Carl's standing ban on children fighting, resented by the changeling kids and broken twice this chapter.
Carl issued a blanket "No child soldier" pronouncement that the younger changelings bitterly resent, especially since someone pointed out that Donut is younger than most of them. Mordecai tried to defuse the complaints with The War Movies and only made it worse.
Under the same rule, Bonnie and Skarn were explicitly banned from manning the door guns on Party Planner, especially on the day Operation Ruin launches. They stow away anyway; Carl catches them and orders Louis to land, but Open Hostilities begins first and Bonnie ends up saving the ship.
Carl's moral line on who may fight, repeatedly tested by the children under his command.