Space transitions now automatically set up as turfs change

code/game/turfs/space/space.dm

@@ -23,6 +23,16 @@
 /turf/space/Destroy()
 	return QDEL_HINT_LETMELIVE
 
+/turf/space/PreChange()
+	..()
+	var/datum/space_level/S = space_manager.get_zlev(z)
+	S.remove_from_transit(src)
+
+/turf/space/AfterChange(ignore_air, keep_cabling = FALSE)
+	..()
+	var/datum/space_level/S = space_manager.get_zlev(z)
+	S.add_to_transit(src)
+
 /turf/space/proc/update_starlight()
 	if(!config.starlight)
 		return
@@ -69,7 +79,7 @@
 
 /turf/space/Entered(atom/movable/A as mob|obj, atom/OL, ignoreRest = 0)
 	..()
-	
+
 	if(destination_z && A && (src in A.locs))
 		A.x = destination_x
 		A.y = destination_y

code/game/turfs/turf.dm

@@ -165,6 +165,7 @@
 	var/old_blueprint_data = blueprint_data
 	var/old_obscured = obscured
 
+	PreChange()
 	if(air_master)
 		air_master.remove_from_active(src)
 	var/turf/W = new path(src)
@@ -186,11 +187,14 @@
 			lighting_build_overlays()
 		else
 			lighting_clear_overlays()
-	
+
 	obscured = old_obscured
 
 	return W
 
+/turf/proc/PreChange()
+	return
+
 // I'm including `ignore_air` because BYOND lacks positional-only arguments
 /turf/proc/AfterChange(ignore_air, keep_cabling = FALSE) //called after a turf has been replaced in ChangeTurf()
 	levelupdate()

code/modules/space_management/space_level.dm

@@ -28,28 +28,47 @@
 	var/timer = start_watch()
 	log_debug("Starting to build space destination arrays for z level '[zpos]'...")
 	for(var/turf/space/S in get_turfs())
-
-		// Bottom border
-		if(S.y <= TRANSITIONEDGE)
-			transit_south |= S
-			continue
-
-		// Top border
-		if(S.y >= (world.maxy - TRANSITIONEDGE - 1))
-			transit_north |= S
-			continue
-
-		// Left border
-		if(S.x <= TRANSITIONEDGE)
-			transit_west |= S
-			continue
-
-		// Right border
-		if(S.x >= (world.maxx - TRANSITIONEDGE - 1))
-			transit_east |= S
-			continue
+		add_to_transit(S)
 	log_debug("Building space destination arrays complete, took [stop_watch(timer)]s.")
 
+/datum/space_level/proc/add_to_transit(turf/space/S)
+	if(S.y <= TRANSITIONEDGE)
+		transit_south |= S
+		return
+
+	// Top border
+	if(S.y >= (world.maxy - TRANSITIONEDGE - 1))
+		transit_north |= S
+		return
+
+	// Left border
+	if(S.x <= TRANSITIONEDGE)
+		transit_west |= S
+		return
+
+	// Right border
+	if(S.x >= (world.maxx - TRANSITIONEDGE - 1))
+		transit_east |= S
+
+/datum/space_level/proc/remove_from_transit(turf/space/S)
+	if(S.y <= TRANSITIONEDGE)
+		transit_south -= S
+		return
+
+	// Top border
+	if(S.y >= (world.maxy - TRANSITIONEDGE - 1))
+		transit_north -= S
+		return
+
+	// Left border
+	if(S.x <= TRANSITIONEDGE)
+		transit_west -= S
+		return
+
+	// Right border
+	if(S.x >= (world.maxx - TRANSITIONEDGE - 1))
+		transit_east -= S
+
 /datum/space_level/proc/get_turfs()
 	return block(locate(1, 1, zpos), locate(world.maxx, world.maxy, zpos))