The treaty is for "The following terms are intended to govern the cessation of the recent hostilities between Ashtan, Shallam, and the Church." So, this says nothing about Tylin or any specific person. As Mistral said, Tylin has not have the power to declare war for the city. And he himself is not a city described within the treaty. It was not held about him. This treaty is held for the governments of each city, and the prelates of the Church. No convocation shall be used in hostilities with Ashtan. Just as if this were all about a Druid attacking, we could use convocation as this treaty does not cover Druids. To claim that what is said in the treaty encompasses ALL things would not be correct. Again, this is for the "recent hostilities between Ashtan, Shallam, and the Church."

Rezzo
sorry to bring the Druids in like that, but you all are the most obvious choice!

Penned by my hand on the 16th of Lupar, in the year 236 AF.