If you haven't done *any* git missions, this page tells you to go back to the
"Creating a patch" mission. But there are two other dependencies of the rebase
I'd either continue checking the dependencies of all the prerequisite missions,
and send the user back to the first one, or *start* at the first mission in that
category, check the later ones, and return the first one the user hasn't done. I
don't know if multiple prerequisites are possible or desirable, though, so the
latter choice might not be helpful.
This would definitely cut the number of page loads per attempt at accessing a
mission they can't do yet.