Question about migrating things off GitHub: does it work to leave a mirror on GitHub as the "main" branch and still update it during transition, but change default-branch in the repo settings to a branch that just contains a "we've moved" README.md?
@slink Even if I don't want to keep updating a mirror, I'd rather (1) not break git state in a way that requires backing out history for someone who pulls an existing checkout without knowing about the move, and (2) not cause linkrot.
So an approach that leaves the (now no longer updated) branch in place is still preferable.