feat(multiplayer): handle planned shutdowns on clients

Game/scripts/networked_match.gd

@@ -321,6 +321,7 @@ var _max_spectators := -1
 var _last_emitted_countdown := -1
 var _in_overtime := false
 var _match_over := false
+var _planned_server_shutdown := false
 # Dedicated-export smoke hook (task 6.2). It is parsed only by the authoritative
 # server, cannot be triggered by an RPC, and defaults to disabled.
 var _smoke_force_goal_tick := -1
@@ -391,6 +392,7 @@ func _ready() -> void:
 		# is not connected" errors per run — it only ever left because a test
 		# timer happened to fire.
 		NetworkManager.disconnected_from_server.connect(_on_disconnected_from_server)
+		MatchNet.server_shutdown.connect(_on_server_shutdown)
 		_request_match_config_until_received()
 
 
@@ -994,12 +996,23 @@ func _broadcast_clock_state() -> void:
 
 
 func _on_disconnected_from_server() -> void:
+	if _planned_server_shutdown:
+		return
 	# Deferred: this arrives from inside NetworkManager's poll, and gotcha 27
 	# requires change_scene_to_file never run synchronously from a callback
 	# mid-traversal.
 	get_tree().change_scene_to_file.call_deferred(ScenePaths.MAIN_MENU)
 
 
+func _on_server_shutdown(reason: String) -> void:
+	if multiplayer.is_server() or _planned_server_shutdown:
+		return
+	_planned_server_shutdown = true
+	print("NetworkedMatch: server shutdown notice: %s" % reason)
+	NetworkManager.shutdown()
+	get_tree().change_scene_to_file.call_deferred(ScenePaths.LOBBY)
+
+
 func _on_match_bootstrap_received(state: int, at_tick: int, new_score: Dictionary, end_tick: int, clock_running: bool, reset_gen: int, remaining_ticks: int) -> void:
 	score = new_score.duplicate()
 	score_changed.emit(score.duplicate())