ansible-role-borg-backup/tasks/00_assert.yml

---
- name: Ensure legacy hooks aren't used
  ansible.builtin.assert:
    that:
      - borgmatic_failure_command is undefined
      - borgmatic_before_backup_command is undefined
      - borgmatic_after_backup_command is undefined
    msg: Please use the new borgmatic_hooks variable instead of individual before/after/failure hooks.
...