At the moment, a correctly implemented avatar cache has to be keyed by the triple (our account, their identifier, avatar token).

It would be vastly easier to implement an avatar cache if we changed the specification for the avatar token to require it to be globally unique, so it could just be keyed by avatar tokens.

For protocols where an avatar is identified by (our identifier, their identifier, a timestamp), the CM could construct a token by concatenating those three things and hashing them or something.

We need to verify that Butterfly's implementation of avatars will still be spec-compliant after this. Haze and Gabble use the hash of the avatar, so their tokens are already globally unique.