FullStateRequest
@Serializable
@SerialName(value = "fullStateRequest")
Sent by requester when a RootDigest from sender disagreed with its own root: please ship the state. The recipient answers with a FullState.
Honored only when the recipient has sent requester a RootDigest since the last request it honored, which caps delivery at one full state per peer per anti-entropy interval — exactly the pre-#1955 ceiling — and makes an unsolicited request a no-op.