fix(SDK-1284): persist 0 when an additional-earning field is cleared

[krisxcrash]

Fixes SDK-1284 (High, Pay v2 / RRoP Test Fest).

Correction to the ticket

The ticket attributes this to the gws-flows NumberInput adapter forwarding NaN. That component is not on this path. Additional earnings render as TextInputField type="number" min={0}, so the values are strings and NumberInput never enters the picture. No adapter change is needed; the cause is entirely in this component.

Root cause

buildCompensationFromFormData gated on formAmount !== '':

if (formAmount !== undefined && formAmount !== '') {

A cleared field is '', so the entry was skipped entirely and never added to updatedFixedCompensations. PayrollEditEmployee then spreads that object into the payrollUpdate, so the API received a fixed_compensations array with the entry absent — and the payroll update API leaves anything it is not sent untouched. The previously saved amount survived: the box looked empty, the save appeared to succeed, and the old value came back on refetch. That is exactly the reporter's "the pre and post are ultimately the same screenshot."

Typing an explicit 0 worked because that took the existingFixedCompensation branch and sent amount: "0".

Nothing caught it client-side either: the field is marked isRequired, but the schema is z.record(z.string(), z.string().optional()), so empty passes. (Field-level rules are ignored when a resolver is present, so isRequired is presentational here.)

Fix

An entry that already has a saved compensation now resolves a cleared field to '0', so clearing behaves exactly like typing 0 — the path testers already know works. Entries with no saved compensation stay omitted; there is nothing to zero out.

This also fixes the live gross-pay preview, which runs through the same builder, so the total drops the moment the field is cleared instead of showing the stale amount.

Testing

Two new cases in PayrollEditEmployeePresentation.test.tsx, sitting next to the existing "submits existing compensations even when set to zero":

• clearing an existing Bonus sends amount: '0' and leaves Commission untouched
• clearing an earning type that never had a saved amount still omits it

npx vitest run src/components/Payroll/PayrollEditEmployee — 70 pass. Both new tests also pass in isolation (-t), not just when an earlier test has warmed the i18n namespace. npm run tsc, eslint, prettier — clean.

Merge note

SDK-1285 touches the same file and the same schema/builder block. Whichever of the two merges second needs a small rebase there.