feat: Add Tax, Billable, and Reimbursable selectors in the Split details page

[truph01]

Explanation of Change

• src/types/onyx/IOU.ts — Add taxCode?: string, taxAmount?: number, taxValue?: number to the SplitExpense interface.
• SplitExpenseEditPage.tsx — Add UI rows for Tax Rate, Reimbursable, and Billable (gated by the appropriate policy flags), navigating to the existing MONEY_REQUEST_STEP_TAX_RATE, MONEY_REQUEST_STEP_BILLABLE, and MONEY_REQUEST_STEP_REIMBURSABLE routes.
• SplitExpenseItems.ts (initSplitExpenseItemData) — Seed taxCode/taxAmount/taxValue from the parent transaction when initializing split items.
• SplitExpenseItems.ts (updateSplitExpenseField) — Carry taxCode/taxAmount/taxValue through from the draft transaction when saving a split edit.
• SplitTransactionUpdate.ts — Include taxCode/taxAmount/taxValue in the splits API payload and in the optimistic Onyx merge.
• SplitTransactionSplitsParam type — Add taxCode, taxAmount, taxValue fields.

Fixed Issues

$ #94038
PROPOSAL: #94038 (comment)

Tests

1. Create a workspace, enable tax > add a second tax rate + enable rules
2. Create an expense on the workspace
3. In the expense click More > Split
4. Open one of the splits
5. Verify: In the expense details of the split, the user should be able to set the tax rate on the individual split and set reimbursable/billable details.

• Verify that no errors appear in the JS console

Offline 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
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Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

[truph01]

@codex review

[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
src/libs/actions/IOU/SplitTransactionUpdate.ts	85.25% <ø> (ø)
src/libs/actions/IOU/SplitExpenseItems.ts	93.63% <0.00%> (-0.71%)	⬇️
src/pages/iou/SplitExpenseEditPage.tsx	0.00% <0.00%> (ø)
... and 40 files with indirect coverage changes

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Do not copy the full tax amount to every split

When a taxable expense is split into multiple new split expenses and the user saves without opening each tax row, every SplitExpense initialized here carries the original transaction's full taxAmount; the new updateSplitTransactions payload then sends that value for each split. For example, splitting an expense with $10 tax into two lines sends $10 tax on both child transactions, corrupting tax totals unless the user manually edits each one. This should be prorated/recomputed for the split amount or omitted until explicitly set.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

Keep optimistic split taxes in sync with the payload

These per-split tax fields are now sent to the API, but the optimistic transaction built later in this same function still uses originalTransactionDetails.taxCode/taxAmount/taxValue instead of the current splitExpense values. When a user changes a split's tax rate or tax amount and saves, offline mode and the immediate post-save UI/search state continue showing the original tax values until the server response arrives, which makes the new editor appear not to have saved the tax change locally.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

Remove transaction debug logging

This console.log runs on every render of the split details page and prints the full draft transaction, including merchant, amount, tax, report, and participant-related data, into production browser/native logs. Since this page is opened for real expenses, it leaks sensitive expense details and adds noisy render-time logging; remove the debug statement before shipping.

Useful? React with 👍 / 👎.