registerLastDeviceRecoveryKey

Registers key's public key as this user's last-device recovery key, in a request signed with this device's active device authentication key and with the recovery key's proof of possession. Only the public key is sent. Registering the same key again is harmless; the server never replaces a registered recovery key (SecureMessageTransportException.LastDeviceRecoveryKeyRejected with CONFLICT). Never called implicitly. Throws SecureMessageClientException.NotInitialized without an active key.