I did clone a repository main to secondary two months ago. The two repositories have many branches.
I am sure that many branches of main has been update by new commits (let’s admit that I don't know witch branch has been updated). And I know that the secondary has not been modified since my last clone.
I want to merge all branches of my main branch to the secondary branch without losing history (dropping all modification that has been done in the main branch to the secondary branch).
I've already spent a lot of time reading the Git User's Guide and so on. However, this (special) case of use doesn't seem to be documented anywhere.