feat: implement the new "Stop N Go" game mode, including phase management, dynamic safe zones, player missions, and dedicated UI with visual effects.

scenes/player.gd

@@ -621,10 +621,13 @@ func receive_spawn_positions_update(occupied_positions: Array):
 			highlighted_spawn_points.erase(pos)
 			if enhanced_gridmap:
 				# Clear the highlight from Layer 2 (Overlay) instead of overwriting Floor 0
-				enhanced_gridmap.set_cell_item(
-					Vector3i(pos.x, 2, pos.y),
-					-1
-				)
+				# PROTECTION: Never clear if it's a Safe Zone (ID 2)
+				var current_l2 = enhanced_gridmap.get_cell_item(Vector3i(pos.x, 2, pos.y))
+				if current_l2 != 2:
+					enhanced_gridmap.set_cell_item(
+						Vector3i(pos.x, 2, pos.y),
+						-1
+					)
 	
 	# Now highlight available positions
 	highlight_available_spawn_points()