Solution 1:

It can be shared via a dedicated branch. You want to stop if there is a conflict on that branch and resolve it as it means that there were attempts to solve the same conflict in 2 different ways. Needless to say, that will be the exception to the rule.

For the others on this question, google "Branch per Feature" to see where this is useful.

Hooks can automate syncing the common rr-cache branch.

Here is what you need to automate. rereresharing is an example branch that you are merging to, rr-cache is a branch that stores the resolutions; all these steps worked without issue:

git checkout --orphan rereresharing start-sprint-1 
git --git-dir=.git --work-tree=.git/rr-cache checkout -b rr-cache
git --git-dir=.git --work-tree=.git/rr-cache add -A
git --git-dir=.git --work-tree=.git/rr-cache commit -m "initial cache"
git clean -xdf
git checkout rereresharing 
git merge --no-ff FTR-1
git merge --no-ff FTR-2
vim opinion.txt # resolve conflict 
git add -A
git commit
git checkout rr-cache 
git --git-dir=.git --work-tree=.git/rr-cache add -A
git --git-dir=.git --work-tree=.git/rr-cache commit -m "resolution"
git remote add origin ../bpf-central
git push origin rereresharing rr-cache 
cd - # assumes you were previously in the other local repo
git remote add origin ../bpf-central
git fetch
git branch rr-cache origin/rr-cache 
ls .git/rr-cache
git --git-dir=.git --work-tree=.git/rr-cache checkout rr-cache -- .
ls .git/rr-cache

You are now ready to do the same merge and you will have your conflict resolved.

Solution 2:

Maybe instead of sharing rr-cache another option would be to learn the conflict resolutions from the existing Git history using rerere-train.sh.