Fix infinite loading after cross-report expense merge

[MelvinBot]

Explanation of Change

When merging expenses across different reports (cross-report merge), the target transaction's reportID was not being optimistically updated to the destination report. After the merge, the UI navigated to the destination report, but from Onyx's perspective the transaction still belonged to its original report. This caused MoneyRequestView to find no valid transactionThreadReport, triggering its skeleton guard at MoneyRequestView.tsx:789 and displaying infinite loading.

Additionally, if the source report was a single-expense report that also happened to be the merge destination, it would be optimistically deleted (SET to null) even though the backend would keep it with the merged expense. This compounded the issue by making the destination report appear as null in Onyx.

This PR makes two changes to src/libs/actions/MergeTransaction.ts:

1. Pass newTransactionReportID to getUpdateMoneyRequestParams when the destination report differs from the target transaction's current report. This leverages the existing newTransactionReportID parameter (already used in the Split flow) to optimistically update the target transaction's reportID to the destination report, so the derived data and component chain reflect the correct state immediately.

2. Skip optimistic deletion of the source report when it is the merge destination. The backend will move the merged transaction to that report, so it should not be deleted optimistically.

Fixed Issues

$ #79717
PROPOSAL: #79717 (comment)

Tests

1. Go to staging.new.expensify.com
2. Go to a workspace chat
3. Create two reports with one expense in each report (Report A, Report B)
4. Open Report A
5. Click More > Merge
6. Select expense from Report B > Continue
7. Select the second option for each detail > Next
8. Click Merge expenses
9. Verify the report loads correctly (no infinite loading)
10. Go back to workspace chat
11. Create another report with an expense (Report C)
12. Open Report C
13. Click More > Merge
14. Select expense from the other report > Continue
15. Select the second option for each detail > Next
16. Click Merge expenses
17. Verify the report loads correctly after the second merge (no infinite loading)

• Verify that no errors appear in the JS console

Offline tests

1. While offline, attempt the merge flow described above
2. Verify the optimistic data renders correctly (no infinite loading/skeleton)
3. Go back online and verify the data syncs properly

QA Steps

Same as Tests above. The key verification is step 17 — the second cross-report merge should no longer cause infinite loading.

• 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
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Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

[situchan]

@MelvinBot close PR. Do you know which PR fixed the original bug?

[MelvinBot]

Closing this PR as requested — the linked issue (#79717) is no longer reproducible (confirmed by QA on build 9.3.43-1) and was closed by mallenexpensify.

Which PR fixed the original bug? There is no single PR that directly targeted #79717. The bug was most likely resolved as a side effect of one or more of these merge-related PRs that landed between when the issue was filed and when QA confirmed it was fixed:

• #72990 — "Report turns to skeleton loader after merging expenses offline" (merged 2026-02-11) — Most likely candidate, as it directly addresses the skeleton loader symptom after merging expenses
• #82006 — "Refactor mergeTransaction function to pass selfDMreport" (merged 2026-02-11) — Refactored the merge transaction logic
• #79766 — "Fix incorrect chat opening after merging expense with self DM" (merged 2026-02-23) — Fixed merge navigation issues

My best guess is #72990 since it fixed the same symptom (skeleton/infinite loading after merge) in a closely related scenario.