[Bug]: Thread details side-tabs (Subagents/Lineage/Automations/Background Tasks) disappear once rows populate #15304

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1. juliusmarminge commented on Oct 3, 2026

   

   juliusmarminge

   on Oct 3, 2026

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   Grok responding on behalf of Julius.

   Triage

   Thanks for the detailed report, @tarunravi! I can confirm this on main at 71dbaf1. The sections really are being folded away, not failing to mount.

   ThreadDetailsPanel only renders two of these blocks when density === "full" and the thread isn't a draft:

   • ThreadAutomationsPanel at apps/web/src/components/chat/ThreadDetailsPanel.tsx:225
   • ThreadRelationshipsPanel at apps/web/src/components/chat/ThreadDetailsPanel.tsx:229

   So there are two gates rather than four. This card has no separate Background Tasks section, and Subagents are rows inside the single Lineage section (ThreadRelationshipsControl). Both panels return null until they have rows, which is why their headings don't show while they're empty.

   ThreadDetailsCard starts at full while the measured full height is still 0. Once the measured full tree is taller than the card, resolveThreadDetailsCardDensity in threadDetailsCardLayout.ts steps down to compact. The card's max height is the canvas height minus 24px, or less when the preview overlaps it. Populated Lineage is capped (max-h-[13.5rem], with its own scroller), but Lineage plus Automations still sits on top of Workspace and Version Control, and on a ~800px window that total can be taller than the card. The new rows paint at full, the ResizeObserver records the taller height, and data-density flips to compact, which unmounts the same panels.

   That full height is cached per environmentId:threadId:card width and isn't measured again while the card is compact, because those panels aren't mounted then. A taller window or a wider card can bring full back. Losing the rows that caused the overflow can't, because the cached height still fails the fit check.

   The ScrollArea doesn't help here, because density is picked so the tree fits before that viewport ever scrolls.

   Likely fix area

   • One option is to keep Automations and Lineage mounted below full, let the existing card scroll, and remeasure when their rows change.
   • Removing every density === "full" check would reach further than this bug. The environment selector and workspace branch controls are folded on purpose, and threadDetailsCardLayout.test.ts covers that compact and essential folding.

   A maintainer will decide on the fix direction.
2. juliusmarminge

   added

   bugSomething is broken or behaving incorrectly.Something is broken or behaving incorrectly.

   via-triageFiled through npx t3 triageFiled through npx t3 triage

   on Oct 3, 2026
3. fyzanshaik commented on Oct 3, 2026

   

   fyzanshaik

   on Oct 3, 2026

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   Opened PR #15348 for the Previous agents expansion trigger described here.

   Expanding the completed-agent list overwrote the card's fitting measurement with the taller content, which selected compact density and unmounted Lineage. The patch keeps a stable minimum measurement for density decisions and retains the latest expanded height separately so the floating preview still clears the real card.

   Verified with 16 completed agents in the T3 Browser panel: in a 420px-tall chat canvas, the card remains 396px tall and Lineage stays mounted; showing all 16 agents produces a scrollable list. The PR includes before/after screenshots, a recording, and focused regression coverage.

   This addresses expansion after the collapsed card has been measured. It preserves intentional folding when available space drops and does not claim to resolve every initial-population scenario in this issue.
4. juliusmarminge commented on Oct 7, 2026

   

   juliusmarminge

   on Oct 7, 2026

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   Grok responding on behalf of Julius.

   This should be fixed by #16635, which just merged to main. Lineage is no longer counted when the card picks its density, so populating or expanding Lineage rows doesn't flip the card to compact and unmount the section anymore. The expanded rows now use the existing scroll areas. If Automations rows still fold the card on a current build, comment here and we'll reopen.
5. juliusmarminge

   closed this as completedon Oct 7, 2026