[WIP] [LegendList 2/7] fix: use list-aware message edit scrolling

[chrispader]

In expense views, message-edit scrolling currently assumes the main report action list is inverted. MoneyRequestReportActionsList orders items chronologically, so editing its newest message can ask the wrong list position to stay visible. This WIP extraction makes message-edit scrolling list-aware while preserving existing report behavior.

@roryabraham @dmkt9

Explanation of Change

The existing report action position context now carries both the action index and whether the action is newest, so each list declares its own ordering semantics. MoneyRequestReportActionsList also provides a separate list-level callback that scrolls to its newest position, while the inverted main report list keeps the existing report scroll manager fallback.

This is layer 2 of the seven-part LegendList series. Review order is #100732 → this PR → #100884 → #100733 → #100740 → #100734 → #100736. The branches are maintained with GH Stacks in the Margelo fork; because GitHub does not support linking cross-fork heads into an upstream Stack, each upstream PR targets Expensify/App:main and records the dependency order here.

Fixed Issues

$ #98994
PROPOSAL:

No approved proposal is linked.

Tests

1. Open an expense report with several report actions.
2. Edit and save the newest comment.
3. Verify the edited comment remains visible and the list stays at its newest position.
4. Edit an older comment and verify the list does not jump to its newest position.
5. Repeat the newest- and older-comment checks in a regular chat and verify its existing scroll behavior is unchanged.
6. Verify that no errors appear in the JS console.

• Verify that no errors appear in the JS console

Offline tests

1. Open a cached expense report, then go offline.
2. Edit the newest comment and verify it remains visible after saving.
3. Edit an older comment and verify the list does not jump to its newest position.
4. Return online and verify the pending edit synchronizes without changing the scroll position unexpectedly.

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 followed proper code patterns (see Reviewing the code)
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
  • I verified any copy / text that was added to the app is grammatically correct in English. It adheres to proper capitalization guidelines (note: only the first word of header/labels should be capitalized), and 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 followed the guidelines as stated in the Review Guidelines
• 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 a new CSS style is added I verified that:
  • A similar style doesn't already exist
  • The style can't be created with an existing StyleUtils function (i.e. StyleUtils.getBackgroundAndBorderStyle(theme.componentBG))
• 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.
• 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

Screenshots and videos are not included while this PR is WIP.

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Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-11T10:30:01.084468Z	a796f48	Draft marked ready

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[dylanexpensify]

Performance related vs pure product update. Input not needed