Leader 与 Candidate 配对
sequenceDiagram actor L as Leader participant LP as Leader Pairing participant T as Transport participant MP as Member Pairing actor M as Member L->>LP: start LP->>T: PairRequest T->>MP: request MP-->>M: confirm? M->>MP: confirm MP->>T: PairConfirm T->>LP: confirmed LP->>T: KeyDist T->>MP: keys