feat: add validated quicksave persistence

tests/npc_visual_lifecycle_test.gd

@@ -99,6 +99,23 @@ func _run() -> void:
 		"Active position callback should synchronize simulation state"
 	)
 
+	var saved_state: String = manager.serialize_state()
+	var visual_before_restore: Node3D = view.active_npc_visuals[npc.id]
+	npc.hunger = 99.0
+	_check(
+		manager.restore_state_from_json(saved_state),
+		"Visual lifecycle scenario should restore valid state"
+	)
+	var visual_after_restore: Node3D = view.active_npc_visuals[npc.id]
+	_check(
+		visual_after_restore != visual_before_restore,
+		"State restoration should rebuild active NPC presentation"
+	)
+	_check(
+		visual_after_restore.global_position.is_equal_approx(npc.position),
+		"Rebuilt presentation should use the restored authoritative position"
+	)
+
 	if failures.is_empty():
 		print("[TEST] NPC visual lifecycle passed")
 		quit(0)