What I mean is that for branches to affect each other, the branches must become completely not separated: every difference between the branches must be erased, including the ion and also the atoms in all the observers. This makes communication meaningless, because there's no longer anything the sender knows that the receiver doesn't also know.
Inter-branch communication while preserving separate branches shouldn't be possible under the standard many-worlds interpretation, because it violates linearity.
"Reality is amplitudes flowing between configurations" is helpful for understanding conceptually why MWI (and quantum mechanics generally) predicts this won't work. For branch 2 to influence branch 1, the two branches' amplitudes would have to flow to the same configurations. So suppose Alice#1 (with high probability) receives a message, and is still aware that she is #1 and didn't compute the mess...
The part where they remove the experimental scaffold is the only thing in this table that goes backwards from Opus 4.* to Mythos, right? (Lower is better for MSE.)
Some things did get worse from 4.5 to 4.6, which I agree is interesting.