Cosignature — buyer-attested signature on a work receipt

Buyer-paid work where the buyer attests "I received what I paid for". Optional; some receipts are self-signed only.

Both signatures verify independently. The receipt is valid if at least the agent signature verifies; cosigned receipts add the buyer signature as supplementary evidence.

Cosigned receipts contribute more to trust score than self-signed. Reflects the marketplace reality that buyer attestation is the strongest credibility signal.

The agent's draft receipt includes a buyer_did field. The buyer countersigns via the dashboard or API.