>> Actually, the problem with making ‘assert-valid-signature’ public is
>> that it raises &nar error conditions.

I’ve looked through the code; now I need even more information.  Please
elaborate.

>> It could be changed to raise a more generic &signature-error, but then
>> ‘restore-file-set’ would have to guard against it to re-throw it along
>> with a &nar-error (making a compound condition.)  And then ui.scm would
>> figure it out.  Blech.

Why would it need a more generic error?  Why would ‘restore-file-set’
have to rethrow it along with an &nar-error?  How’s ‘ui.scm’ relevant?
It’d be great if you could paste the code you were talking about.