Jeremy Rosen [off-list ref] writes:
is there a way to "teach" rerere about existing merge commits, or do I
have to re-solve all the existing merge manually once ?
There is a tool that does the "re-solve manually" for you.
$ git ls-files | grep rerere-train
contrib/rerere-train.sh
It uses your working tree to do its work, so you should first commit
or stash whatever you are in the middle of doing before using it.