FEATURE REQUEST: Crypto-request for descriptors

[ChristopherA]

Looking forward at the whole cycle of what happens between a transaction coordinator and 3 signers, there is one last phase where the transaction coordinator, having all the xpubs, ought to have the option send the final descriptor to all the signers (if they want it).

Not sure if this should be a 1.5 thing or something we'll learn when doing the transaction coordinator. Some signers have no state (Passport) and will not want it. Others, like Gordian Seed Tool, may need it so that it can create a backup accounts associated with seeds, or initiate a policy where it won't sign any PSBTs for accounts that it didn't get registered.

I see the possible 1.5 feature just simply allowing basic crypto-request export and import of a descriptor, then puzzle out how/when it might work more fully in a flow in a subsequent releases after we learn from the transaction coordinator.

Definitely a stretch goal.

[ChristopherA]

The more I think about it, it is more complex than I originally thought.

Basically, a signer that wants the final multisig descriptor back (like Gordian Seed Signer should, but stateless wallets like Passport will not), when it returns a successful crypto-response of crypto-hdkey, it should embed in it crypto-request to "please send descriptor back when it is completed by all the other signers".

I don't think we can put a crypto-request inside a crypto-response, so that makes this immediately not possible in 1.5, and thus backlog.