Get Agent Discovery Campaign Brief

The campaign brief the record would produce. A PREVIEW - it writes nothing.

Deterministic and LLM-free: running it again after two more answers gives the same document plus two facts, not a differently-worded one. That is what makes it safe to poll while the interview is still going.

It never fills a gap to look finished. open_musts and assumptions come back alongside the copy, because a brief that reads as complete while four must-answer questions are open is how a silent gap becomes a confident wrong campaign.