I think this more effectively explain the issue with your reasoning:
I got a similar vibe from
@Campbell 's exelent post a while back.
The resolution lie in that in this style of play your wishes as a player should be surpresed compared to the motivations of the character. This is similar to how some sim play is requiering the self dicipline of not to take meta knowledge into account when declaring actions.
If it is a common understanding of this, then the player agency you refer to evaporates. It is true that there is a mechanism for modifying the world outside standard in-fiction causality, but this mechanism is still based on
character, not
player. There are hence no player agency competing with character agency in this type of play as long as you
are not a weasel