@startuml UC06_system_sequence
!theme plain
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skinparam sequenceMessageAlign center
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autonumber

title UC-06 — Boost cleaning when dust is high\n(system sequence diagram)

actor "Home user\n(beneficiary)" as User
participant "Dust / debris\nsensor" as Dust
box "Roomba RVC control software\n(black box)" #E8F4FF
  participant "System" as Sys
end box
participant "Cleaning hardware\n(vacuum, brushes, mop)" as Cln

note over User, Sys : after UC-01

alt [typical]
  Dust -> Sys : DustSignalUpdated(aboveThreshold)
  activate Sys
  Sys -> Cln : CleaningCommand(boost)
  Sys -> Cln : CleaningCommand(normal)
  deactivate Sys
  note over Sys : may overlap UC-02
else [A1 boost during suspended cleaning]
  Dust -> Sys : DustSignalUpdated(aboveThreshold)
  activate Sys
  Sys -> Cln : CleaningCommand(unchangedOrDeferredTBD)
  deactivate Sys
  note over Sys : cleaning suspended under UC-03 or UC-05
else [E1 invalid dust signal]
  Dust -> Sys : DustSignalUpdated(invalid)
  activate Sys
  Sys -> Cln : CleaningCommand(normal)
  deactivate Sys
  note over Dust, Cln : no boost; branch UC-08 if needed (TBD)
end

@enduml
