Raven's purge says "Zytera has a contract signed in Krasylla's blood hidden in Zygofer's clothing. The contract prevents Krasylla from harming Zytera." and "In the partially decomposed cloak worn by the old man, Zygofer, is the parchment that holds the contract that binds Krasylla to Zytera".
"Partially decomposed" says to me "random passersby can see the contract and think about stealing it" / "it might fall out accidentally", which don't seem right to me.
But what if the contract was made out in Maha signs (which we know are a language of magic), as part of tattoos on Zygofer's body? (Where the ink of the "I agree" sign is Krasylla's blood.)
That makes the agreement unstealable.
It also explains why Krasylla is trying to become something else: as well as being far more powerful, it will arguably no longer be Krasylla, and therefore not bound.