Meaning we should feel free to ignore v3 and possibly a few later
versions, until we hear from you?

I pushed v4 now. Please feel free to review it.

And from what I read as _your_ use case in an earlier message,
init.defaultBranch aka @{default} is not what you want 999/1, yet I
think what the patch implements is still that one.  Puzzled...

I'm agnostic with the regards to the implementation as long as it solves
my problem.

I changed my mind after realizing the other approach would have required
me to set 'init.defaultBranch' on many repos -- or worse, badger the
maintainers to set it. That does not scale.

With the new approach, things run smoothly for all the repos on my machine,
so my goal of convenience is achieved there. I ran this to check that:

    for x in */*; do (
      cd "$x" && \
      echo && \
      echo "$x" && \
      /Users/Harald/git-repos/github.com/git/git/git checkout @{primary}
    ); done


Harald