Hmmm I’ve been thinking about this problem of the blind signer as I have been vibe coding this:

GitHub

GitHub - kiwihodl/Seed-E: A neutral, non-custodial directory for third-party Bitcoin signing services, designed to be integrated directly into wallets.

A neutral, non-custodial directory for third-party Bitcoin signing services, designed to be integrated directly into wallets. - kiwihodl/Seed-E

And once I figure out the right approach I’ll build it in flutter + rust. I don’t think “traditional” multisig should be used, because of the poor key management should a key get compromised.. but it seems blind schnoor signatures and BIP32 seeds with blinded xpubs are the best option. Regarding the blind signers validation, can you take the presumption that their key / work should not need any proof other than it’s an empty PSBT from the person who bought the service? So that this person can request a signature, whether in the seed-e (lol, will change name) or the frost snap wallet and this is all the proof needed? By being blinded you’re kind of treated like a hot key in terms of just signing, but have metal backup of keys share / seed.. I’m not sure the best solution here, I’m early into just throwing things at the wall to see what sticks.