UX Issues in Export PSBT via System Share Sheet

[ChristopherA]

When I export a PSBT as a file and then via System Share to iCloud Files, I get a very confusing dialogue (see below)

• I can't seem to pick the name of the PSBT to save, so saving then asks if I want to overwrite or Keep Both. I can only really use the Keep Both option and puzzle through later which one is which.
• The default name is GordianSigner.psbt. Besides that we now call this GordianCosigner (maybe a global search in the code is still need), this is insufficient. I suggest maybe we use a PSBT fingerprint based on the LifeHash used in GS for PSBTs now.
• I'd like to know what else is already in the folder (in this case the Gordian folder already has some files, but in this dialogue none are shown even though there are some already there. I don't know if it should only show .PSBTs or all files.

Related:

a) Other apps default to folder to make things easier, should we? Gordian, or maybe Gordian/PSBTs? b) Is there yet a standard way to add comments to PSBTs? I'd love to offer some metadata about this PSBT. c) I think it would be fabulous if we could add the PSBT LifeHash as an file icon for this file. /cc @wolfmcnally is there an easy way to do this in UIKit? d) We need a generic UR for for hash that LifeHash uses, for those situations where the we want to share a LifeHash but not the source data, for those cases where the source data is on another device /cc @wolfmcnally

[wolfmcnally]

@ChristopherA d) We need a generic UR for for hash that LifeHash uses, for those situations where the we want to share a LifeHash but not the source data, for those cases where the source data is on another device.

The basic digest (we're calling it "the digest" now, not "fingerprint" to avoid confusion with, e.g., HDKey fingerprints) that LifeHash uses is the SHA256 of the data. As far as I can determine, there isn't an existing tag for anything like this, so we can define a CBOR tag and UR type that represents a SHA256 digest suitable for use with LifeHash. I'll create a BCR for this.