And yes, now that we have UAVs, we'll probably have to revisit the
question of whether shooting down an aircraft automatically constitutes
an act of war.

Like U-2s and other recce planes, or the several civilian airliners
that the USSR, US and Israel (there may have been others, I don't
remember) shot down.

Going back upthread, I think the essential question is, "What do you
want to do about it?"