Fix: preserve prev/next carousel arrows when opening an expense from an expense report

[MelvinBot]

Explanation of Change

The prev/next carousel arrows in the expense RHP are driven by a single shared Onyx key (TRANSACTION_THREAD_NAVIGATION_TRANSACTION_IDS). When the full expense-report view (MoneyRequestReportView) mounts on top of an existing transaction thread, its effect in MoneyRequestReportTransactionList seeds that key with the report's own transactions and registers an unmount cleanup that calls clearActiveTransactionIDs().

That effect already guards against taking over a descriptor-backed carousel (the Home "Recently added" flow) so it doesn't clobber the carousel of the thread sitting underneath it. But the Spend page seeds the carousel with a search snapshot hash and no descriptors (setActiveTransactionIDs(siblingTransactionIDs, hash)), so this guard didn't cover it. As a result, opening an expense from the Spend page → clicking the report subtitle link → backing out overwrote and then cleared the Spend-page carousel, dropping the list below 2 items so the arrows disappeared.

This fixes it by extending the existing guard to also bail when a snapshot-backed carousel is active, mirroring the descriptor handling:

• getActiveTransactionIDs() now also returns the active snapshotHash.
• The MoneyRequestReportTransactionList effect returns early (registering no cleanup) when either a snapshot hash or descriptors are present, so it never clobbers the underlying Spend-page carousel. Row presses inside the report still re-seed the correct siblings lazily via useNavigateToTransactionThread.

Fixed Issues

$ #96545
PROPOSAL:

Tests

1. Go to Spend > Expenses (a workspace with at least two expenses).
2. Open any expense → verify the prev/next arrow buttons appear on the expense RHP.
3. Click the subtitle link under the report title to open the expense report.
4. Open any expense from that report.
5. Click the report RHP back button twice.
6. Verify the prev/next arrow buttons are still shown on the expense RHP (they no longer disappear).

• Verify that no errors appear in the JS console

Offline tests

Same as tests.

QA Steps

Same as 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

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

[MelvinBot]

I created this PR from an upstream branch since I don't have push access to your fork.

To take ownership of this branch and be able to push updates, run:

git remote add upstream https://github.com/Expensify/App.git
git fetch upstream claude-fixExpenseCarouselArrowsDisappear
git checkout -b claude-fixExpenseCarouselArrowsDisappear upstream/claude-fixExpenseCarouselArrowsDisappear
git push -u origin claude-fixExpenseCarouselArrowsDisappear

Then you can close this PR and open a new one from your fork.

[codecov]

Codecov Report

❌ Looks like you've decreased code coverage for some files. Please write tests to increase, or at least maintain, the existing level of code coverage. See our documentation here for how to interpret this table.

Files with missing lines	Coverage Δ
...stReportView/MoneyRequestReportTransactionList.tsx	0.55% <0.00%> (-0.01%)	⬇️
src/libs/actions/TransactionThreadNavigation.ts	71.42% <0.00%> (ø)
... and 10 files with indirect coverage changes

[MelvinBot]

🤖 I looked into the failing checks — there's no code fix to push.

The only failing check is PR Author Checklist / checklist, and it's failing simply because the checklist boxes in the PR description aren't ticked:

You completed 0 out of 38 checklist items with 38 unfinished items

That's a human-only checklist — it needs the author/reviewer to check the boxes, so I can't complete it for you.

Every actual CI check is green: typecheck, ESLint check, all 8 test jobs, Bun tests, Storybook tests, Check for unused styles, and Compare knip issues against main all passed. The baseline-perf-tests / branch-perf-tests jobs are still running but aren't failures.

Next step: tick the boxes in the PR Author Checklist section of the description and the checklist check will pass.