Dialogue protocol (PLAN P1): the ask-back form — at most 5 multiple-choice questions covering the unknowns that change the outcome most. Persisted.

ASK-ONCE (§2): blanks the lever registry already answers for this caller are PRE-FILLED (surfaced as prefilled, dropped from the ask list). On the caller's FIRST route in a session (first_route=true) the result carries one rules_prompt — the single constraint ask, surfaced never blocking (§1 elicitation).

verify_divergence=true (v2, opt-in — extra reduces, cache-aware): bind each option of the top 3 questions into the question, reduce each variant, and measure divergence (leaf-jaccard-v1). Zero divergence = noise-flagged; verified items re-ranked by measured divergence.