@startuml uc-10-practice-bard-song
autonumber
title UC-10 Practice Bard Song (design sequence)
actor Player
participant "SongBoundary\n«/api/characters/{id}/songs»" as boundary <<boundary>>
participant "SongService\nsb-api::routes::set_song" as control <<control>>
participant "BardSong\nBARD_SONGS + active_song" as entity <<entity>>

== View ==
Player -> boundary : GET songs
boundary -> entity : available_songs (level-gated)
boundary --> Player : songs + effects + active song

== Set / Clear ==
Player -> boundary : POST song id (or empty to clear)
boundary -> control : set_song(character, song)
alt non-Bard
  control --> boundary : 403
else unknown song
  control --> boundary : 404
else level too low
  control --> boundary : 422
else ok
  control -> entity : active_song = song (or None), persist
  control --> boundary : {success, message, active_song}
  boundary --> Player : {success, message, active_song}
end
note over entity : active song applies in UC-08 combat (step 5)
@enduml