Decoder-Agnostic Logical-Error Reduction from Budget-Matched Heterogeneous Pre-Decoder Conditioning in Surface-Code Quantum Error Correction

This registration describes a preregistered confirmatory study of heterogeneous pre-decoder conditioning in a rotated surface-code quantum error-correction workflow. Its purpose is to test whether, at a fixed total conditioning budget, heterogeneously distributed upstream conditioning produces lower logical error than budget-matched uniform conditioning, whether a single frozen conditioned representation remains effective across an architecture-diverse downstream decoder set, and whether performance varies nontrivially across a preregistered ordered target:non-target ratio grid. The study is conducted under frozen distances, frozen operating points, frozen seed and shot schedules, preregistered pooled metrics, and locked success criteria so that any supported effect can be interpreted as evidence about the architecture under test rather than post hoc tuning. The design contains four preregistered arms: untreated control, budget-matched uniform conditioning, budget-matched differential conditioning, and an ordered ratio-sweep arm with fixed total burden. A central feature of the protocol is that the conditioned representation is formed once upstream and then passed unchanged to each confirmatory decoder family, with no decoder-specific retuning, remapping, or auxiliary adaptation permitted after formation. The minimum confirmatory decoder set is minimum-weight perfect matching, Union-Find, and BP+OSD, selected to evaluate transfer across structurally different decoder families. Expected outcomes are defined in confirmatory terms. The primary pooled causal endpoint tests whether budget-matched differential conditioning outperforms budget-matched uniform conditioning, while the primary pooled transfer endpoint tests whether the same frozen conditioned representation improves performance relative to untreated control across decoder families. Additional preregistered questions address tunability through the ordered ratio response and persistence of favorable pooled effects across more than one primary code distance. A strong confirmatory outcome requires favorable pooled results with two-sided 95% bootstrap confidence intervals excluding 1 in the favorable direction, plus distance persistence at two or more primary distances; mixed, null, and thesis-changing outcomes are also explicitly predefined. This registration is limited to architecture-level evaluation and reproducible public inference. It does not claim that the frozen partition rule is uniquely optimal, that any specific targeting heuristic is the sole source of benefit, that threshold or asymptotic scaling is established, or that the exact coupling law, score function, or targeting recipe is disclosed. The confirmatory claim is bounded to whether budget-matched heterogeneous upstream conditioning improves logical performance and transfers across decoder families when the upstream representation is held fixed.