1. One single future is chosen at every turn and we go down that rabbit hole and never turn back. The author's determinisms all land into here.
2. Explicitly modeled nondeterminism, whereby we execute all the future possibilities (e.g. nondeterministic finite automaton NFA, Mac Carthy's "amb" operator.)
I can't give you a star sticker if you don't mention these, sorry.
> None of that mattered at the scope we were modeling, so we abstracted it all away: "on receiving message, nondeterministically enter state A, B, or C."
That sounds like the author is describing an NFA.
> whereby we execute all the future possibilities... e.g. "amb" operator
Isn't "execute all possibilities" closer to the dual of amb than it is to amb? At least in terms of how the denotation of amb is operationalized.
But it is a good point that sometimes you want to give an actual operational meaning to a literal non-determinism operator.