@startuml
!include card-uml-style.iuml
scale 900 width
left to right direction

class "01  peerA\npriority 2 · CPU-bound" as PeerA <<task>>
class "02  peerB\npriority 2 · CPU-bound" as PeerB <<task>>
class "03  high_probe\npriority 0 → 3" as High <<task>>
class "04  verifier\npriority 1 · runs last" as Verifier <<task>>

PeerA <--> PeerB : tick time slicing\nA → B → A
PeerA --> High : raise to priority 3
High --> PeerA : preempts before call returns
PeerA --> Verifier : stop requested after return
PeerB --> Verifier : both peers self-delete

note right of High
  HIGH writes marker 2 and self-deletes.
  peerA then writes marker 3.
end note
@enduml