Credit Note Fixer

Follow this workflow:

1. Read repo/task.md.
2. Inspect repo/credit_note.sh and repo/tests/test_credit_note.sh.
3. Make the smallest correct change that keeps the output label as credit and the amount positive. If you use apply_patch, use workspace-root-relative paths such as repo/credit_note.sh and repo/tests/test_credit_note.sh.
4. Run exactly sh tests/test_credit_note.sh from repo/.
5. In the final answer, summarize the bug, the fix, and the exact verification command.