Just to say that while I haven't found a way out of the gdb EOF trap, I
have found an alternative test approach.
rather than use cat-file --batch-check, I've drilled down the repo
https://gitlab.com/ricardo.qtec/bug-gitwin.git via log, cat-file -p
HEAD^1, ls-tree and cat-file-s to get to the bigfile and its size. So
I'm now starting debugging why that (cat-file -s 41ba8fda505291b7) gets
the wrong answer - it is a command I can easily execute in gdb and try
my hand at old style debugging (it's been >30 years!).
I'd still be interested in an answer to doing an EOF on mintty they gets
through to gdb...