> I would say that both A and B would claim to be X and have the "continuous"[1] experience to be X while agreeing that they are distinct persons. I think that the question of whether A or B, both, or neither is the true X, is not a scientific question, and as a philosophical question, a fairly empty one.
I agree that it is not a scientific question, but as with virtually all ethical questions not being scientific doesn't mean it's empty. They are, in fact, very fundamental. This specific question might be empty now, but it won't be when people start messing up with brains (e.g. advancements in Neuralink).
In the hypothetical scenario, it is the most important question in the whole world from X's perspective because it involves, you know, them dying. X cannot be either of A or B, because they are indistinguishable (any argument proving A=X also holds for B=X, but A!=B so they are wrong). Saying that X is both A and B requires dualism (A's and B's experiences somehow get beamed to a third consciousness). Only X's death and A and B independence (with the same memories) is compatible with a position that doesn't involve contradictions or souls of some kind.
> Regarding the challenge, I would expect that the consciousness would be forked: there is a "me" that would awake inside the machine and would be very glad to be alive, while the "me" outside would experience dying. This seems to go against the exclusiveness of the experience of being themselves, but assuming the existence of the magically perfect duplication, both would be valid experiences and again neither could make a claim about being the real me. I don't find this to be a contradiction.
Do you not find a contradiction in saying that you cannot make the claim of being the real you just because your brain was copied? Suppose that this copy happens without you falling asleep and without you noticing: have you stopped being you?
> But all of these scenarios have been explored extensively. Are you familiar with the Egan's "Permutation City"?
I read it a while ago. From what I remember, it is based on Tegmark's mathematical universe hypothesis, which I find being hopelessly confused about the nature of reality. Doesn't the novel assume the consequent (it starts from the assumption that you can do this kind of manipulation with consciousness)? I had similar issues with Accelerando.
> [1] what does "continuous" even mean? Do one have a "continuous" experience of being yourself after a night's sleep? After anesthesia? After a coma?
Sleep and anesthesia? Of course: your brain is still active even if it is not recording memories. Coma it depends: unless you're brain dead, still yes.