Credential components stored on a CarrierAccount. Deliberately a separate type from CarrierCortex's CarrierApiCredentialTypeCode, so the two subgraphs can compose without federation's identical-value-set rule for enums used in both input and output position. They are NOT independent: CarrierCortex converts values of its type into this one by name when it writes carrier accounts back, and ShipmentRating converts this type into CarrierCortex's when it rates (RatingRequest). A value added to either side MUST be added to the other -- CarrierCortexDgs api/src/main/resources/com/zonos/schema/enums.graphqls -- or those conversions throw IllegalArgumentException at runtime. Nothing checks this at build time.