The Feature at the Ceiling: Counting Saturation Predicts a Break in the Cosmic-Ray Spectrum at 3.02e18 eV - and the Instrument That Settles It

Counting saturation caps independent modes at E_ind = 3.02e18 eV, fixed by the vacuum programme before any look at the cosmic-ray spectrum. The cap is a spectral event: the paper predicts a slope break within +-0.1 dex of 3.02e18 eV (0.604x the ankle, resolvable at Auger-class energy resolution) and designs the instrument that settles it - a blinded, pre-registered re-analysis with the break position fixed in advance. Detection simulation (SIMULATED, NOT MEASURED): an ankle-sized hardening step reaches detection class at 3e4 events above 1e18 eV and is invisible at 3e3; the marginal exposures are printed at full size.