Training-boundary semantics for forward targets

The released target is forward-looking, while the platform passes a complete training prefix to Predictor.train. Are all target rows supplied to train considered fully realized and safe to use, including the final rows immediately before the prediction suffix? Or should a predictor internally embargo the target horizon before fitting? I will never read target in predict or use any future operation; I am asking only which supplied training rows are permitted to influence the first held-out predictions. Thanks.