Git worktree metadata in .git/worktrees/{name} has a 'commondir' file
that references back to the parent .git directory (typically '../..').
Mounting just the worktrees subdirectory wasn't sufficient - we need
to mount the entire .git directory so that:
1. The worktree's .git file can resolve to .git/worktrees/{name}
2. The commondir reference can resolve back to the main .git
3. Git objects, refs, and other shared data are accessible
jcfs
3c460a694b