Expand description
jj backend for the Vcs trait: a colocated jj/git repo (.jj beside
.git, as jj git init --colocate makes). Reads delegate to GitVcs,
since a colocated repo keeps git’s HEAD on jj’s @- and the working
copy on disk matches @, so diff, log, blame, and tree reads already
answer correctly through git2. Writes shell out to the jj CLI: jj owns
the operation log and working-copy snapshot, and duplicating that through
git2 would fight the real source of truth.