I may have solved this. More reading, specifically on Debian’s site concerning manually adding (thanks Tom) a new boot entry (adding details for anyone else needing this) with:
efibootmgr -c -d /dev/sda -p 1 -w -L debian -l ‘\EFI\debian\grubx64.efi’
then I deleted the old Windows boot entry (still don’t know how it got there) with:
efibootmgr -B -b 0000
Any advice for automatically detecting the EFI partition path in the post.download scripts so I can dynamically set EFI entries after imaging? Querying the list and cleaning it up automatically is straight forward.
With all this, I’m a little lost as to how I’d image a drive and move it to another computer without considerable expertise. The original plan was to image drives, ship them to remote sites and have someone less-technical swap them out. Is this even possible? I suppose we could run efibootmgr remotely before swapping out the drives. Sorry, thinking out loud.
Thank you both for the pointers.