— name: rebase-onto-main description: Rebase a branch onto main, handling squash-merged parent branches cleanly argument-hint: "[optional: branch name, defaults to current branch]" allowed-tools: Bash, Read, Glob, Grep, Agent — # Rebase Branch onto Main Rebase the current (or specified) branch onto `main`, correctly handling the case where the branch was built on top of another branch that has since been squash-merged into `main`. ## Background When a parent branch is squash-merged, its individual commits become a single new commit on `main` with a different hash. A normal `git rebase main` will try to replay the parent's original commits, causing messy conflicts. The fix is to **cherry-pick only the commits unique to this branch** onto a fresh branch from `main`. ## Steps 1. **Identify the branch.** Use `$ARGUMENTS` if provided, otherwise use the current branch. 2. **Fetch and update main:** “` git fetch origin main:main “` 3. **Find the merge base** between the branch and `main`: “` git merge-base <branch> main “` 4. **List all commits** on the branch since the merge base: “` git log –oneline <merge-base>..<branch> “` 5. **Identify which commits are unique to this branch** vs. inherited from a parent branch. Look for: – Squash-merged commits on `main` that correspond to a group of commits at the bottom of the branch's history (check PR titles, commit message keywords). – The boundary commit: the first commit that belongs to *this* branch's work, not the parent's. – If ALL commits are unique (no parent branch), just do a normal `git rebase main` and skip the rest. 6. **Create a fresh branch from `main`:** “` git checkout -b <branch>-rebase main “` 7. **Cherry-pick only the unique commits** (oldest first): “` git cherry-pick <first-unique-commit>^..<branch> “` The `A^..B` range means "from the parent of A through B inclusive." 8. **Handle conflicts** if any arise during cherry-pick. Resolve and `git cherry-pick –continue`. 9. **Replace the old branch:** “` git branch -m <branch> <branch>-old git branch -m <branch>-rebase <branch> “` 10. **Verify** the result: “` git log –oneline main..<branch> “` Confirm only the expected commits are present. 11. **Ask the user** before force-pushing. When approved: “` git push origin <branch> –force-with-lease “` 12. **Clean up** the old branch: “` git branch -D <branch>-old “`