fix(mobile): the thread feed re-wraps once when an iOS column resizes#33459

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t3/legend-list-end-hold

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On iOS, opening, closing or dragging the Files inspector next to a thread changes the thread column's width. On a long thread the feed visibly broke: rows overlapped for several frames, then the feed jumped once or twice before landing at its end.

Two causes:

Rows re-wrapped before the list knew. The native column resize re-lays the feed's text at the new width immediately, but Legend List positions rows absolutely and only hears their new heights through onLayout. For ~4 frames, taller or shorter rows sat at their old offsets. In a split, ThreadFeed now pins the list to the width JS measured. Rows re-wrap in the render that hands the list its new width (extraData.viewportWidth), and Legend List measures them in that same commit.
The end landed a frame late. Even with a single re-wrap, Legend List's native MVCP kept the top visible row in place, and end following scrolled back to the end a frame later. The Legend List patch holds the end in the same pass while the feed is following it. #28125 dropped our older sizeChangeAnchor patch, which had covered this. It's small enough for Jay to upstream.

Neither change is enough on its own. With only the pinned width, the feed re-wraps once and then jumps about 35 pt a couple of frames later.

Evidence

iPhone Duo simulator, unfolded landscape, a long thread at its end, the stock main native client. Before is main; after is this branch. Each strip is consecutive 30 fps frames of the bottom of the thread.

Open Files: before and after

Drag the inspector divider: before and after

Close Files: before and after

All three at quarter speed, before above after: feed-reflow-before-after.mp4

Before: open shows 4 frames of overlapping rows, then a jump. The drag re-wraps at stale offsets and jumps twice. Close re-wraps wide, then narrow, with overlap between.
After: the feed keeps its old layout while the column moves (the inspector covers or uncovers its edge), then re-wraps once, already at its end, and stays put.

No test: the ThreadFeed change is visual and the other is a third-party patch, so the captures above are the proof.

🤖 Generated with Claude Code

Checks

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Added 1 commit22h ago

fix(mobile): the thread feed keeps its end through a pane resize on iOS6c2e2d7

MmacroscopeappBotreviewed · 1 inline thread22h ago

patches/@legendapp__list@3.7.2.patchline 14Outdated · 6c2e2d7Open thread

…	…	@@ -0,0 +1,80 @@
	11	+	+// anchored the top row, so the feed visibly jumps twice.
	12	+	+function shouldHoldEndOnSizeChange(ctx, dataChanged) {
	13	+	+ const state = ctx.state;
	14	+	+ return !dataChanged && !!state.props.maintainScrollAtEnd && !!state.didFinishInitialScroll && !state.endFollowInterrupted && !state.visibleContentAnchor && state.scrollingTo === void 0 && !state.isDragging && state.userScrollContentSize === void 0 && !!peek$(ctx, "isFollowingEnd");

MmacroscopeappBoton line 1422h ago

🟡 Medium patches/@legendapp__list@3.7.2.patch:14

When an existing final work-log row expands with maintainScrollAtEnd: { animated: false, on: { dataAppend: true } }, this predicate still replaces default MVCP with an adjustment to the new end, scrolling the list instead of preserving the visible position. The config object is truthy even though onItemLayout is normalized to false; check whether the trigger for adjustmentSource is enabled before holding the end, in both native builds.

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text

1	In file @patches/@legendapp__list@3.7.2.patch around line 14:
2
3	When an existing final work-log row expands with `maintainScrollAtEnd: { animated: false, on: { dataAppend: true } }`, this predicate still replaces default MVCP with an adjustment to the new end, scrolling the list instead of preserving the visible position. The config object is truthy even though `onItemLayout` is normalized to `false`; check whether the trigger for `adjustmentSource` is enabled before holding the end, in both native builds.

MmacroscopeappBot22h ago

Approvability

Verdict: Would Approve

Macroscope's review found this PR approvable — The change coordinates mobile feed reflow with list sizing and preserves end-following during size changes. Its exposure is limited to layout and scroll position; the reported work-log scrolling issue remains subject to the separate correctness gate.

Needs human approval because:

1 blocking correctness issue found at or above your repo's Minimum Blocking Severity

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CcoderabbitaiBot22h ago

Explain Change →

Walkthrough

The PR adds size-change end-following behavior to the patched Legend List package and changes how ThreadFeed measures and applies width in split layouts.

Changes: Thread feed end-following

Layer / File(s)	Summary
Size-change end-following `patches/@legendapp__list@3.7.2.patch`, `pnpm-workspace.yaml`	Both patched React Native builds adjust toward the content end for eligible size-only changes and retain the prior MVCP restoration as a fallback. The workspace maps `@legendapp/list@3.7.2` to the patch.
Split-layout viewport sizing `apps/mobile/src/features/threads/ThreadFeed.tsx`	ThreadFeed measures its outer viewport and applies the measured width to the list in split layouts when the width is positive.

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

Change: Bug fix

Possibly related issues

pingdotgg/t3code#31867: The issue reports an iOS end-following problem tied to isAtEnd. This PR changes size-only reflow handling, but the reported end-state calculation remains distinct.

Possibly related PRs

pingdotgg/t3code#31907: This PR changes LegendList end detection and end-follow re-arming, which determine whether the new size-change adjustment applies.
pingdotgg/t3code#33200: This PR changes ThreadFeed width-reflow anchoring and end-follow behavior, which are directly related to the current width measurement and reflow changes.
pingdotgg/t3code#28125: This PR changes ThreadFeed width-reflow handling and LegendList end maintenance, both related to the current changes.

Suggested labels: bugfix, 📱 Native Change

Suggested reviewers: shivamhwp

Merge Risk: External image Minimal · up to 7e05f

No confirmed merge-blocking issue remains. Verify the iOS resize behavior during normal testing.

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, the changes, and the simulator evidence. It does not provide the required scope and approval information or explain why this focused fix qualifies without prior a…	Add a link to the triaged issue or maintainer discussion with explicit approval of the direction and scope. If this qualifies as a small, focused fix of an obvious bug, explain why it needs no prior issue or discussion.

^Passed Passed checks: 3 passed

Check name	Status	Explanation
Title check	Passed	The title clearly describes the iOS thread-feed reflow fix during column resizing.
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.

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Add a link to the triaged issue or maintainer discussion with explicit approval of the direction and scope. If this qualifies as a small, focused fix of an obvious bug, explain why it needs no prior issue or discussion.

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CcoderabbitaiBotreviewed22h ago

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Added 2 commits21h ago

fix(mobile): the thread feed re-wraps once when an iOS column resizes838c8e8
Merge remote-tracking branch 'origin/main' into t3/legend-list-end-hold7e05f28

Ggithub-actionsBot20h ago

🚀 Expo continuous deployment is ready!

Project → t3-code
Platforms → android, ios
Scheme → t3code-preview

	🤖 Android	🍎 iOS
Fingerprint	78d2d1817402ec9fa9b5adfa3913c6c7e3b66970	4a37c4832042e11304dc24aba6144a6608d85d9b
Build Details	Build Permalink Details Distribution: `INTERNAL` Build profile: `preview:dev` Runtime version: `78d2d1817402ec9fa9b5adfa3913c6c7e3b66970` App version: `2.2.0` Git commit: `f19977522370d8b3d6f010ee193529de67a74515`	Build Permalink Details Distribution: `INTERNAL` Build profile: `preview:dev` Runtime version: `4a37c4832042e11304dc24aba6144a6608d85d9b` App version: `2.2.0` Git commit: `f19977522370d8b3d6f010ee193529de67a74515`
Update Details	Update Permalink Details Branch: `pr-33459` Runtime version: `78d2d1817402ec9fa9b5adfa3913c6c7e3b66970` Git commit: `f19977522370d8b3d6f010ee193529de67a74515`	Update Permalink Details Branch: `pr-33459` Runtime version: `4a37c4832042e11304dc24aba6144a6608d85d9b` Git commit: `f19977522370d8b3d6f010ee193529de67a74515`
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CcoderabbitaiBotreviewed20h ago

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