Corvina does not pretend the clause is a surprise. She has a copy of it in the desk, folded to the right paragraph.

CorvinaThe room is kept because the alternative is that it is not kept, and the last school that stopped keeping it lost the entire east wing to a fire that had no fuel.

CorvinaIt wants a keeper who knows what it is and a witness who will say what happened. Two names on the door, one light, sunrise.

Mione has been the keeper since she read the sentence. That is how these things work; the reading is the appointment.