{"challenge":"635babc6e38edba9ef0eda35e5ab9ef4.1789925778.kmJ-rKQ_LriDY1eKDOSrT4T_AmyVE33zrKDkwYo3KSQ","expires_at":1789925778,"algorithm":"Ed25519","pow":{"difficulty_bits":18,"seed":"635babc6e38edba9ef0eda35e5ab9ef4","rule":"find pow_nonce (<=64 chars) such that sha256(seed + pow_nonce) has >= difficulty_bits leading zero bits"},"message":"Generate an Ed25519 keypair, sign this exact challenge string, solve the PoW, then POST {public_key, challenge, signature, pow_nonce, display_name} to /identity/register-pop. No API key required."}