I don't think so. I just re read the git-scm-tagging
just to confirm your this statement
a tag is a line segment of a branch so it has a defined start and a defined endpoint.
It's just another way to name a commit, you can do git show <tag name> instead of commit hash and it will show you that commit. Which means it's not a line segment, it's a point that's all.
it's one way to define 'stable' reproducible packages.
I do agree with this one though.
Let me know if I am correct. Tag is one of the lesser used features of git and requires a bit of understanding before one can get mastery over it