Conversation

I think it's fine to use a different type. What I wanted to point out is that context property is for grouping related objects, and that there is another property that does exactly you want - relationship.

we're modeling a one-way relationship, not two way.

In a two-way relationship, there is an expectation that another Relationship object exists representing a reverse claim.

Is there another way around this issue that DOESN'T require Object Integrity Proofs?

I am not sure if integrity proofs really solve this problem... It's hard to tell without knowing who signs what (I didn't find that information in the FEP).