request_verification_challenge
Step 1 of wallet verification: get a fresh challenge for the user to sign. chain: "evm" or "solana". Pass agent_id (your marketplace identity) so the proof is bound to you. Present `challenge` to the user, have their wallet sign it (EVM personal_sign / Solana signMessage), then call verify_wallet_ownership with the returned `nonce` + signature. The challenge is single-use and expires (~10 min). Returns {challenge, nonce, expires_at}.
chainaddress必填agent_id