@startuml
skinparam shadowing false

actor User
participant "WriteRouteMap" as WR
participant "RangePartition" as P
participant "Active Mutable Layer" as M
participant "Immutable Queue" as Q
participant "Background Flush" as F

User -> WR : put(key, value)
WR -> P : resolve partition
P -> M : insert

alt active has room
  P --> User : OK
else rotate possible
  P -> Q : move old active to immutable
  P -> M : create new active
  P --> User : OK
  F -> Q : flush oldest immutable
else immutable queue full
  P --> User : throttle / short stall / OVERLOADED
end

@enduml