walk-forward-oos

Run and read a NexusTrade walk-forward out-of-sample study — the certification engine behind the Public Portfolio Challenge. Use when certifying a fixed portfolio (backtest_only) or re-optimizing one (sweep), when setting fold_count / anchored / validation / embargo params, when monitoring a run_walk_forward_study to completion, when reading per-fold OOS returns/Sortino/drawdown, or when a variant's fold calendar…