[chrispader]

Chat history still uses an inverted FlashList, while the remaining LegendList changes are spread across several PRs. I combined the patch refresh, chronological report-actions migration, and pagination loading on current main. The other list migrations remain in their own PRs.

Explanation of Change

This contains #106626, #100733, and #100740, layers 11-13 of the fifteen-part rollout. The earlier preparations, LegendList 3.7.2 upgrade, keyboard initial-state fix, and pagination write-order fix are already in the base. Chat selects the end anchor explicitly, and pagination supports Search transitions that finish immediately. The platform-specific list attributes and native action-sheet scroller stay at their shared boundary so they use the same list ref and positioning lifecycle.

Fixed Issues

$ Expensify#98994

Part of the migration split from Expensify#98270. No separate proposal is linked.

Tests

All platforms, chat history

1. Open a chat with several pages of history.
2. Scroll upward until older messages load. The loading indicator should clear without moving the message you were reading.
3. Choose Latest messages. The newest message should appear.
4. Send a message. It should appear at the end of the chat.
5. Scroll upward to read older messages.
6. Receive a message from another participant. The list should preserve your reading position.
7. Choose Latest messages. The received message should appear.

All platforms, linked messages

Start with a link to an older message in a long chat.

1. Open the message link. The linked message should be visible.
2. Scroll toward newer messages. Any pagination indicator should clear when its page loads.
3. Choose Latest messages. The list should reach the newest message.

All platforms, editing and recycled rows

1. Open a chat containing one of your messages and image or PDF attachments.
2. Open your message's action menu.
3. Choose Edit.
4. Replace its text with a multiline message.
5. Save the edit. The edited row should remain visible.
6. Scroll far enough to move the attachments off screen.
7. Scroll back to the attachments. Each preview should still belong to its message.
8. Open an attachment. Its image or document should match the preview.
9. Return to the chat. The same messages should remain visible.

• Verify that no errors appear in the JS console

Offline tests

1. Open a chat while online.
2. Disconnect the internet.
3. Reopen the chat. Cached messages should remain readable.
4. Send a message. It should appear locally.
5. Scroll to an unloaded edge. Existing messages should remain visible and no loading indicator should stay stuck.
6. Reconnect the internet. The message should send and history loading should work again.

QA Steps

Same as Tests and Offline tests.

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I verified any copy / text that was added to the app is either coming verbatim from figma or has been approved by marketing (in order to get marketing approval, ask the Bug Zero team member to add the Waiting for copy label to the issue)
• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
• If new assets were added or existing ones were modified, I verified that:
  • The assets are optimized and compressed (for SVG files, run npm run compress-svg)
  • The assets load correctly across all supported platforms.
• If the PR modifies code that runs when editing or sending messages, I tested and verified there is no unexpected behavior for all supported markdown - URLs, single line code, code blocks, quotes, headings, bold, strikethrough, and italic.
• If the PR modifies a generic component, I tested and verified that those changes do not break usages of that component in the rest of the App (i.e. if a shared library or component like Avatar is modified, I verified that Avatar is working as expected in all cases)
• If the PR modifies a component related to any of the existing Storybook stories, I tested and verified all stories for that component are still working as expected.
• If the PR modifies a component or page that can be accessed by a direct deeplink, I verified that the code functions as expected when the deeplink is used - from a logged in and logged out account.
• If the PR modifies the UI (e.g. new buttons, new UI components, changing the padding/spacing/sizing, moving components, etc) or modifies the form input styles:
  • I verified that all the inputs inside a form are aligned with each other.
  • I added Design label and/or tagged @Expensify/design so the design team can review the changes.
• If the PR adds or modifies the UI:
  • I asked an AI agent to review the changes for accessibility issues and addressed its findings.
  • I tested with a screen reader (VoiceOver on macOS) and verified all new/changed elements are reachable with a logical focus order.
  • I verified all new/changed elements have meaningful accessible names and roles.
  • I verified state changes are announced (e.g. checked/unchecked, expanded/collapsed, selected).
• I added unit tests for any new feature or bug fix in this PR to help automatically prevent regressions in this user flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.

Screenshots/Videos

These recordings are from the original migration and pagination PRs.

iOS: Native

Cold chat open and initial loading

FlashList is on the left and LegendList is on the right. FlashList leaves the report body blank during loading; LegendList shows the report-action skeleton before messages appear.

LegendListLoadingSkeletonVsFlashList.mp4

Cold expense-chat open

FlashList is on the left and LegendList is on the right. Both progress from the loading skeleton to an expense preview and its surrounding report actions.

ExpenseChatCold.mp4

Warm expense-chat open

FlashList is on the left and LegendList is on the right. Both open the cached expense preview and report actions from the inbox.

ExpenseChatWarm.mp4

Warm chat open

Side-by-side opens of the same cached chat, ending on the same report-action history. The implementations are not labeled in this recording.

LegendListWarmReportOpen.mp4

Android: Native

Cold chat open and initial loading

ColdOpenLoading.mp4

iOS: Native, pagination loading

LegendListPaginationIosFinished.mov

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