There is emerging in this thread, and I have seen it emerge in many previous threads, an implicit assumption that there are four basic ways to produce the fiction of RPGing:
(1) GM authorship in advance;
(2) GM unilateral (or close to unilateral) authorship in the moment of play, which is like an ad-libbed version of (1);
(3) Player authorship in advance;
(4) Player authorship in the moment of play which requires stepping out of the character because it is very similar to (2) and hence to (1).
The great insight which RPGs like Apocalypse World and Burning Wheel try to systematise is that this list is in fact not exhaustive. There are at least two other possibilities:
(5) GM authorship in the moment of play based on constraints that emerge (significantly, probably not exclusively) from the player's play of his/her PC;
(6) Player authorship in the moment of play that does not require stepping out of character because it is part and parcel of action declaration for the player's PC.
AW, DW and (to the best of my knowledge) many other PbtA games make extensive use of (5).
BW makes extensive use of (6) and uses (5) when it comes both to scene-framing and the narration of consequences of failed checks.