Gotcha: Git rebase can duplicate commits when shared

After rebasing a branch that others have already pulled, pushing creates duplicate commits or forces everyone to re-clone.

Never rebase commits that have been pushed and shared with others.

Safe rebase rules:

1. Only rebase YOUR LOCAL unpushed commits
2. If the branch is shared (PR open, others pulled): use merge instead
3. If you must rebase a shared branch: coordinate with all users

If you already rebased a shared branch:

1. Force push: git push --force-with-lease (safer than --force)
2. Tell everyone to:

git fetch origin
git reset --hard origin/branch-name
# OR if they have local changes:
git rebase origin/branch-name

Safe workflow for personal feature branches:
git fetch origin
git rebase origin/main # rebase YOUR branch onto latest main
git push --force-with-lease # safe if only you use this branch

Rebase rewrites commit hashes. If others have the old hashes, git sees them as different commits, creating duplicates.