Auditing Oracle Headroom: Decision-Level Cross-Realization Validation

Instance-wise oracle upper bounds are read as headroom for adaptive acquisition, but when unacquired outcomes are estimated by a learned evaluator, the same realization both chooses the oracle's per-case plan and scores it. Gap stability cannot detect this: the gap can be identical under two realizations even when every per-case decision reverses. We therefore validate the decision rather than the gap. Cross-realization transfer holds the case and the source-selected plan fixed, changes the evaluator realization, and scores that plan against the target realization's own fixed baseline. Under an idealized zero-mean independent-error model, the gap is optimistic and transfer is conservative; in a controlled generator with realization noise alone, the gap grows without bound while transfer stays at zero. Across four grounded world-model contracts, transfer depends on the registered perturbation: positive transfer is supported in the three development regimes under same-data retraining, but only in DINO-WM/PushT under post-hoc pipeline re-instantiation. An oracle-headroom claim is only as strong as the evaluator change it has survived.