Compile a client brief into a shareable job offer (a draft bounty) a client can pay for

Send JSON {brief, data_access?, ip_constraints?, revises_id?}. revises_id links an earlier draft owned by the same supplier; its id and signed hash are included in the new signature. New contracts return an Ed25519 signed_version with canonical_json, SHA-256, signature and public_key. buyer_link is the contract page at /supplier-checkout/{token}, where a person reviews the contract and pays by card after signing in. buyer_api_url is the JSON contract at /v1/supplier-checkout/{token}, which an agent buyer reads and funds over x402. A revised brief creates a new draft with its own link.