In the third situation, the GM has decided that something unlikely will happen.
<snip>
In the first situation, the PCs are treated just like any NPCs in the situation.
In the third situation the PCs and NPCs are also treated the same, in the sense that they see the same things, have the same ingame opportunity to stop the fleeing wagon-driver, impede the guards, etc.
The third case is the clear outlier here. That's the situation which is more of a railroad than the other two.
How is it a railroad? What player choice has been blocked/negated?
Yes, the second situation is a product of (indirect) player agency. Anything that happens after that is an extension of player agency.
In the third situation, anything that happens is a direct result of the GM's imposition of the unlikely scenario.
I don't really follow this. In the the second situation, the context within which the players can declare actions for their PCs depends upon the GM's direct imposition of a timeline. In the third situation, the context within which the players can declare actions depends upon the GM's direct imposition of the overturned cart.
And in either case, anything that happens is a result of the players' engagement with the GM's "imposed" fiction.
If an average of 5% of each day at the Garden Gate is spent with an overturned wagon full of weapons, but you've contrived that 100% of the time that the party arrives at the gate involves this happening, then this encounter is not reflective of the reality of the world.
As I described it, this is the first time the PCs arrive at the gate. That is an event that happens once. So, in the third scenario 100% of the first arrivals of the PCs at the gate (ie all one of those events!) involve an unlikely thing occurring.
I would say that a GM preference for interesting, if it biases the occurrence of events in the game, is a form of railroading.
In that case, why is a GM preference for pedestrian events, which biases the occurrence of such events in the game, not equally a form of railroading? They are both instances of GM decisions about content introduction.
Whenever the DM decides that something unlikely happens, it feels hollow and contrived.
The GM also decided the timeline. And the GM also wrote the setting description. (In the first two GM-prep scenarios of the three that I outlined.) That was part of the point of my post - in all three scenarios the GM is making decisions as to what happens in the fiction.
The situation where a PC encounters a powerful demon eating a corpse is entirely something that could happen in a game I run.
How? Can you describe how such a scene might occur in your game?
The naturalistic GM decides that the events which happen will be the events that would otherwise occur if the world was a real place, conforming to known details of that world (not subject to narrative causality). Imagine what's going on in the world, on a typical day. Like every other aspect of being a good GM, some people are better than others at this. Practice helps.
An easy tip for making the world feel more realistic (less story-y) is to avoid all unlikely events.
Once again we return to the Spartan world. For me, a Spartan world is not remotely realistic or verisimilitudinous. Every day things occur to me that are not more than 5% likely to occur on a given day!
On a typical day, the rebels
could have their wagon overturn and their weapons hence be discovered. Such events really do happen in the world. A world in which nothing like that ever happens seems, to me, a robotic one, not one I woud want to roleplay in.
(Furthermore, how often do wars occur in fantasy RPGs compare to their prevalence in the everyday life of the campaign world? Or invasions by demons, zombies or dragons?)
What's the difference between the DM rolling a d20 to hit you, or just deciding that a 17 will be more interesting?
This was answered upthread by [MENTION=75791]TheFindus[/MENTION]. One is action resolution, the other content introduction. They are different elements of game play.
When the GM writes a timeline or draws a dungeon map or writes a setting cosmology, this is also content introduction, and it is not done by rolling d20s and damage dice.
In terms of player agency, though, an RPG is a lot like real life - your only agency is what you can causally affect within the world
I don't follow. When I play an RPG my agency consists mostly in choosing to say one thing rather than another to the other people at the table.
You seem to be talking about the imaginary agency of some imaginary people (the PCs). When I talk about
player agency I am talking about the actual agency of some really existing people - the players of an RPG.