> Just trying to think about how you can Guarantee that neither the manufacturer or yourself knows the private key
What for? I see footguns in this scheme, but I don't quite see the benefits.
In general, I think that both cosigners and blind signers are unlikely to make much much sense in multisig setups - much more useful in miniscript wallets, where you can do more 'experimental' stuff with the primary spending path, while keeping recovery paths straightforward.
