The types of acts to be performed are discussed with the agent BEFORE the shoot, and that is how the amount of money paid to the performer is determined. The agent knows BEFOREHAND the situation,(no comdoms,no blood borne pathogen protection) the perfomer is to work under. Once an agent sends a performer to a shoot that he knows is illegal, the performer will have no problem having any "contract" with that agent voided. It is common knowledge that you cannot 'agree' to violate the law.
It is the agent who negotioates with the producer/director on behalf of his client(performer). The agent knows what the situation will be. Or the agent could lie and say he didnt know what was going on, in which case, he aint much of an agent.

A vast majority of porn performer/porn agent "contracts' are not worth the paper they are prited on.