The soldier's name is Dooryard. He is an active Corporal in the Mingxian Army. The communication was, “In position.” The Librarian is doing some diplomatic visits around the city before the festival. She is a very massive creature, so she has been traveling quietly in the night time to avoid much attention. The Librarian wished to go to a new library, so Dooryard is assisting the location change.
It appears that someone else might have an issue with the Moon Guard being here. It is doubtful that a standard assassin can even put a scratch on The Librarian in the first place, but there's no reason to allow trouble just because it might amount to nothing. It is fairly odd that someone would attack now, before the Emperor even arrives. It will just increase security when the leader arrives.
While Dooryard is of the belief that whoever is conducting this attack has poor planning, it does not detract from his duty.