The app does not provision Square customers, so sending the local user ID as
customer_id in Create Card was rejected with CUSTOMER_NOT_FOUND, and filtering
List Cards by it returned nothing. reference_id is Square's free-form client
reference — max 128 chars, no uniqueness constraint — and is echoed in both
Create and List responses.
- Create Card payload: reference_id = local user ID (customer_id absent)
- List Cards: native ?reference_id=<userID> filter (no limit/customer_id,
no client-side filter, no cursor handling needed)
- Mock parity: CreateCardOnFile stores ReferenceID; GetCardsOnFile unchanged
- Regression guards: TestCreateCardOnFileHTTP_IdempotencyKey asserts
reference_id=user_1 and customer_id ABSENT; new
TestGetCardsOnFileHTTP_ReferenceIDFilter asserts the query shape