fix(mobile): preserve chat rows when toggling commands

[juliusmarminge]

Expanding a command can briefly blank the entire mobile conversation and remount unrelated messages. This regressed in #10449, merged September 6 at 10:24 p.m. Pacific, when itemLayoutAnimation started switching between a transition and undefined. LegendList uses that presence to select its position and size component types, so a disclosure can replace the containers around the feed and replay row entrance animations.

Keep a zero-duration transition installed outside disclosure changes. The component types stay stable, ordinary updates remain immediate, and disclosures retain their existing transition.

Verified on an iOS 26.5 simulator with disposable showcase data. Expanding the same command remounted all five rendered rows on the base, including the unchanged user message and assistant answer; with this fix it remounted none. Temporary mount instrumentation was removed before the evidence captures. Repeated group and individual command expansion/collapse passed. Android shares this component but was not exercised separately.

Mobile typecheck, targeted lint and formatting passed. Lint reports existing warnings. All 29 tests in thread-feed-live-follow.test.ts and pending-thread-feed.test.ts passed.

Before: feed disappears during command expansion	After: conversation stays visible

Recording, before on the left and after on the right:

Before/after command expansion recording

Model: GPT-6. Harness: Codex.

Note

Preserve ThreadFeed row layout animation when toggling commands

• Adds THREAD_FEED_IMMEDIATE_TRANSITION, a zero-duration LinearTransition, to keep the LegendList item layout animation container mounted during ordinary feed updates.
• itemLayoutAnimation now uses the timed disclosure transition while disclosure is settling, and the zero-duration transition otherwise. Previously the prop became undefined outside disclosure settling, causing LegendList to swap component types, remount the feed, and replay row entrances.
• Risk: callers relying on the animation prop being undefined outside disclosure settling will see a zero-duration transition object instead.

^{Macroscope summarized a34b15c.}

Summary by CodeRabbit

• Bug Fixes
  • Improved thread feed updates by ensuring ordinary list changes appear immediately, while disclosure-related changes retain their existing animation behavior.

[macroscopeapp]

Approvability

Verdict: Approved at a34b15c

Macroscope's review found this PR approvable — This is a narrowly scoped mobile UI bug fix that stabilizes the LegendList animation configuration to preserve existing chat rows while retaining the intended disclosure animation. It introduces no new capability, schema change, product-default change, or static-analysis suppression.

^{You can add or adjust custom eligibility rules. Learn more.}

[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	13.6 KiB	13.6 KiB	−5 B (−0.0%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.0 KiB	7.0 KiB	+1 B (+0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.6 KiB	6.6 KiB	−6 B (−0.1%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.1 KiB	57.1 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.5 KiB	13.6 KiB	+52 B (+0.4%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.0 KiB	7.0 KiB	0 B (0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.5 KiB	+52 B (+0.8%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.8 KiB	57.9 KiB	+88 B (+0.1%)	66.4 KiB	✅
Claude	Live turn messages	8	10	+2 (+25.0%)	21	✅

Baseline: b717537 · PR result: a34b15c · 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: 113.9 KiB
• Claude decoded thread snapshot: 114.6 KiB

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

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Team

Run ID: 62076ec6-2956-4dd7-b3b0-3337d429360a

📥 Commits

Reviewing files that changed from the base of the PR and between b717537 and a34b15c.

📒 Files selected for processing (1)

• apps/mobile/src/features/threads/ThreadFeed.tsx

Included review availability: 4 reviews are currently available. Your included PR review attempts over the past 7 days set your current allowance at 10 reviews per hour.

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📝 Walkthrough

Walkthrough

The thread feed now applies a zero-duration LinearTransition to ordinary LegendList updates. Disclosure settling continues to use the existing animated transition.

Changes

Thread feed transitions

Layer / File(s)	Summary
Explicit item layout transitions apps/mobile/src/features/threads/ThreadFeed.tsx	Adds THREAD_FEED_IMMEDIATE_TRANSITION and applies it to ordinary updates. Disclosure settling continues to use THREAD_FEED_LAYOUT_TRANSITION.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Merge Risk: ⚪ Minimal · up to a34b1

Thread-feed updates now keep a stable immediate layout transition outside disclosure changes, preventing mobile conversation blanking and remounting while preserving disclosure animations. No current merge-blocking risk is identified.

Suggested reviewers: sunkenintime, t3dotgg, maria-rcks

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main fix: preserving mobile chat rows when users toggle commands.
Description check	✅ Passed	The description explains the problem, root cause, fix, verification steps, test results, UI impact, screenshots, and recording. It does not use the template headings or checklist format, but it provid…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 1…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch t3code/fix-legend-list-rerender

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