Subject identity leaks into biosignal classifiers: a multi-dataset audit, a pre-training risk index and an open-source toolkit

Preprint (author's original manuscript) submitted to Biomedical Engineering / Biomedizinische Technik on 26 September 2026; not yet peer reviewed. Code, the leakscope Python package and all replication materials: https://doi.org/10.5281/zenodo.22974070 Objectives: Machine-learning studies on physiological signals often let segments from the same person appear in both training and test data. We quantified when and how much such subject leakage inflates reported performance, and how often it occurs.