Changes

;M2

:add/edit screens, only basic validation (e.g. non-empty) and address-field-specific merchant-provided errors

:FTU, data validation & error recovery, ready to enable on Nightly-only / Partner / End-to-end User Testing (not riding the trains)

:tab modal payment sheet, handling spec additions (e.g. retry, merchant field-specific errors, and new events) and UI bug fixes (not polish), gathering user testing and merchant feedback

;Later