I think that one of Baker's points is that the structure of GM-controlled character vs player-controlled character combat looks like this, in a lot of RPGs.The advocate for the orcs might like to just say that the wall is gone. Poof, dispelled. But someone else at the table doesn't want that. This looks a lot like what I think folk have in mind when they use words like "negotiate". The player isn't willing to just consent to their Wall being gone. They challenge that. The group have agreed to let mechanics and dice settle such disputes.
And another of his points is that this is precisely where we see rules "easing and constraining" how the process of settling on a shared imagination unfolds.