With gmail, both attachments showed just (constant-width) single-line names of the attachments, "junk.txt" and "junk.diff" (without the quotes).

On Thu, Jun 28, 2018 at 6:19 PM, Doug McIlroy <doug@cs.dartmouth.edu> wrote:

This tests a guess about anomalous behavior of the
mailing-list digest. I apologize for inflicting it
on everybody.

Doug