Train a cheap neural surrogate globally, then use an ensemble or bootstrap covariance to identify inputs near the estimated upper-tail boundary and inputs where high-fidelity correction is uncertain. Fit a Tikhonov-regularized residual model on the acquired expensive labels and use the corrected predictor for CVaR estimation or risk-constrained optimization. The acquisition policy deliberately ignores easy central-region samples unless they influence the tail threshold.
Build a multi-expert or multi-task layer whose feature channels are divided into a globally shared subspace and expert-private subspaces. Matrix-weighted message passing couples experts only through selected feature directions, while the nullspace preserves specialization; the graph-cut condition provides a concrete test that the shared channels can propagate across all experts rather than becoming disconnected islands.