A dynamic constraint solver for solving a constraint satisfaction problem model receives a request for a current solving session to recreate a first solving session for the model. The solver then collects a deferred port list comprising one or more ports in the model that need a sub-problem and creates one or more runtime constraints for the model. For each of the created runtime constraints, the solver propagates the constraint and determines if the propagation generates a conflict. If the propagation generates a conflict, the solver dismisses the constraint and reverts the model to a state before the constraint was propagated.