derives

the commands the handler returns. Without it, the handler's return type names them (CommandRequest<X>, an Iterable, a Sequence or a Flow of them, the subclasses of a sealed X); a handler whose return type names none (CommandRequest<*>, CommandRequest<Any>) must declare them here, or it does not compile. A wait chain may follow the saga's hop only into the contexts of these commands. A handler that returns Unit derives none and declares none.