(1) is contentious, given that in many cases - as @hawkeyefan was pointing out upthread - a canonical account of what a person does includes an account of what happened, which includes or entails an outcome.1) they decide what they do, but not the outcome
2) there are plenty of cases where their action is not just negated, then they do affect the shared fiction
But even if that contention is set aside, getting to describe that I put out word, via my herald, that I would like an audience with <such-and-such a local noble house> in a context where the GM decides what actually happens, is low agency. It's the lowest degree of agency a player can exercise and still be playing the game at all.
As for (2), if the GM is always at liberty to negate/veto, then the player is really just making suggestions that the GM can choose to take up or not. I regard that as low agency. Taken literally, the player isn't playing the game at all, just making suggestions to the GM who is playing solo.