Git - updating branches on an error in the core of the project

Question

git

Let's say that we are writing 2 projects (directories "project1", "project2") with a common core (folder "core") - we have two branches in git that do not know about each other, nothing but the very first commit of the core.
During the development of one of them, we find a big error (not one line and not one file) in the kernel.
How to update the second project correctly?

Answer 1

As an option, move the core to a separate repository and connect it to project1 and project2 as a submodule