I asked the question originally because:

• it should be easier to analyze a now static configuration laid bare before you, like a video you can wind back and forth as desired, than predict something that hasn't occurred yet.

• there should be a way to detect agency in retrospect, otherwise it's no agency at all. For simplicity (an extremely underrated virtue on this forum) let's take an agent which does not care about evading detection.

Re your conditions 1 and 2, feel free to presuppose anything which makes the problem simpler, without cheating. By cheating I mean relying on human signs of agency, like known artifacts of humanity, such as spears or cars.