I don't think that I'd say that a dice roll and the GM deciding are equally "outside of your control" as you suggest. With a dice roll, generally speaking, as a player I'm going to have some idea of my chances of success....certainly I'll know how good my character may be at a given task. For example, to kick in the door, my character has a high Strength and so it's reasonable he can do it. The GM will likely (hopefully) also share some details on the door that will help inform my decision. Ideally, he'd state what the DC of the check would be. And so on. So I can then as a player calculate my odds and the risk of failure, and can then proceed with the attempt or not. I'm making an informed decision.
These same details are also going to be shared with a player when the DM is going to make the full decision, though. The player can calculate the odds and and make an informed decision on whether the attempt has a good chance to auto succeed or auto fail. If making an informed decision gives agency to the player, then that agency is present when the player makes an informed decision to attempt something that he knows is very likely to be impossible, but is making the desperate attempt anyway and the DM says no.
If the GM decides, then I likely have a less clear idea of my chances. That may not be the case....I may still have a good idea of my chances because the GM has told me the door is made of flimsy wood and does no appear to be barred from the other side, and he's hopefully going to factor in my high Strength score and so on. If so, great. This is much more simple with certain actions than others, and the door kicking example is an easy one for sure.
Imagine a more complex action declaration, maybe of the sort offered in the OP.....a PC insulting a NPC. Now, we don't know exactly what the intent of the insult was in the OP, but let's imagine it had a purpose. Let's treat it as an intimidate check trying to convince the baron to negotiate with the PCs by letting them know if he doesn't, they're not fond of him and may act against him.
In such an example under the GM decides method, I may have no real sense for chance of success or consequence of failure or anything else. It's a much less informed decision. The GM can choose to narrate a result that I may not have thought was on the table.
If you're walking into a meeting with a despot that you know acts in this manner, "Going into the meeting,
they knew the ruler was unstable and severely punished any dissent in his land - having heard from various NPCs and seeing it firsthand.", you have the information to make an informed decision about whether or not you should make an attempt to dissent in his presence, and that the consequences will be severe. And, since you heard stories about what he has done from "various NPCs" who saw it first hand, you have an idea of what those consequences will be.
Earlier in the thread, many people said that the DM controls when the mechanics get invoked. The DM decides if a declared action is outright successful, or if a roll is needed to determine success, or if the action is outright impossible. This gives the DM all authority on when the dice are rolled. Yes, we would expect and hope that the DM would use this authority in good faith and with principles guiding him in some way. But these factors are going to vary much more than game mechanics, no?
I wouldn't think all that much. The rules are very clear that the DM calls for a roll when the outcome of an action is uncertain and has a meaningful outcome. The rest of the time the DM will say yes or no. And while the DM is empowered to ignore the rules, it would be in bad faith to do so in a manner that goes against the spirit of the rules. The DM should only go against the rules when there is a good reason to do so. When I do that, I explain my thinking to the players as I do it.
The players can reasonably rely on the DM only deciding when something will clearly succeed or clearly fail, even if the success or failure is due to something the players are unaware of, which occasionally happens.
If you're playing with the same group you have been for some time, you may have a very strong sense of how your DM may judge these things. And that's great. I'm lucky enough for that to be the case for me and my group. But even still, at times conflict still comes up. No one is going to be 100% consistent. And no two people are going to agree on what 100% consistent may mean.
Now, if you are playing with a group that is new to you.....you have far less past experience to guide you here, so it becomes even less clear. How can you say what your expectations should be under this system? It's a much bigger gray area.
So, although yes, shooting down every idea is bad faith play and I doubt such a DM would keep a game together, but it doesn't require bad faith play for there to be less player agency under such a system. The DM could be doing everything that he thinks is right, and another DM could also be doing everything he thinks is right, and you can have two different ways it plays out.
Less clear still equals a very good chance to read things correctly, though, so long as the DM is describing things the way he should be. If the DM is giving poor descriptions then there will be issues, but those issues will affect new and old players.
I don't really agree with your number 2, and therefore your conclusion 3. Doesn't that render the idea of player agency moot? When is there not player agency in such a broad application?
No it's not moot, and broad doesn't take away meaning. Think of how often you're near earth in your daily life. I'd wager for probably 99% or more of your life there is earth near you. That broad presence doesn't take away meaning from the word earth or what earth means. It just means that the vast majority of the time, earth is present.
It's the same with player agency. Since my PC is shaping the fiction with the vast majority of both his successful and his failed attempts, agency is present. I can make an informed decision and shape the fiction with my actions whether I succeed or not. And if we add "informed" into the mix of what grants agency, then even an answer of no from the DM will still result in agency, still the player made an informed decision, decided to make the desperate attempt, and through that attempt shaped the fiction into something new.
You can have greater and lesser amounts of agency depending on the system, but a DM acting in good faith results in agency almost without fail, regardless of system. I doubt there's a RPG system out there that is designed so that there is no player agency.
Also, the bit about players "having full control over how their character will shape the fiction through both successes and failure"; I don't think this exists in D&D, in many cases. The player doesn't decide that when he fails to kick down the door, he breaks his foot, or he makes such a ruckus that it attracts a wandering monster, or any other result of the failure. The DM decides that.
I disagree. First, the player isn't going to break his foot unless the player is playing in a game with critical fumbles, in which case he is making an informed decision to kick down the door knowing that if he rolls a 1, his foot could break. Second, even a brand new player should be able to realize that kicking a door is going to make a lot of noise and could be heard, success or failure. So he's making an informed decision to make a ton of noise, too, unless makes the informed decision to use a silence spell first and not make noise.
Are you saying that player agency is only taken away if control of a character is taken from them?
That or bad faith DMing where the DM says no inappropriately. Though I guess that could be viewed as a form of losing control of the character.
If so, does this apply to such in game effects as Charm and Dominate Person?
Sure, but an in fiction method of taking away player agency is perfectly acceptable. It's going to be limited in duration.