I have been struggling trying think of what in damnation that dagger could be, and I think my brain just leapt to a valid possibility.  Tanavast created the Honorblade for the Heralds with the specific purpose of granting Surgebinding.  Rayse created a blade of his own. Instead of granting an ability, it's intended to end the Oathpact.  Edit: and the gem in the pommel is a sapphire. To match Jezrien. Ten blades for ten Heralds?