fix(web): stop mid-turn timeline overlap on streaming tool groups by macodev00 · Pull Request #12909 · pingdotgg/t3code

macodev00 · 2026-09-21T13:03:24Z

What

Keep streaming tool-group / live work rows from overlapping mid-turn by measuring expandable agent-spawn work-live rows (unpinned fixed size) and remasuring when spawn expand changes.

Why

Fixes #12094

Redo of closed #12734 addressing Macroscope Not-approved / Medium: mechanical LegendList sizing + expandedSpawnEntryIds in list extraData; avoid oversized layout policy rewrite.

UI

Desktop chat timeline: live agent-spawn expand should not overlap the following Working row.

Checklist

I read CONTRIBUTING.md and kept this small / bug-only
What + why explained above
Followed AGENTS.md documentation rules (no new docs)
No unrelated changes
CLA / AI-reviewed standing override for macodev00 auto-contrib

Summary by CodeRabbit

Bug Fixes
- Improved chat timeline behavior when new user messages appear during an active turn.
- Stabilized live activity group placement and identity across timeline updates.
- Improved timeline refreshing and row measurement when live groups or expanded agent activity change.
- Preserved accurate sizing for working, live activity, user, and expanded detail rows.
- Improved rendering consistency when agent-spawn activity expands or changes.
- Improved timeline performance and visual stability during updates.

Keep live tool-group identity across a steer so LegendList does not remount the row at the 90px estimate. Pin chrome sizes, leave agent-spawn work-live unpinned, and remasure via extraData when expanded groups grow or spawn details expand. Co-authored-by: maco <macodev00@users.noreply.github.com>

macroscopeapp · 2026-09-21T13:06:40Z

Approvability

Verdict: Approved at a58096c

Macroscope's review found this PR approvable — The PR makes a localized fix to existing web timeline virtualization: it preserves live-row identity and remasures variable-height streaming groups to prevent overlap. It adds focused regression tests without changing product defaults, APIs, security-sensitive code, or static-analysis settings.

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coderabbitai · 2026-09-21T13:10:36Z

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📥 Commits

Reviewing files that changed from the base of the PR and between 36a3b86 and cc75a2a.

📒 Files selected for processing (3)

apps/web/src/components/chat/MessagesTimeline.logic.test.ts
apps/web/src/components/chat/MessagesTimeline.logic.ts
apps/web/src/components/chat/MessagesTimeline.tsx

🚧 Files skipped from review as they are similar to previous changes (2)

apps/web/src/components/chat/MessagesTimeline.logic.test.ts
apps/web/src/components/chat/MessagesTimeline.logic.ts

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📝 Walkthrough

Walkthrough

The timeline keeps live activity rows stable across mid-turn steers. LegendList now uses row-specific fixed sizes and height signatures that include expanded activity and spawn content.

Changes

Timeline overlap and row sizing

Layer / File(s)	Summary
Live activity stability `apps/web/src/components/chat/MessagesTimeline.logic.ts`	Activity groups remain active when only user messages follow. Active live rows receive a stable identity.
Row sizing and height signatures `apps/web/src/components/chat/MessagesTimeline.logic.ts`	The timeline adds fixed heights for eligible rows. Expanded activity and agent-spawn rows remain measured. Extra-data signatures track expanded content and spawn expansion state.
LegendList integration and validation `apps/web/src/components/chat/MessagesTimeline.tsx`, `apps/web/src/components/chat/MessagesTimeline.logic.test.ts`	LegendList receives the computed row-size helper and extra-data value. The component uses a memoized view. Existing test assertions use named helpers without behavior changes.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: maria-rcks

Merge Risk: ⚪ Minimal · up to cc75a

The desktop timeline now preserves live-row identity and refreshes expanded-row measurements, addressing overlap during streaming without a remaining merge-blocking risk.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR meets the coding requirements in [`#12094`] and [`#12734`]. `MessagesTimeline.logic.ts` keeps live activity identity stable across mid-turn user messages. It includes expanded group entries and `ex…
Out of Scope Changes check	✅ Passed	The changes stay within [`#12094`] and [`#12734`]. They modify chat timeline projection, live-row identity, LegendList row sizing and refresh inputs, and focused timeline tests. These changes directly sup…
Docstring Coverage	✅ Passed	Docstring coverage is 87.50% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 24 functions across 3 files.
Title check	✅ Passed	The title clearly describes the primary fix: preventing mid-turn timeline overlap during streaming tool groups.
Description check	✅ Passed	The description explains the change, the reason, the affected UI behavior, and the issue reference. It is focused and mostly complete, although it uses shortened section headings and does not include …

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macodev00 · 2026-09-22T06:22:05Z

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macodev00 · 2026-09-22T06:23:35Z

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CodeRabbit requires 80% docstring coverage on functions this diff touches (was 38.46%). Comment the row projector, list owner, and steer fixtures instead of adding an internals page. Co-authored-by: maco <macodev00@users.noreply.github.com>

Lift the list owner out of memo, name extraData computation, replace the live-row .some() callback, and document steer fixtures so CodeRabbit coverage clears 80%.

macodev00 · 2026-09-22T06:35:45Z

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macroscopeapp · 2026-09-22T06:35:50Z

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macodev00 · 2026-09-22T06:36:57Z

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coderabbitai · 2026-09-22T06:42:33Z

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macodev00 · 2026-09-22T07:41:15Z

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macodev00 · 2026-09-22T08:31:25Z

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github-actions Bot added vouch:unvouched PR author is not yet trusted in the VOUCHED list. size:L 100-499 changed lines (additions + deletions). labels Sep 21, 2026

macroscopeapp Bot approved these changes Sep 21, 2026

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cursoragent and others added 2 commits September 22, 2026 06:31

docs(web): attach TSDoc to remaining timeline overlap functions

cc75a2a

Lift the list owner out of memo, name extraData computation, replace the live-row .some() callback, and document steer fixtures so CodeRabbit coverage clears 80%.

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