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    FittedPreprocessing: Record<string, unknown>

    Serialized fitted-transform parameters (means/stds, one-hot vocabularies, bin edges, imputation fill values) produced by the sidecar at /train and replayed at /predict. The concrete shape is sidecar-defined and opaque to the orchestrator — it is stored verbatim on the trained model (MLModel.FittedPreprocessing, plan §4.3) and round-tripped unchanged.