Beyond Readiness: Operator-Conditioned Answer Closure in Streaming Evidence

A supported answer can still change as a stream continues. We formalize operator-conditioned answer closure: a supported candidate is closed when every continuation admitted by the question operator and horizon preserves it. Four reference states distinguish absent support, provisional support, closure, and terminal unanswerability; calibrated gates derive response actions. Operator-balanced shared-prefix streams provide exact symbolic labels for comparing learned estimators across seven controllers. On 1,440 held-out symbolic trajectories from known program families, a gap-aware GRU reaches 0.9954 closure average precision and 0.9851 state macro-F1. Relative to an event-time survival baseline, it reduces premature commitment from 0.0040 to 0.0008 at identical answer coverage. Normalized delay, however, increases from 0.0612 to 0.0683, and same-target controls show no uniform ranking advantage from finer state supervision. With frozen VideoLLM features, a human-reviewed video pilot yields closure AP 0.9180 but fixed-four-class macro-F1 0.2900. Its seven held-out video records come from two source components and contain no terminal-unanswerable reference labels. These results distinguish current support from answer finality and show why closure ranking, state classification, and stopping quality require separate evaluation.