There is something I'm still missing.
The signature block at the bottom of the PGP/MIME signed message has
a signature type byte in it, text vs binary. Is it your assumption
that the value in this type byte should control the hashing of the
textual data which is earlier in the message?
I don't know if this has to be true, but it may be helpful for
implementations if it is true.
In that case there are two possibilities. One is to mandate the value
in this type byte, and thereby mandate the hashing which is done in the
message. Receivers would hash the message data according to the spec,
and then when they came to the type byte, they could either ignore it
or check it and complain if it is the wrong value.
The second possibility is to allow either value in this type byte, and
thereby require that the receiver read the signature before it goes back
and hashes the data (or else hash the data both ways).
Are these the alternatives as you see them?
Hal