The project I’m working, repo A was copied (not forked) and used as a base in a different project, repo B. These are now two distinct repositories, which originally shared a common commit. repo B is 800 commits in and repo A is 60 commits in, since their original commit.

Now that the problem was discovered, we want to configure repo B as a fork of repo A, pull all changes from repo A and then apply the changes made on repo B.

Initially, I though of creating patches based on repo B and applying them on a forked repo A. But at 800 commits, this seems like a tedious task and certainly not error proof.
Then I though of trying the other way around and applying the commits from repo A to repo B, but while this isn’t so tedious, there wouldn’t be a correspondance between the original commits in repo A and those applied on top of repo B because now repo B has its own changes.

So now I’m thinking of creating a fork of repo A and then slowly and painfully integrate the changed files (not the commits), of repo B into the new repository and thus recreate the repository. It’s just sad …

Is there a better way for configuring repo B as fork for the latest repo A and then applying the changes of repo B? Keep in mind they have a common original commit.