Hanson writes: "This paper thereby shows that agents who agree enough about the origins of their priors must have the same prior."

Isn't this really the same as saying: agents that have the same priors (= theories about the origins of their "priors") ought to reach the same conclusions given the same information - just as per Aumann's agreement theorem?

You're saying P ⇒ Q, Robin is saying weaker-version-of-Q ⇒ P. I think.