{
  "protocol": "tar.a2a",
  "protocol_version": "1.0",
  "encoding": "application/json",
  "signature": "Ed25519 over canonical JSON",
  "identity": "public DID only",
  "timestamp": "ISO-8601 UTC Z",
  "schemas": [
    "message.schema.json",
    "task.schema.json",
    "error.schema.json"
  ]
}