I think the problem you had is basically that's in uncommon to be distributing bare public keys in the most common cryptography contexts. Public keys are nearly

I think the problem you had is basically that's in uncommon to be distributing bare public keys in the most common cryptography contexts. Public keys are nearly always part of certificates. I looked at the @bluesky identity post, and it seems to me that what's being described in the granting process is very close to a self-signed certificate. To link two identities, couldn't you create a self-signed certificate with two SANs that identify your identity on P1 and P2 and post the same certificate to both of them, then send links to the two posts to the ledger? An X.509 certificate is already a structured method to create a payload consisting of a public key, various claims as to identity of the subject, and a wrapping signature.