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've bolded the key sentence. It might cover a lot of ground.
If I declare an action
I kill the orc and then I succeed on my action (in some systems that might be winning an opposed check; in D&D that normally means making a successful to-hit roll and then making a good damage roll) then other players
can't declare as their action I talk to the orc because the fictional positioning won't let them (unless they change the fictional positioning in some way (eg in D&D that could be using a Speak with Dead spell).
In that sense any change to the ficiton ramifies down the line to future action declarations.
In some systems, social conflict resolutions which, in fictional terms, brining it about that someone is
persuaded or
cowed or
ensorcelled or the like create, in mechanical terms, hard constraints on action declaration similar to the orc being dead. This is how Duel of Wits works in Burning Wheel: if you lose, there are actions that are off the table for your character. It's also how I adjudicate Prince Valiant (the rules there are a bit more vague or incomlete than BW) as in the examples of play I posted about upthread. As farr as the actua process of play is concerned, the comparison to the dead orc is literal, not analogy or metaphor. I thik we all can see that, if player B declares
I talk to the orc after player A's PC has killed it, the correct response is
You can't - the orc's dead so in these systems. So, absolutely identically, in the systems I'm describing in this paragraph f the player delcares
I get ready to lead the charge after another character has won the social contest to extract agreement that he will lead the charge, the correct respoinse is
You can't -you agreed to let so-and-so lead the charge, remember?
That's not the only way of handling that sort of change in the fictional positioning. In some systems (I'm thinking some PbtA and also Cortex+ Heroic) the player might take penalties to checks that push against what the dominating character wants the PC to do. In Cortext + Heroic that sort of penalty functions (mechanically) just like injury or exhaustion - they all operate as buffs to the opposed check - and if it gets big enough then it takes the character out of play just like too much exhaustion would. In the exhaustion case the GM gets to narrate the PC collapsing for physical reasons; in the emotional or influence case the GM gets to narrate the PC collapsing from stress, or doing something else appropriate to the influence that has been exerted.
I've never played Fate, but I think the structure of compels is roughly comparable to this: if the player ignores the influence/constraint, s/he takes a mechanical penalty (in Fate, that takes the form of a resource expenditure).
Burning Wheel has another interesting mechanical framework in this general terrain: in BW each charcter has a Steel attribute, and if you fail a Steel chck you have to choose from one of four options to choose from: run screaming, swoon, fall prone and beg for mercy, or stand and drool. So the ficitonal positioning (
I failed my Steel check, so my character's courage has failedi) not only precludes action declarations that would contradict that fiction but correlats to a tight mechanical constraint on what happens next. Classic Traveller has morale rules that look like a bit like this, too: if you fail the check you have to declare your character either breaking or surrendering (at some tables maybe the GM decides this rather than the player, in which case see below).
Yet another mechanical possibility occurred in my BW game (BW is a very mechanically interesting, complex and flesible system): when a dark naga ensorcelled a PC, I had theplayer rewrite one of his PCs' Beliefs to recognise the new situation, which then - within the structure of that game - changes his incentives in playing the PC. The analogue in D&D 5e would be changing an Ideal or a Bond.
In D&D (all editions, I think) there can be mechanical effects on a character (PC or NPC) that allow control over that character's action declarations to be changed. Rolemaster also has those effects. I imagine so do other RPGs that are to a greater or lesser extent in the mould of D&D. I suspect there are some Classic Traveller tables that run morale like this too - ie that failing a morale check lets the GM dictate actions for the PCs whose morale has broken.
From the point of view of
burdens on play agency, what is significant about this last category of mechanical effect is not that
it lets someone else make things true in the fiction of your PC, but rather than
for the moment you can't declare actins for yur PC. It's like the PC being dead, or drugged, or utterly immobilised because bound and gagged.
EDIT: I just saw that this post is an appendix to posts that
@Campbell and
@Fenris-77 already made.