fix(mobile): retain resting scroll offsets through Duo inset changes #22978 · pingdotgg/t3code

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Approvability

Verdict: Needs Human Approval

Macroscope's review found this PR requires human approval — This PR changes scrolling behavior across several mobile screens and adds timing-sensitive feed reflow restoration around LegendList measurement, including deferred and imperative scroll operations. The added tests cover the pure anchoring and offset logic, but the production interaction paths remain sufficiently complex to merit focused review.

No code changes detected at 84df3e9. Prior analysis still applies.

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📒 Files selected for processing: 10

apps/mobile/src/features/home/HomeScreen.tsx
apps/mobile/src/features/pull-requests/PullRequestReviewersScreen.tsx
apps/mobile/src/features/pull-requests/PullRequestRouteScreen.tsx
apps/mobile/src/features/pull-requests/PullRequestsScreen.tsx
apps/mobile/src/features/threads/ThreadFeed.tsx
apps/mobile/src/features/threads/thread-feed-live-follow.test.ts
apps/mobile/src/features/threads/thread-feed-live-follow.ts
apps/mobile/src/native/useRestingTopOffset.test.tsx
apps/mobile/src/native/useRestingTopOffset.ts
apps/mobile/vite.config.ts

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📝 Walkthrough

The mobile app adds a hook for maintaining resting top offsets in scroll views. The thread feed also captures and restores its end or visible-row position when viewport width changes cause rows to remeasure.

Changes: Resting top offset

Layer / File(s)	Summary
Offset hook and validation `apps/mobile/src/native/useRestingTopOffset.ts`, `apps/mobile/src/native/useRestingTopOffset.test.tsx`, `apps/mobile/vite.config.ts`	The hook manages a held top offset and forwards scroll events. Tests cover inset changes, scrolling, and restored positions.
Scroll-view adoption `apps/mobile/src/features/home/HomeScreen.tsx`, `apps/mobile/src/features/pull-requests/PullRequestReviewersScreen.tsx`, `apps/mobile/src/features/pull-requests/PullRequestRouteScreen.tsx`, `apps/mobile/src/features/pull-requests/PullRequestsScreen.tsx`	Home and pull-request scroll views use the hook instead of fixed top-inset content offsets. The pull-request list no longer sets an initial scroll offset.

Thread-feed reflow

Layer / File(s)	Summary
Reflow anchors and scroll resolution `apps/mobile/src/features/threads/thread-feed-live-follow.ts`, `apps/mobile/src/features/threads/thread-feed-live-follow.test.ts`	New helpers represent end or visible-row anchors and calculate corrected offsets. Tests cover end-following, proportional row positions, and unavailable anchors.
Feed reflow and restoration `apps/mobile/src/features/threads/ThreadFeed.tsx`	ThreadFeed captures anchors during width changes and restores them after a settling delay. User interaction and thread state changes cancel restoration.

Priority: ➖ Normal

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

Change: Bug fix

Sequence Diagram(s)

mermaid

1	sequenceDiagram
2	participant ThreadFeed
3	participant resolveThreadFeedReflowAnchor
4	participant FeedList
5	participant resolveThreadFeedReflowScroll
6	ThreadFeed->>resolveThreadFeedReflowAnchor: Capture end or visible-row anchor
7	ThreadFeed->>FeedList: Update viewport width and remeasure rows
8	ThreadFeed->>resolveThreadFeedReflowScroll: Resolve anchor after settling delay
9	resolveThreadFeedReflowScroll-->>ThreadFeed: Return corrected scroll offset
10	ThreadFeed->>FeedList: Restore anchored position

Possibly related issues

pingdotgg/t3code#12372: The issue concerns restoring the thread viewport after content changes, which overlaps with this PR’s width-driven row remeasurement and position restoration.

Suggested reviewers: maria-rcks, t3dotgg

Merge Risk: ⚪ Minimal · up to 26a16

No actionable merge-blocking issue was identified in this change; it is ready for normal checks.

Pre-merge checks: ^Passed 3 · ^Failed 1

^Failed Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Description check	Warning	The description explains the problem, implementation, verification results, known limitations, recordings, and restack details. It does not provide the required section structure or the required scope…	Organize the description under Problem, Change, Scope and approval, and Verification headings. Add the triaged bug or discussion link with explicit maintainer approval, or explain why this focused fix qualifies for an exemption. Keep the ex…

^Passed Passed checks: 3 passed

Check name	Status	Explanation
Title check	Passed	The title clearly and concisely describes the main mobile change: preserving resting scroll offsets during Duo inset changes.
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.

Full details: Description check

Explanation

The description explains the problem, implementation, verification results, known limitations, recordings, and restack details. It does not provide the required section structure or the required scope and approval evidence, such as a triaged issue or explicit maintainer approval.

Resolution

Organize the description under Problem, Change, Scope and approval, and Verification headings. Add the triaged bug or discussion link with explicit maintainer approval, or explain why this focused fix qualifies for an exemption. Keep the existing test results, observed limitations, screenshots, and recordings in the Verification section.

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fix(mobile): retain resting scroll offsets through Duo inset changes#22978

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Sequence Diagram(s)