# Step 0: Detect Base Branch

Determine which branch this PR targets. Use the result as "the base branch" in all subsequent steps.

1. Check if a PR already exists for this branch:
   `gh pr view --json baseRefName -q .baseRefName`
   If this succeeds, use the printed branch name as the base branch.

2. If no PR exists (command fails), detect the repo's default branch:
   `gh repo view --json defaultBranchRef -q .defaultBranchRef.name`

3. If both commands fail, fall back to `main`.

Print the detected base branch name. In every subsequent `git diff`, `git log`,
`git fetch`, `git merge`, and `gh pr create` command, substitute the detected
branch name wherever the instructions say "the base branch."
