The Rule
The original prompt constrained answer refinement to two outcomes. If the new context is useful, rewrite the answer using it. If the new context is not useful, repeat the original answer.
That keeps retrieval from becoming automatic contamination. A retrieved passage has to earn its way into the answer.
The Small Test
The prompt example used a simple fact: "Three apples were green." The query asked what color the apples were. The model's job was not to discuss context. It was to produce the corrected answer when the context answered the query.
The same discipline scales to larger RAG systems: context should either change the answer for a reason or leave the answer alone.