Prospective Grounding: When Proxy Diagnostics Warrant Control over Inference-Time Search

Inference-time search can increase proxy reward while losing content already satisfied by the current output. When should a diagnostic of this risk guide acceptance, verification, or refinement? We introduce the Prospective Grounding Certificate (PGC) to assess whether a diagnostic can guide decisions after search selection. It tests whether the diagnostic improves prediction, whether automatic outcomes reflect human judgment, and whether the resulting policy lowers semantic loss. A non-identification result establishes why repeatable proxy evidence cannot determine semantic downside without an outcome coupling. Before collecting outcomes, PGC screens out unattainable effects and unchanged actions. It then combines valid axis-wise tests to control family-wise false authorization. Controlled worlds isolate the role of each axis. In a text-to-image qualification analysis, 1,000 cases sampled from a 1,227-case frame received 3,000 blinded paired ratings. The reported predictions and labels satisfy all three declared criteria for the specified finite-frame policy. PGC makes explicit the evidence needed to connect a diagnostic's predictive role to the semantic value of the search decisions it informs.