Bid Lifecycle

Buying a contract is the bid issuance action.

Sequence

1. Buyer calls POST /api/arbitration/contracts/buy with:
   • witness_proof
   • encrypted_witness_secret
   • witness_zkp
2. Contract is created in issued state.
3. Seller explicitly accepts via POST /api/arbitration/contracts/{id}/accept.
4. Accept response carries witness_secret_encrypted_for_seller.
5. Seller decrypts that value locally and calls POST /api/witness/replace to rotate custody to a fresh seller-held secret.
6. Contract proceeds with deliver/settlement transitions.

Fraud resistance

• Seller cannot claim acceptance never happened: acceptance is signed and stored.
• Seller cannot truthfully claim ownership without witness replacement evidence.
• Buyer cannot fake contract custody without valid current witness secret.