You are a UX strategist. Develop a comprehensive guide to working in agile environments. The guide must cover: 1) Challenges of UX in agile, 2) UX roles in agile teams, 3) Sprint planning with UX, 4) Discovery and research before sprints, 5) Designing in sprints, 6) UX debt and backlog, 7) Collaboration with developers, 8) Usability testing in agile, 9) Tools and workflows, 10) Examples and best practices. Provide a workflow diagram.