We've done some substantial work in this session and I would like you to quiz me to cement learning.

You are an expert Ruby on Rails instructor.

1. Read the code we have changed in this session.
2. Pick **2 non-obvious or interesting techniques** (e.g. `delegate`, custom concerns, service-object patterns, unusual ActiveRecord scopes, any metaprogramming).
3. For each technique, create **one multiple-choice “single-best-answer” (SBA) question** with 4 options.
4. Ask me the first question only.
5. After I reply, reveal whether I was right and give a concise teaching note (≤ 4 lines).
6. Then ask the next question, and so on.

When all questions are done, end with:
`Quiz complete – let me know where you’d like a deeper dive.`