The OP did mention that the party had met with other factions seeking to oust the Baron due to his capricious rule and that the party had refused to ally with them.I know I have seen the argument that it followed from established fiction. That's part of what the comments about foreshadowing to the players that he would treat any who insulted him harshly was meant to show that the outcome was proper due to established fiction. It's not an argument I fully buy into - but it was an argument made nonetheless.
@pemerton
I will respond more fully later. I have a question. Isn’t it true that in many games where players dictate fictional outcomes that they can dictate what other PC’s do via those outcomes? If so isn’t that taking away at least in part some players agency to declare their PCs actions?
I don't understand what you mean by "the dice determine the outcome". Can you give an example?
All the examples of RPG mechanics that I'm thinking of at the moment involve a player declaring an action for his/her PC and then using the dice to find out whether or not the action succeeds.
I'm asking how is that fiction authored? By whom? And how is that authored ficiton used in subsequent adjudicaitons of declared actions?
But now you're just assuming that players dont have agency. From time-to-time I GM games that take place in the "real world" - Cthulhu Dark and most recently Wuthering Heights. The players as much as me get to express views over what can be done in the real world. Eg in one of our Cthulhu Dark sessions the PCs had taken control of a tug boat and the player who knew the most about tug boats told us what could be done with it.
In my games set in non-real worlds - eg my 4e game - the players also help decide what can or can't be done. Eg in that game it was the player of the invoker/wizard who generally took the lead in deciding what was possible to be done with magical effects.
This is why - multiple times upthread now - I have emphasised that establishing constraints of genre and fictional positioning can be a matter of negotiation and consensus, in which the players exercise their agency as participants in that process. It need not be unilateral GM authority.
And the fact that it can be negotiated is a reason for distinguishing it from action resolution procedures which, in the traditional RPGs that I play, are not about negotiation but rather involve rolling dice to see whether or not the fiction unfolds as the player is hoping for his/her PC.
[T]he definition of player agency that you posit here is uninteresting because in every RPG players have it. It's not something that varies.
Given that, in a traditional RPG, the way a player changes the shared fiction is by declaring actions for his/her PC and then having those resolve, the connection between player agency and action resolution procedures is not coincidental.
If a player can't change the shared fiction; if all s/he can do is prompt the GM to make such changes by describing what it is that his/her PC tries to do; then what is the role of the player in the game?
@prabe
I do not understand what you mean by having agency negated. Agency is not something you either have or do not have. You have a certain amount of agency over a particular thing.
When I say something like "Something being impossible doesn't negate player agency?" It doesn't reduce it, it doesn't mean you don't have it. Just because something is impossible doesn't mean the player doesn't have agency; it doesn't mean the player has less agency.
I hope that's clear.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.