2 files changed, 83 insertions, 0 deletions

diff --git a/internal/world/mob.go b/internal/world/mob.go
index f33b2f9..a794bdd 100644
--- a/internal/world/mob.go
+++ b/internal/world/mob.go
@@ -722,3 +722,27 @@ func (s *MobStore) SeedMobs(roomID int, entries []RoomMob) {
 		s.instances[instID] = inst
 	}
 }
+
+// RekeyRooms remaps every live mob instance's RoomID and HomeRoomID per
+// idMap (oldID -> newID), including wander rooms. Uses delete-all-then-
+// set-all so a swap cannot clobber an entry mid-rekey.
+func (s *MobStore) RekeyRooms(idMap map[int]int) {
+	if len(idMap) == 0 {
+		return
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	for _, inst := range s.instances {
+		if newID, ok := idMap[inst.RoomID]; ok && newID != inst.RoomID {
+			inst.RoomID = newID
+		}
+		if newID, ok := idMap[inst.HomeRoomID]; ok && newID != inst.HomeRoomID {
+			inst.HomeRoomID = newID
+		}
+		for i, room := range inst.WanderRooms {
+			if newID, ok := idMap[room]; ok && newID != room {
+				inst.WanderRooms[i] = newID
+			}
+		}
+	}
+}
diff --git a/internal/world/world.go b/internal/world/world.go
index b582faf..c5d0841 100644
--- a/internal/world/world.go
+++ b/internal/world/world.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"sync"
 
@@ -175,3 +176,61 @@ func (w *World) ClearRoomState(roomID int) {
 		}
 	}
 }
+
+// RekeyRooms remaps room-keyed runtime state per idMap (oldID -> newID):
+// ground items, seeded markers, and object-state keys ("roomID:...").
+// Uses delete-all-then-set-all so a swap cannot clobber an entry mid-rekey.
+func (w *World) RekeyRooms(idMap map[int]int) {
+	if len(idMap) == 0 {
+		return
+	}
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	movedGround := make(map[int][]*groundEntry, len(w.groundItems))
+	for roomID, entries := range w.groundItems {
+		if newID, ok := idMap[roomID]; ok && newID != roomID {
+			movedGround[newID] = entries
+			delete(w.groundItems, roomID)
+		}
+	}
+	for newID, entries := range movedGround {
+		w.groundItems[newID] = entries
+	}
+	movedSeeded := make(map[int]bool, len(w.seeded))
+	for roomID := range w.seeded {
+		if newID, ok := idMap[roomID]; ok && newID != roomID {
+			movedSeeded[newID] = true
+			delete(w.seeded, roomID)
+		}
+	}
+	for newID := range movedSeeded {
+		w.seeded[newID] = true
+	}
+	type objKeyMove struct {
+		oldKey, newKey string
+		st             *ObjState
+	}
+	var moves []objKeyMove
+	for k, st := range w.objStates {
+		roomStr, _, ok := strings.Cut(k, ":")
+		if !ok {
+			continue
+		}
+		roomID, err := strconv.Atoi(roomStr)
+		if err != nil {
+			continue
+		}
+		newID, ok := idMap[roomID]
+		if !ok || newID == roomID {
+			continue
+		}
+		newKey := fmt.Sprintf("%d:%s", newID, k[len(roomStr)+1:])
+		moves = append(moves, objKeyMove{k, newKey, st})
+	}
+	for _, m := range moves {
+		delete(w.objStates, m.oldKey)
+	}
+	for _, m := range moves {
+		w.objStates[m.newKey] = m.st
+	}
+}