Interaction multiplexing

No, not in any foolproof way. You cannot infer presence. But you can do heuristics that are better than defaulting to whatever it was when you started this program by answering questions like which interaction endpoints are currently attached and responsive, and which of those have most recently had user activity.

tmux, for example, does not know if the local desktop seat is unlocked, but it does know whether there is a client attached over SSH that has recently been active.

So, sure, perfect correctness is probably impossible, but that just bounds the abstraction to something that is less likely to be completely wrong.