- missing_targets: List of target names with no saved model file on disk (eligible for first-time training). A model whose file exists but fails to deserialise raises OSError instead.
If a model file exists on disk but cannot be deserialised (corrupt joblib, version mismatch, etc.). The caller cannot silently retrain over a corrupt model — they must observe the failure and decide.
Save a single trained forecaster to disk using joblib.
Public single-model counterpart to save_forecasters(). When task_name is provided the file is named {task_name}_{target}.joblib; otherwise the standard convention forecaster_{target}.joblib (identical to get_model_filepath()) is used.