Auditing Syndrome-to-Decoder Mappings for Repetition, Surface, CSS, and Digitized-GKP Interfaces

Quantum error-correction experiments increasingly require a verified interface between measured syndrome bits and decoder-native correction requests. We report a four-branch syndrome-to-decoder mapping audit spanning a five-data-qubit repetition code, a distance-five surface Z-check interface, a compact Steane CSS benchmark, and a digitized-GKP proxy. For the surface interface, an independent noiseless interpreter verifies 40/40 single-X syndrome columns and data-bit round trips, while a reversed-register negative control fails for all 40 targets. Sampled hardware and local-noise streams are then analyzed with exact binary minimum-weight representatives to separate mapping validity from noisy localization. The results establish a narrow interface-conformance claim, not a decoder benchmark, threshold estimate, or logical-QEC demonstration.