Correct. Since that has not been established, the player cannot unilaterally will it into existence. It might be the case that the GM frames a scene which reveals its position, generally as the result of a player move of some kind. Or it might be the case that the conversation that is play just naturally results in a slow accumulation of knowledge about where the ruby might be and where it definitely can't be until only one answer makes any sense. That's also a valid path, that doesn't specifically require anyone (GM or player) to declare anything specific. For example, one might overhear a guard saying that their employer doesn't trust the safes anymore, so they hid the ruby elsewhere. That doesn't establish where the ruby is, but it now conclusively establishes that no safe will contain the ruby, no matter where the PC(s) might look. Later, a bribed magician might say they helped furnish various magical means of storage to the possessor, which positively identifies that some kind of magical means were used to secret the ruby way. Finally, the player might hear the possessor curse at being unable to check on the ruby because their basement panic room is warded against planar travel--which, when combined with the other pieces of information, means that it must have been secreted away using Leomund's secret chest or something similar.
And all of this makes sense. However.....
In the total absence of establishing fiction, the player does not get to simply author whatever they like, whenever they like. That's against the rules. What is done must follow from the fiction, not simply invent fiction from whole cloth that happens to be convenient to the player. (At least in PbtA games. I can't speak to other systems, having not played them, but I'm certain they will have analogous requirements.)
....when I made this exact point (in different terms) in a long-ago thread I got shot down for it.
Yep. And as long as that information remains unknown to you, you do not have the ability to just fiat declare "It's here!"
Well, I have to then succeed on my roll. Failure, or even success-with-complication, means I haven't fiat-declared anything. But if memory serves, success is supposed to be sacrosanct and the GM can't deny or subvert it, correct? If yes, then in effect I
can fiat-declare it to be there by stating my intent is to steal the ruby and my action to do so is to pick the safe, and then full-succeeding on the roll.
I'm not saying this is a good thing. I'm just saying it's a likely effect of the rules as designed.
Nope! That's exactly where you've gone wrong, and where I've repeatedly said you've gone wrong, but you refuse to consider it.
Instead, it is: Task - pick the safe. Intent - steal what is inside.
But I'm not here to steal whatever's in the safe. I'm here to steal the ruby, and may or may not even care what else might be in there if anything.
But the ruby's position isn't quantum. It just isn't actually known right now.
In this case there's no difference. The GM doesn't have its location in her notes because she doesn't have notes, so she doesn't know where it is. The players obviously don't know where it is. Instead, it shows up wherever the dice decide it'll show up, and until then its location is a quantum thing - it could be anywhere.
It's the same as the quantum-Ogre problem, where the Ogre shows up no matter which way the PCs go but until then its actual location is unknown.
A "quantum" thing means it could genuinely be anywhere. An unknown thing simply means...we don't know enough to know where it is. We're going to have to discover where it is first, in order to find it! That's...kind of the point of finding it?
Which is fine in map-and-key play because at least then the GM knows where it is, and finding it becomes, in effect, a puzzle for the players to solve. But when the GM doesn't know where it is either, then there's no fixed solution to the puzzle which makes it...well, no longer a puzzle, in any case; the players keep searching in different reasonable spots and the dice eventually tell both the GM and the players where it is.
Otherwise, by your logic, every time you don't know where your keys are IRL, they are in fact in each and every possible place they could theoretically be, simply because you don't know where they are yet.
Nope. There's a fixed and pre-set solution to the puzzle of where my keys are, I just don't know what it is at the moment. But (assuming someone isn't playing tricks on me and moving them around) when I find them I can have full confidence that's where they've been all along.