From Model Coverage to Control Value: Auditing Few-Shot Safety Filters under Topology Shift

Safety filters are often judged by model error, yet a tighter model can be useless or uncertified: its error premise may fail, its reserve may empty the feasible set, or its rows may be inactive at the deployed decision. We introduce an optimizer-level, four-stage audit that separates model-premise validity, certificate availability, decision relevance, and control value. Under shared convex non-target constraints and a strictly convex objective, a single-solve certificate proves that every candidate constraint model whose feasible set contains a reference optimizer with strict target-row slack returns the same unique action; a computable perturbation radius extends the screen to a local model family. This certificate requires verified optimality and a shared problem, not voltage feasibility alone. We instantiate the audit for few-shot voltage shielding of electric-vehicle charging under topology shift using three complete target sensitivity queries. On three frozen feeders, interpolation upper-covers all 60/60 unqueried interior matrices and reduces final upper-bound overstatement by 38.74–61.96% relative to a same-budget baseline. The tighter model nevertheless changes no action in 34,560 comparisons: one of 15 base-feasible target–pressure layers fails zero-action voltage membership, and all remaining deployed actions have strictly inactive voltage rows. A prospectively frozen IEEE 8500 stress test covers only 3/20 matrices and therefore stops at the first gate; a state-binned reserve improves transfer coverage in 0/8 development comparisons and is not confirmed. The audit converts null and failed-transfer results into falsifiable diagnoses without treating finite-grid coverage as a population, arbitrary-topology, or nonlinear-AC guarantee.