Delegated authority is the right to act on behalf of another party within limits that are stated in advance. It is the oldest idea in organisational design, and it is exactly the question an AI agent raises.
Whenever an agent acts, something is answering the question of whose authority it is using. There are only two honest answers. An agent filling a role acts on that role's authority: bounded by the role's accountabilities and domains, and changed by changing the role. An agent assisting a person acts on that person's authority: bounded by exactly what that person can already do, and never more.
Keeping these exclusive matters. If an agent could both hold a role and assist someone, authority could be chained until nobody could say where it came from. For the same reason an agent assists only people, never another agent.
Where an action is consequential, delegation can stop short of the act itself: the agent pauses and asks a person who holds the authority, and proceeds only on an answer.