接听与资源独占

sequenceDiagram
participant L as LXST
participant C as Call Runtime
actor U as 用户
participant A as Resource Access
participant M as Audio Engine
L->>C: incoming + ringing
C->>A: soft preempt
U->>C: accept
C->>A: exclusive
L->>C: link active
C->>M: start
M-->>C: ready/failed