Agency (n.) is as good as useless as a conceptual apparatus on account of the fact that there are too many people doing different things or so many different reasons.
Agency (n.) is not the cause, but the effect, of failures at prediction. If something happens that was not predicted, one explanation is that the system in question my have agency, free will, creativity, and such.
Agency (n.) is represented in things the smaller and the less durable they are.
Agency (n.) is the capacity to surprise its observer.
Agency (n.) is to be found in systems rather than in individuals. It is the system's capacity to surprise its observer or to fail in prediction. Agency is not a cause, but an effect.
Agency (n.) is what is left when structure has done all it can do.