I don't really see how this matters.
Upthread, multiple posters - including you, I think, but maybe I'm wrong one that - described the player as
deciding what the runes say. My point is that he didn't. He rolled dice, and won the roll. Much as a person might enter a lottery, and win: that doesn't mean they decided.
Much as a person might choose to have their PC fight in D&D, and win: that doesn't mean that they decided.
If you now want to ask
how does someone set stakes in MHRP, I'm happy to have that conversation.
How does the character know they have a chance of hitting it? I mean, if attack Bruce Lee I have no chance of hitting him.
They know that it
could be a map. Just as they know that an Orc is the sort of being that
can be hit.
Trying to parse out the difference in resolution by reference to these sorts of counterfactuals and statements of possibility won't work. This is because;
(1) The epistemic possibilities are the same in both; and,
(2) There are no metaphysical impossibilities at work: by which I mean that, in the real world if the runes say <X> then I can't read them to learn <Y>, whereas in fiction - as I posted upthread - metaphysics follow belief, it doesn't constrain true belief.
(That is why posters who say that the player
changed the fiction are wrong. There was no
established fact about the strange runes, beyond them being strange runes on the dungeon wall, until after the declared action was resolved. Nothing was
changed.)
There are two differences, not unrelated:
*Who gets to exercise authorial control over which bits of the fiction? Eg does the GM have sole authority over backstory?
*Must causal processes in the fiction and causal processes at the table be tightly correlated, at least where players are concerned? Eg if a player at the table does a thing that causes everyone to agree that <X> is part of the fiction, must that correlate to that player's character in the fiction bringing about <X>.
All RPGing that I know of allows some player authorship of backstory that violates the second dot point: eg the player deciding who and what their PC is; the player deciding facts about their PC's family, memories, etc. But often this is low-stakes stuff. Whereas the example of the runes is something that is less low-stakes.