> No, we can't remove wrap_codec_error, as it is still needed in order
> to cover direct use of the codec machinery and to handle non-text
> codecs registered by third parties (the tests cover both these cases)

I searched on the WWW for third party codecs, I only found Unicode encodings (str => bytes).

I don't think that we need all these tricks to provide more informations on transform codecs and transform codecs are not used.