feat(sfx): add looping ambient heartbeat to UltrasoundMachine

scripts/objects/ultrasound_machine.gd

@@ -1,4 +1,5 @@
 ## UltrasoundMachine — displays a continuous heartbeat pulse on the screen.
+## Plays looping ambient heartbeat audio when the ultrasound room is active.
 class_name UltrasoundMachine extends Node2D
 
 const BEAT_RISE_DURATION: float = 0.12
@@ -6,10 +7,46 @@ const BEAT_FALL_DURATION: float = 0.12
 const BEAT_INTERVAL: float = 0.60
 const BEAT_SCALE_PEAK: Vector2 = Vector2(1.5, 1.5)
 const BEAT_SCALE_REST: Vector2 = Vector2(1.0, 1.0)
+const _HEARTBEAT_PATH: String = "res://assets/audio/sfx/ultrasound_heartbeat.ogg"
+
+@export var trigger_floor: int = 2
+@export var trigger_room: int = 0
+
+var _audio: AudioStreamPlayer
 
 
 func _ready() -> void:
 	_start_heartbeat_loop()
+	_setup_audio()
+	RoomNavigator.room_changed.connect(_on_room_changed)
+
+
+func _exit_tree() -> void:
+	if RoomNavigator.room_changed.is_connected(_on_room_changed):
+		RoomNavigator.room_changed.disconnect(_on_room_changed)
+
+
+func _setup_audio() -> void:
+	_audio = AudioStreamPlayer.new()
+	add_child(_audio)
+	if AudioServer.get_driver_name() == "Dummy":
+		return
+	if not ResourceLoader.exists(_HEARTBEAT_PATH):
+		return
+	var stream: AudioStreamOggVorbis = load(_HEARTBEAT_PATH) as AudioStreamOggVorbis
+	if stream == null:
+		return
+	stream.loop = true
+	_audio.stream = stream
+
+
+func _on_room_changed(floor_index: int, room_index: int) -> void:
+	if _audio == null or _audio.stream == null:
+		return
+	if floor_index == trigger_floor and room_index == trigger_room:
+		_audio.play()
+	else:
+		_audio.stop()
 
 
 func _start_heartbeat_loop() -> void: