fix(web): stop mid-turn timeline overlap on streaming tool groups by macodev00 · Pull Request #12734 · pingdotgg/t3code

macodev00 · 2026-09-20T09:40:55Z

What

Keep live tool-group identity stable across a mid-turn steer so LegendList does not remount and place the next rows with a short estimate over a tall expanded details row.
Include expanded group entry counts in the height signature and pin fixed sizes for chrome rows (working, thinking, toggles, collapsed groups).

Why

Fixes #12094

A steer remounted the live tool group; the virtualizer then overlapped the mid-turn user message / Working-for pill on the streaming tool-call group.

UI

Desktop/web chat timeline: mid-turn user message and Working-for pill no longer overlap streaming tool groups.

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 layout and row sizing for more accurate positioning.
- Prevented overlaps between expanded activity details, steer messages, and working indicators.
- Improved stability of live activity rows as groups update or expand.
- Ensured timeline updates correctly as live work content grows.
- Improved handling of active work followed by user messages.
- Improved sizing for fixed, expanded, and agent-spawn activity items.
- Improved timeline refresh behavior when agent-spawn details are expanded.

A steer during a streaming expanded tool-call group remounted the live header under a new key, so LegendList placed the following user row and Working-for pill with a 90px estimate on top of a much taller details row. Keep the live-activity-row identity across that splice, pin chrome row sizes, and include an expanded-group height signature in list extraData so growing tool rows remasure before new tail rows are placed.

macroscopeapp · 2026-09-20T09:43:07Z

            renderItem={renderItem}
-            estimatedItemSize={90}
+            estimatedItemSize={TIMELINE_ESTIMATED_ITEM_SIZE}
+            getFixedItemSize={getFixedMessagesTimelineItemSize}


🟡 Medium chat/MessagesTimeline.tsx:1294

Opening a live agent-spawn row leaves LegendList using the fixed chrome height, so following rows are laid out over the expanded agent details. getFixedMessagesTimelineItemSize is applied to every work-live row even though AgentSpawnRow expands via expandedSpawnEntryIds; exclude expandable agent-spawn rows from fixed sizing (or remove this fixed-size path for them).

🤖 Copy this AI Prompt to have your agent fix this:

In file @apps/web/src/components/chat/MessagesTimeline.tsx around line 1294: Opening a live agent-spawn row leaves LegendList using the fixed chrome height, so following rows are laid out over the expanded agent details. `getFixedMessagesTimelineItemSize` is applied to every `work-live` row even though `AgentSpawnRow` expands via `expandedSpawnEntryIds`; exclude expandable agent-spawn rows from fixed sizing (or remove this fixed-size path for them).

macroscopeapp · 2026-09-20T09:44:15Z

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This production fix adds a sizable and subtle virtualized-layout policy affecting existing chat timeline rows, rather than making a small mechanical correction. An unresolved Medium finding also identifies possible overlap when live agent-spawn details expand while the row remains fixed-sized.

Not approved because:

1 blocking correctness issue found at or above your repo's Minimum Blocking Severity

^{Adjust the Minimum Blocking Severity for this repo — including turning it Off — in Settings. You can add or adjust custom eligibility rules. Learn more.}

coderabbitai · 2026-09-20T09:48:11Z

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

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📝 Walkthrough

Walkthrough

The timeline now preserves live-row identities, calculates fixed and estimated row sizes, derives row positions, and updates LegendList when expanded content changes. Tests cover expanded groups, agent-spawn rows, and overlap prevention.

Changes

Timeline layout

Layer / File(s)	Summary
Row sizing and overlap layout `apps/web/src/components/chat/MessagesTimeline.logic.ts`, `apps/web/src/components/chat/MessagesTimeline.logic.test.ts`	Added fixed-size resolution, bounded estimates, height signatures, row rectangle layout, overlap detection, and tests for expanded work groups. Agent-spawn rows remain measured when they can expand.
Live-row identity normalization `apps/web/src/components/chat/MessagesTimeline.logic.ts`	Active activity groups can continue before user messages. Duplicate live-row IDs now receive stable group-based IDs.
LegendList sizing integration `apps/web/src/components/chat/MessagesTimeline.tsx`	`LegendList` now uses derived extra data, the shared estimated item size, and fixed-size row resolution.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: maria-rcks

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The pull request satisfies the coding requirements in [`#12094`]. `MessagesTimeline.logic.ts` keeps live tool-group IDs stable across steers, updates height signatures as group entries grow, and exclude…
Out of Scope Changes check	✅ Passed	The changes stay within [`#12094`]. Timeline identity handling, virtualization sizing, layout helpers, agent-spawn remeasurement, and focused tests directly support the desktop timeline overlap fix. No …
Docstring Coverage	✅ Passed	Docstring coverage is 94.12% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 17 functions across 3 files.
Title check	✅ Passed	The title clearly identifies the web timeline overlap fix during streaming tool-group updates.
Description check	✅ Passed	The description explains what changed, why the change is needed, the affected UI, and the scope checklist. It is mostly complete, although it does not include the requested before/after screenshots fo…

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Inline comments:
In `@apps/web/src/components/chat/MessagesTimeline.logic.ts`:
- Around line 555-556: Update the "work-live" branch in the fixed-size
calculation to return undefined when row.entry.agentSpawn is present, allowing
AgentSpawnRow to be measured dynamically; retain the existing expanded and
collapsed heights for other work-live rows.

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

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CodeRabbit docstring coverage on the mid-turn tool-group fix was 33%. Add one-line TSDoc on every function in that diff so coverage clears 80%. Co-authored-by: maco <macodev00@users.noreply.github.com>

getFixedMessagesTimelineItemSize treated every work-live row as fixed chrome. Expanded AgentSpawnRow members grow in place via expandedSpawnEntryIds, so following rows overlapped. Leave expandable spawn work-live rows measured instead. Co-authored-by: maco <macodev00@users.noreply.github.com>

macodev00 · 2026-09-20T10:07:41Z

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coderabbitai · 2026-09-20T10:07:46Z

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macodev00 · 2026-09-20T10:50:49Z

@macroscope-app review

macroscopeapp · 2026-09-20T10:50:54Z

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macodev00 · 2026-09-21T06:28:07Z

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CodeRabbit docstring coverage on the mid-turn tool-group fix was 75%. Use function-declaration TSDoc on the test helpers and remaining touched functions so coverage clears 80%.

macodev00 · 2026-09-21T06:41:58Z

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coderabbitai · 2026-09-21T06:42:04Z

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getFixedMessagesTimelineItemSize returns undefined for work-live rows with agentSpawn so AgentSpawnRow is measured instead of pinned to chrome height. Include expandedSpawnEntryIds in LegendList extraData and derive the live spawn row in the overlap test.

macodev00 · 2026-09-21T07:56:04Z

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macodev00 · 2026-09-21T12:51:43Z

Closing to redo from scratch addressing Macroscope Not-approved feedback. Replacement READY PR coming (non-draft).

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 20, 2026

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Comment thread apps/web/src/components/chat/MessagesTimeline.logic.ts

macodev00 added 2 commits September 20, 2026 09:54

docs(web): add TSDoc on timeline overlap helpers

572458c

CodeRabbit docstring coverage on the mid-turn tool-group fix was 33%. Add one-line TSDoc on every function in that diff so coverage clears 80%. Co-authored-by: maco <macodev00@users.noreply.github.com>

docs(web): raise timeline overlap helper TSDoc coverage

42649b0

CodeRabbit docstring coverage on the mid-turn tool-group fix was 75%. Use function-declaration TSDoc on the test helpers and remaining touched functions so coverage clears 80%.

macodev00 closed this Sep 21, 2026

macodev00 mentioned this pull request Sep 21, 2026

fix(web): stop mid-turn timeline overlap on streaming tool groups #12909

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