@startuml UC01_system_sequence
!theme plain
hide footbox
skinparam sequenceMessageAlign center
skinparam responseMessageBelowArrow true
skinparam BoxPadding 10
autonumber

title UC-01 — Start automatic cleaning session\n(system sequence diagram)

actor "Home user\n(or Scheduler)" as Who
box "Roomba RVC control software\n(black box)" #E8F4FF
  participant "System" as Sys
end box

alt [typical]
  Who -> Sys : StartSession(source)
  note over Who, Sys : next: UC-02
else [A1 start ignored]
  Who -> Sys : StartSession(source)
  Sys --> Who : start rejected
else [A2 resume after pause]
  Who -> Sys : ResumeSession(source)
  note over Who, Sys : may re-enter UC-01; TBD
else [E1 command lost]
  Who -> Sys : StartSession(source)
  Sys --> Who : no acknowledgement received
end

@enduml
