Is there a way to detect if an agent Z is listening to (and acting on) messages from Y? I can observe the messages that Y sends and the actions that Z takes, but I know Z is also listening (and acting on) other messages that I do not observe. I do not need to know how Z takes its actions, just that if sometimes it listens and acts on the messages received from Y or not.
For example say that Y can send either a 1 or a 0. Z can do one of four things say a,b,c,d. I can observe, the messages sent by Y and the actions taken by Z. But I have no information about what else is being sent to Z which effects the action of Z.
To my mind this has some similarities to steganography detection. Is Y sending messages with hidden instructions to Z? Zs actions are a function of the messages and other unknown factors.