The arrangement whose requirements must be met before Donut is allowed to leave the ninth floor.
The Sepsis Whore deal sets conditions that must all be satisfied before Princess Donut is permitted to leave the ninth floor. Per Team Retribution's arrangement with Huanxin Jinx, if Katia eats the Orchid of Eileithyia's Grace and is whisked away to The Twelfth Floor as a celestial attendant, all the requirements of the deal will be met and Donut can descend.
If the alien doesn't honor the arrangement, Katia is either made pregnant and kicked out of the dungeon or has her constitution massively enhanced. The third possibility Carl refuses to think about is more insidious still: only one of Donut or Katia would ever be able to take the stairs, and neither could while the other lived.
The binding condition on Donut's descent from the ninth floor.