If they starve North Korea the outcome will be the same as any action we take with the exception of giving aid.
We’ll push Kim into a corner and instead of facing a coup he’ll order the artillery fired, millions in Seoul die, possible nuclear detonation in Seoul or Tokyo, and we’ll flatten North Korea.
That’s the only possible outcome whether we strike first or they do.
It's better that they make the first aggressive movements so we can finally move on without this puppet-state occasionally annoying us. Sooner or later they WILL fire a nuke, and China will play innocent.