minimal · up to 93e84

The disclosure scroll change is mergeable after normal checks; no blocking behavior was established.

Pre-merge checks | 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: keeping the timeline pinned to the bottom when tools or thinking are toggled at the end.
Description check		The description clearly explains the problem, implementation, verification results, screenshots, recordings, and agent usage. It does not include an explicit Scope and approval section or explain why …
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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