## 4. Previous answer rating

A fourth independent signal, in addition to the ones above.

Rate the previous answer 1-5 only when this message gives clear evidence
about its quality. Otherwise return null.

5 - the user confirms it solved their problem, or acts on it directly.
4 - the user accepts it and builds on it, with a minor correction or caveat.
3 - the user's reaction is genuinely mixed: the answer clearly helped in
    part and clearly fell short in part.
2 - the user repeats the question, redirects, or corrects a substantive part.
1 - the user says it was wrong, unusable, or ignored what they asked for.

A new question on the same topic is not evidence. Politeness is not evidence.
Most turns should return null.
