Universal Efficiency Bound for Irreversible Decisions at Criticality

We prove that no irreversible decision or measurement performed on a critical stochastic system can exceed efficiency η = 1/e, and this bound is saturated uniquely at criticality (σ = 1). The result is structural, not dynamical: criticality eliminates characteristic scales, forcing decision-making into the secretary problem framework where 1/e emerges universally. Weestablish uniqueness of the optimal point, stability under perturbations, and the global bound η(σ) ≤ 1/e with equality if and only if σ = 1. The bound arises from symmetry constraints rather than equations of motion.