Comment by tom_mellior

I don't think it's a lattice per se, but Darcs had a notion of an "algebra of patches": http://darcs.net/Theory/GaneshPatchAlgebra. Pijul does something similar, claiming to have "a formally correct version of Darcs' theory of patches" https://pijul.org/manual/why_pijul.html

I've never used Pijul, but I miss Darcs almost every day when interacting with Git.