Stagewise Variable Selection for Joint Models of Semi-Competing Risks // Implements stagewise regression for variable selection in joint models of recurrent events and terminal events (semi- competing risks). Supports two model frameworks: the joint frailty model (Cox-type) and the joint scale-change model (AFT- type). Provides cooperative lasso, lasso, and group lasso penalties with cross-validation for tuning parameter selection via cross-fitted estimating equations.