Agent Payment Mandate Cross-Protocol Mapper

Translates a payment mandate declared under one agentic-payment protocol (AP2, x402, or ACP) into another, by pivoting through one internal canonical schema instead of a pairwise table per protocol combination. The result is the translated mandate plus a mapping receipt — source digest, target digest, mapping-table version, and a declared lossy-fields list — so any field the source protocol could not carry is surfaced honestly rather than silently dropped. Nothing here initiates, routes, or settles a payment.