The opening brief has been filed in a Fourth Circuit appeal that’s sure to be closely watched by the 100,000 members of the D.C. bar, as well as others. A key issue in Moskowitz v. Jacobson Holman PLLC is whether a law firm partnership agreement can reduce a partner’s equity payout if the partner walks out the door with clients. The district court said that the provision violates ethics rules, and is therefore unenforceable as against public policy.…