When the home interface is connected, .git is allowed in any subdirectory of ~ (eg, /home/user/projects/blah/.git). $HOME is set to SNAP_USER_DATA so snaps will have access to ~/snap/name/revision/.gitconfig and ~/snap/name/revision/.ssh. If people insist on having git access all their ssh keys rather than just snap-specific keys in SNAP_USER_DATA, we have an ssh-keys interface that can be used.
It seems like a snap author has everything a typical ‘snap that uses git’ would need-- can you give specific examples of snaps that are classic because there is no git interface?