fix(clients): running subagent cards stay visible after their parent turn settles

[juliusmarminge]

Closes #16621.

Problem

A subagent can keep working after the turn that launched it settles. The "Waiting on N subagents" footer counts it, but its card folded away under "Worked for", so the thread showed nothing for the work the footer said it was waiting on. This happened for app-owned children (delegate_task) and provider-native ones alike.

This is a regression. #11474 kept subagent rows out of turn folds. The V2 orchestrator merge (#2829) rewrote the fold logic and that exception didn't come over. The only remaining test covered a finished child, so nothing failed.

Fix

A subagent card stays outside its turn's fold while its own status is active. The check is isOrchestrationV2WorkActive, the same one the footer uses, so the card and the footer always agree. Finished children still fold as before.

• Shared check: isLiveSubagentTurnItem in packages/client-runtime/src/state/subagentRuntime.ts, used by both clients.
• Web (MessagesTimeline.logic.ts): live cards stay out of the "Worked for" fold and the "Superseded attempt" fold. A steer supersedes the attempt but doesn't stop its children, so that fold hid live children too. Adjacent cards from the same run and provider turn render as one grouped row, so that group stays visible while any member is live and is never shown half folded.
• Mobile (threadActivity.ts): an activity group with a live subagent stays visible.

The footer and the server are unchanged.

Before and after

The same live thread on one dev server: a Claude parent launched a background subagent that is still working after the turn settled.

Before (main): the footer says it is waiting on the subagent, but there is no card.

After (this PR): the running card stays visible next to the footer that counts it.

Verification

• New fold tests in MessagesTimeline.logic.test.ts: a running app-owned child, a running provider-native child, a mixed group (one done, one running), and a running child of a superseded attempt all stay visible while the turn's other settled work still folds. Completed and failed children still fold. Mobile has the equivalent case in threadActivity.test.ts. All five new live-child tests fail on main.
• vp test run on both files: 230 passed. tsc --noEmit for web, mobile and client-runtime, plus vp lint and vp fmt --check on the changed files, are clean.
• Reviewed by GPT 6.1 Sol and Fable 5.1. Both traced every provider's subagent status path against the footer's and found no case where the card and the footer disagree.
• Not checked: the mobile client in a simulator.

Model and harness: Claude Opus 5.5, Claude Code in T3 Code.

🤖 Generated with Claude Code

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ℹ️ Recent review info

⚙️ Run configuration

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📥 Commits

Reviewing files that changed from the base of the PR and between 611132c and a6ec641.

📒 Files selected for processing (5)

• apps/mobile/src/lib/threadActivity.test.ts
• apps/mobile/src/lib/threadActivity.ts
• apps/web/src/components/chat/MessagesTimeline.logic.test.ts
• apps/web/src/components/chat/MessagesTimeline.logic.ts
• packages/client-runtime/src/state/subagentRuntime.ts

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📝 Walkthrough

Walkthrough

The change adds a runtime predicate for active subagent turn items and uses it to keep live subagent activity visible when parent-turn activity is folded in the web and mobile timelines.

Changes

Subagent visibility

Layer / File(s)	Summary
Identify live subagent items packages/client-runtime/src/state/subagentRuntime.ts	Adds isLiveSubagentTurnItem, which returns true for active subagent turn items.
Preserve live subagent batches in the web timeline apps/web/src/components/chat/MessagesTimeline.logic.ts, apps/web/src/components/chat/MessagesTimeline.logic.test.ts	The timeline groups adjacent subagent events with matching run and provider-turn IDs. If any item in a batch is active, the batch stays visible during turn and superseded-attempt folding. Tests cover active, completed, and failed children.
Preserve live subagent activity in the mobile timeline apps/mobile/src/lib/threadActivity.ts, apps/mobile/src/lib/threadActivity.test.ts	Run folding retains activity groups containing a live subagent item. Tests cover active batches and completed-only subagents.

Priority: ➖ Normal

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

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: t3dotgg

Merge Risk: ⚪ Minimal · up to a6ec6

Running subagent cards now stay visible after their parent turn settles, while finished children still fold as before. No merge-blocking risk was identified. The mobile client was not checked in a simulator, which is a normal validation gap.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise, uses the conventional commit format, and clearly identifies the primary fix: keeping running subagent cards visible after the parent turn settles.
Description check	✅ Passed	The description covers the problem, expected behavior, implementation across web and mobile, linked issue, screenshots, focused tests, type checks, linting, formatting, and the simulator limitation. I…
Linked Issues check	✅ Passed	Issue #16621 requires live app-owned child cards to remain visible after the parent run settles, while settled parent work remains foldable and each child retains its status. The shared `isLiveSubagen…
Out of Scope Changes check	✅ Passed	The changes are limited to shared subagent lifecycle detection, web and mobile fold behavior, and focused automated tests. Provider-native coverage, grouping behavior, and the shared helper directly s…

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[macroscopeapp]

Approvability

Verdict: Approved at a6ec641

Macroscope's review found this PR approvable — This is a narrowly scoped client-side bug fix that keeps active subagent cards visible while their parent turn folds, with completed and failed children retaining existing behavior. The shared status check and targeted web/mobile regression tests keep the runtime impact contained and verifiable.

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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: 611132c · PR result: a6ec641 · 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.