fix(mobile): only make work rows expandable when the body adds something

[juliusmarminge]

Stacked on #10209.

Problem

Every work row with a command or detail got a chevron, so runtime warnings, background-task summaries, and short commands opened to repeat the one line they already showed. Web only marks a row expandable when its body adds something beyond the visible label (PlainWorkEntryRow.canExpand); mobile checked field presence.

Fix

Decide canExpand against the collapsed label the row actually renders (workEntryRowLabel, now shared between the feed model and ThreadWorkLogRow so they cannot drift). Multi-line bodies stay expandable because the collapsed row truncates them to one line; MCP payloads and changed-file lists always do. Cheap field checks run first so large tool outputs are not serialized per row (the existing deferred-expansion test guards that).

Verification

• vp test run apps/mobile/src/lib/threadActivity.test.ts — 95 passed, with new cases for a task summary that is its own detail, a runtime warning, a multi-line task report, and a command whose output differs from the command.
• tsc --noEmit for apps/mobile, targeted lint and format.
• Simulator, same seeded group on main and this branch: the "Run mobile threadActivity tests" and "git status --short" rows lose their chevrons; the multi-line ffmpeg command and the file read keep theirs.

Implemented by Claude Fable 5 in the Claude Code harness.

[macroscopeapp]

Approvability

Verdict: Approved at e4d0f1d

Macroscope's review found this PR approvable — This is a small, self-contained mobile work-log bug fix that removes expansion only when no additional content exists, while preserving expansion for multiline or otherwise distinct output. The behavior is covered by focused tests and does not affect schemas, configuration, or other sensitive production concerns.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	13.6 KiB	—	15.1 KiB	✅
Codex	Thread snapshot wire	—	7.0 KiB	—	7.3 KiB	✅
Codex	Live turn WebSocket wire	—	6.6 KiB	—	7.8 KiB	✅
Codex	Live turn WebSocket decoded	—	57.1 KiB	—	66.4 KiB	✅
Codex	Live turn messages	—	10	—	21	✅
Claude	Total thread wire	—	13.6 KiB	—	15.1 KiB	✅
Claude	Thread snapshot wire	—	7.0 KiB	—	7.3 KiB	✅
Claude	Live turn WebSocket wire	—	6.6 KiB	—	7.8 KiB	✅
Claude	Live turn WebSocket decoded	—	57.9 KiB	—	66.4 KiB	✅
Claude	Live turn messages	—	10	—	21	✅

Baseline: unavailable · PR result: e4d0f1d · 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: 113.8 KiB
• Claude decoded thread snapshot: 114.5 KiB

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