rerere is indeed bolted on. Linus doesn’t want people who he pulls from to back-merge, i.e. to merge at “random points” from him into their trees to keep up to

rerere is indeed bolted on. Linus doesn’t want people who he pulls from to back-merge, i.e. to merge at “random points” from him into their trees to keep up to date. But what about merge conflicts? Then he has to deal with them. So then he might begrudgingly ask them to back-merge right before making a pull: a real zig-zag pattern. First-class conflicts would solve all that I think.