It is a whole lot more organic than that.
Think of the GM’s Turn and the Player’s Turn as rhythms.
Let’s use some Gygaxian rhythms as examples, since you invoked His name.
The GM puts a hallway pit trip in the player’s way and they have to use their skills to navigate around it and then they have to fight the orcs.
From the book, page 70:
“The GM will point to certain tests to overcome
obstacles. The players may suggest other tests,
other ways to navigate the situation.”
After those two conflicts are resolved (and just because two rolls are what starts resolving them, that doesn’t mean all will be finished in two simple rolls), we can take it to the Player’s Turn. But, odds are, it won’t be two simple rolls. Odds are there will be some twists, making things more complicated.
Once the two conflicts the GM decided when she made the mission up are done, we cut to the Player’s Turn.
In Gygaxian terms, this could be the players sealing off the door to a secure room with iron spikes and resting up in order to heal wounds or get their spells back.
But let’s see this in Mouse Guard terms.
I ran a game and the two conflicts were a late spring snowstorm and a beaver who had built a dam that flooded Sprucetuck and it was ripping up pieces of the tree town in order to take back to its dam.
There is structure but structure doesn’t mean railroad. It doesn’t mean the players don’t have choices. You know what the two conflicts are going to be but what you don’t know is how exactly the players will solve them or who their attempts to solve them will further complicate matters.
The beginning is set (Gygaxian: there is a dungeon with treasure, get to it) but the end is undetermined and that is why there are no rails. In a railroaded adventure, the end-point is known and their choices are not meaningful.
Guardsmice have meaningful decisions to make.
Hope that helps.