Assume there are three players, Alice, Bob, and Chris. The turn order is Alice, then Bob, then Chris, with it currently being Alice's turn.
Alice has a loop that can infinitely create creatures, two creatures on the field, and 20 life.
Alice proposes a shortcut to do her loop a hundred times. Bob wants there to be at least 20 creatures on Alice's board (but wants to minimize this number to minimize how much life gain Chris's Soul Warden gains him), so he proposes to stop at only eighteen loops. If Chris weren't in the game, Alice would be required to accept this new loop (despite the fact that she just got information about Bob's plan). However, Chris and Alice both want Alice to stay alive (at least for now), so Chris proposes only seventeen loops (after which he uses Soul Warden to crew Aethersphere Harvester). Crewing the vehicle does nothing to stop Alice from resuming her combo, but both players just got information about Bob's hand, which causes her to not put another creature on the field.
Is this legal, or does Chris have to provide some kind of 'legitimate response' to interact with Alice's loop, other than the fact that Bob gave away information by proposing a stop to the loop?
Edit: Or is my understanding of the order in which players propose shortcuts wrong?