UndeclaredSendException
class UndeclaredSendException(val subscription: String, val command: Class<*>, val member: String) : IllegalStateException
A saga's handler subscription sent command, a command of a class its @Sends([member]) does not declare: a bug in the saga, not an outcome of the command, which no retry changes. The handling fails unrecoverable, so the aggregate parks at once, and the command is not sent.