If the parties wish to provide for the court's enforcement of a dismissal-producing settlement agreement, they can seek to do so. When the dismissal is pursuant to Federal Rule of Civil Procedure 41(a)(2), which specifies that the action "shall not be dismissed at the plaintiff's instance save upon order of the court and upon such terms and conditions as the court deems proper," the parties' compliance with the terms of the settlement contract (or the court's "retention of jurisdiction" over the settlement contract) may, in the court's discretion, be one of the terms set forth in the order. Even when, as occurred here, the dismissal is pursuant to Rule 41(a)(1)(ii) (which does not by its terms empower a district court to attach conditions to the parties' stipulation of dismissal) we think the court is authorized to embody the settlement contract in its dismissal order (or, what has the same effect, retain jurisdiction over the settlement contract) if the parties agree. Absent such action, however, enforcement of the settlement agreement is for state courts, unless there is some independent basis for federal jurisdiction.