The claim is not that the EDT agent doesn’t know the mechanism that fills in the gap (namely, Omega’s strategy for deciding whether to make the numbers coincide). The claim is that it doesn’t matter what mechanism fills the gap, because for any particular mechanism EDT’s answer would be the same. Thus, we can figure out what EDT does across the entire class of fully-formal decision problems consistent with this informal problem description without worrying about the gaps.
The claim is not that the EDT agent doesn’t know the mechanism that fills in the gap (namely, Omega’s strategy for deciding whether to make the numbers coincide). The claim is that it doesn’t matter what mechanism fills the gap, because for any particular mechanism EDT’s answer would be the same. Thus, we can figure out what EDT does across the entire class of fully-formal decision problems consistent with this informal problem description without worrying about the gaps.