"The district court concluded that the fiduciary breach claims against Ruane related to Cooper's employment with DST and that Ruane -- a non-signatory to the arbitration agreement -- was entitled under equitable estoppel to enforce the agreement against Cooper. The Second Circuit reversed[.]" [Cooper v. Ruane Cunniff & Goldfarb Inc., No. 17-2805 (2d Cir. Mar. 4, 2021)]