Workflow-driven skill that builds a refund test matrix from a payment-flow inventory: refund variants (full / partial / multiple-partials / over-refund / refund-on-disputed / refund-on-already-refunded), per-gateway nuances (Stripe, Adyen, PayPal, Braintree refund APIs), and timing variants (immediate / next-day / declined-by-bank), one test case per cell. Use for refund coverage on a new integration; for chargeback / dispute coverage use chargeback-flow-test-author, for webhook redelivery + idempotency use payment-webhook-replay, and for the state model use payment-flow-states-reference.