According to `git blame`, this was introduced June 2023, i.e. after your audit in 2019. But maybe it was moved from an older piece of the codebase, I didn't dig too deep.
(Looks like the IncludeSec folks did a decent job in 2019. Hi Eric!)
(Looks like the IncludeSec folks did a decent job in 2019. Hi Eric!)
However, I misread this: I thought the padding was being done on the cleartext signing side, but this is padding of the signature itself. So there's some malleability here, but it isn't susceptible to DO'1985. I'll update my top-level comment.