In these escalation scenarios either both sides commit to non-escalation or it doesn't matter. I don't know if current US policy had a nuclear retaliation for a strike against a carrier group, but it is such a high probability that any adversary likely considers is as true.

China or whomever attacking a carrier to destroy it with anything other than 1945 style surface warfare tactics leads to nuclear war, even if it's not the final decision point. The response to such an attack leads to nuclear war in enough projections.