Closing layer: turn a decision question into a SCORED decision frame (objective / decision_rule / criteria / scored candidates / ranked / recommendation) plus needs[] (what to fetch) and ask_user[] (what only the human can supply). The algorithm in reduce.decide_question.

retrieval is executed by the calling agent via MCP; this endpoint returns the decision frame + what to fetch. Service-side has no web tools, so retrieve stays None — the response carries the scored scaffold + needs[].