Rebase would mean only one of those two things is real and true in the history, and it’s whatever the last thing was. The other one has no SHA or commits in history anywhere anymore and is essentially erased whenever the gitlog does a gc.

Merging is correct I believe (at least in this context), as you alluded to. But a rebase means only one version of summer exists, not another summer. And there’s no record of that first summer ever existing after a -f push.