When you say agency, just because this has come up in this thread and we are debating without getting back to how it ties to what you want, do you mean it in terms of the players being able to make meaningful choices within a setting and adventure you are running, or do you extend that to include stuff like what some of the others are talking about, like giving them power to control the narrative itself (i.e. is this agency through their character, or is this agency the player can exert on the world itself).
I don't know if you appreciate how loaded this in, in terms of building in assumptions about approach to play, and allocations of authority in play, that are very specific.
For instance, I have talked about action declarations like
I keep my eyes open for Rufus as we enter the borders of Auxol and
I believe that Evard's tower is around here somewhere - I look out for it. But I absolutely reject any description of them as
agency the player can exert on the world itself which is in some way different from
the players being able to make meaningful choices within a setting through their characters.
I keep my eyes open for Rufus as we enter the borders of Auxol is something that my character does, within the setting, that is meaningful. It's true that whether or not Thrugon meet Rufus depends, in part, on something that Rufus does. But that is just the same - if you ask me - as the case where
I attack the Orc with my mace. Whether or not I hit the Orc depends, in part, on something that the Orc does (eg dodge, or block and turn aside the blow with its shield).
I believe that Evard's tower is around here somewhere - I look out for it also declares something that my character does, within the setting, that is meaningful. It's true that whether or not Aramina's recollection is correct depends, in part, on something that Evard once did - ie build a tower. But again, most other action declarations also depend, for their success, on things done or not done by other persons and forces in the gameworld.
For reasons that are somewhat opaque to me, you and other posters might want to treat the action declaration about
meeting someone differently from the action declaration about
finding a remembered building from the action declaration about
hitting an Orc with a mace. I don't see them as different in any underlying structure or significance, and certainly don't think that the language you have used to try and characterise them is apt.
Here's an example of something that I
would accept counts as a player
exerting agency on the gameworld itself without making a choice through his/her character: the player declares
The King of Keoland meets an envoy from the Queen of Celene (and the player is neither the king nor the envoy nor the Queen nor otherwise connected to this event taking place). That's not an action declaration for a PC.
But no one in this thread has connected that sort of thing to player agency in the context of RPGing.