C.19:4.2 - Closure rule over the live pool

A C.19 pass may close only when one explicit pool and one explicit next treatment are both visible.

• Close as widen when wider exploration is warranted under the pool’s contribution, horizon and resource conditions. If widening also asserts a wider supported use, satisfy that use’s graduation and assurance conditions.
• Close as keep_frontier when keeping the live lines is warranted under the current policy. A line retained for later reconsideration need not receive a new probe.
• Close as narrow_to_subset when the continuation basis warrants a smaller internal live set, without pretending that one scalar winner has already been chosen.
• Close as sunset_line when a line’s prospective contribution, feasible continuation or retention no longer warrants its burden under the pool policy. Failure to graduate is not enough. Its archived result may still be retained under C.18 when that separate retention remains useful.

When the question has stopped being pool policy, finish the pool-policy result and use the exact handoff in C.19:4.4; the next pattern is recorded outside currentTreatment.

One internal retained subset here is still one pool-treatment result. It is not yet a declared Shortlist or RankedShortlist, and it has no ShortlistId merely by being retained. When a downstream use needs declaration or audience availability, use C.19:4.4.

If the result still cannot say which pool remains live, which lens and policy apply, and which event would justify changing the treatment, it is still unfinished pool policy rather than one finished C.19 result.