A discrete process of intentional actualization oriented towards a distinct Telos.
I’m using the term Process broadly in the Whitehead-ian sense of a procession of occasions of experience. It’s here I acknowledge Process Ontology as a necessary logical prior to my working definition of “Agent” that you may-or-may-not share.
It suspect requires the capacity to experience and select, but not necessarily cognition. A sunflower and experience the direction of the sun, and selectively orient itself towards it - in that sense I’d describe the sunflower as definitively demonstrating agency while its capacity for cognition remains metaphysically ambiguous.
This category can (obviously) include biological agents such as animals and plants; however, this umbrella also covers what can be described as Sociocybernetic agents (such as states, corporations, religious organizations), as well as metaphysical agents such as spirits, deities, and Archetypes (which affect change in the world regardless of assumed ontological validity).