fix: address bug-hunt findings across security, concurrency, trade & wired

Security
- HousekeepingSetUserRankEvent: add rank-ceiling guard (reject granting a
  rank above the operator's own and modifying a higher-ranked target),
  mirroring GiveRankCommand — closes a privilege-escalation path.

Trade integrity
- RoomTrade.clearAccepted now also resets confirmed; a stale confirmed=true
  let a user strip their side and still complete once the partner re-confirms.

Concurrency
- RoomCycleManager: iterate the synchronized bot/pet maps under their own
  monitor (lock order stays one-directional vs addBot/addPet — no deadlock).
- RoomSpecialTypes: synchronize nest/petDrink/petFood/petToy/petTree writers
  on the same monitor their getters already use.
- HabboStats: synchronize achievement-progress map accessors.
- RebugKickBallAction: drop redundant direct mutation of the shared tile-cache
  sets (updateTile invalidates them right after) — removes a data race.

Robustness
- Wired legacy parsers (HabboCount, NotHabboCount, MatchStatePosition,
  MoveRotateFurni): guard length/format so one malformed row no longer aborts
  the whole room's wired load.
- RoomLayout: fill malformed/short heightmap rows with INVALID tiles instead
  of leaving nulls, and bounds-check door coordinates.
- FurnidataWatcher: defer (instead of drop) a throttled delta so furni-name
  changes are never lost between broadcasts.
- GuildManager.getGuildMembers: fix LIMIT row-count (page size 14, not
  offset+14) so member pages no longer overlap from page 1 on.

Emulator/src/main/java/com/eu/habbo/habbohotel/guilds/GuildManager.java

@@ -423,7 +423,7 @@ public class GuildManager {
             statement.setInt(1, guild.getId());
             statement.setString(2, "%" + query + "%");
             statement.setInt(3, page * 14);
-            statement.setInt(4, (page * 14) + 14);
+            statement.setInt(4, 14);
 
             try (ResultSet set = statement.executeQuery()) {
                 while (set.next()) {

Emulator/src/main/java/com/eu/habbo/habbohotel/items/FurnidataWatcher.java

@@ -115,32 +115,39 @@ public class FurnidataWatcher {
         }
     }
 
-    private void onChange() {
+    private void onChange() throws InterruptedException {
+        // Re-index under the shared furnidata lock so the watcher and editor
+        // writes never swap the index concurrently. The lock is released before
+        // the throttle/broadcast below so a slow broadcast can't stall editor saves.
+        List<FurnidataEntry> delta;
         FurnidataLock.LOCK.lock();
         try {
             Path source = this.provider.getSource();
             if (source == null) return;
-
-            List<FurnidataEntry> delta = this.provider.reindex(new FurnidataReader(source, this.maxBytes).read());
-            if (delta.isEmpty()) return;
-
-            long now = System.currentTimeMillis();
-            if (now - this.lastBroadcast < this.minIntervalMs) {
-                LOGGER.info("FurnidataWatcher: {} changes indexed but broadcast skipped (min interval) — clients update on next change or reconnect", delta.size());
-                return;
-            }
-            this.lastBroadcast = now;
-
-            FurnitureDataReloadComposer composer = (delta.size() > this.deltaCap)
-                ? new FurnitureDataReloadComposer(FurnitureDataReloadComposer.MODE_RELOAD_HINT, List.of())
-                : new FurnitureDataReloadComposer(FurnitureDataReloadComposer.MODE_DELTA, delta);
-
-            broadcast(composer);
-            LOGGER.info("FurnidataWatcher: broadcast {} ({} entries)",
-                delta.size() > this.deltaCap ? "reload-hint" : "delta", delta.size());
+            delta = this.provider.reindex(new FurnidataReader(source, this.maxBytes).read());
         } finally {
             FurnidataLock.LOCK.unlock();
         }
+        if (delta.isEmpty()) return;
+
+        // Min-interval throttle: the index has already been swapped, so we must
+        // not drop this delta (the next reindex would diff against the updated
+        // index and never re-emit it). Instead, defer the broadcast until the
+        // interval elapses. Running on a dedicated daemon thread, sleeping is
+        // safe; file events arriving meanwhile coalesce into the next cycle.
+        long sinceLast = System.currentTimeMillis() - this.lastBroadcast;
+        if (sinceLast < this.minIntervalMs) {
+            Thread.sleep(this.minIntervalMs - sinceLast);
+        }
+        this.lastBroadcast = System.currentTimeMillis();
+
+        FurnitureDataReloadComposer composer = (delta.size() > this.deltaCap)
+            ? new FurnitureDataReloadComposer(FurnitureDataReloadComposer.MODE_RELOAD_HINT, List.of())
+            : new FurnitureDataReloadComposer(FurnitureDataReloadComposer.MODE_DELTA, delta);
+
+        broadcast(composer);
+        LOGGER.info("FurnidataWatcher: broadcast {} ({} entries)",
+            delta.size() > this.deltaCap ? "reload-hint" : "delta", delta.size());
     }
 
     private void broadcast(FurnitureDataReloadComposer composer) {

Emulator/src/main/java/com/eu/habbo/habbohotel/items/interactions/wired/conditions/WiredConditionHabboCount.java

@@ -65,8 +65,14 @@ public class WiredConditionHabboCount extends InteractionWiredCondition {
         } else {
             String[] data = wiredData.split(":");
 
-            this.lowerLimit = Integer.parseInt(data[0]);
-            this.upperLimit = Integer.parseInt(data[1]);
+            if (data.length >= 2) {
+                try {
+                    this.lowerLimit = Integer.parseInt(data[0].trim());
+                    this.upperLimit = Integer.parseInt(data[1].trim());
+                } catch (NumberFormatException ignored) {
+                    // malformed legacy data — keep the constructed defaults
+                }
+            }
             this.userSource = WiredSourceUtil.SOURCE_TRIGGER;
         }
     }

Emulator/src/main/java/com/eu/habbo/habbohotel/items/interactions/wired/conditions/WiredConditionMatchStatePosition.java

@@ -263,22 +263,29 @@ public class WiredConditionMatchStatePosition extends InteractionWiredCondition
         } else {
             String[] data = wiredData.split(":");
 
-            int itemCount = Integer.parseInt(data[0]);
+            if (data.length >= 5) {
+                try {
+                    int itemCount = Integer.parseInt(data[0]);
 
-            String[] items = data[1].split(";");
+                    String[] items = data[1].split(";");
 
-            for (int i = 0; i < itemCount; i++) {
-                String[] stuff = items[i].split("-");
+                    for (int i = 0; i < itemCount && i < items.length; i++) {
+                        String[] stuff = items[i].split("-");
 
-                if (stuff.length >= 6)
-                    this.settings.add(new WiredMatchFurniSetting(Integer.parseInt(stuff[0]), stuff[1], Integer.parseInt(stuff[2]), Integer.parseInt(stuff[3]), Integer.parseInt(stuff[4]), Double.parseDouble(stuff[5])));
-                else if (stuff.length >= 5)
-                    this.settings.add(new WiredMatchFurniSetting(Integer.parseInt(stuff[0]), stuff[1], Integer.parseInt(stuff[2]), Integer.parseInt(stuff[3]), Integer.parseInt(stuff[4])));
+                        if (stuff.length >= 6)
+                            this.settings.add(new WiredMatchFurniSetting(Integer.parseInt(stuff[0]), stuff[1], Integer.parseInt(stuff[2]), Integer.parseInt(stuff[3]), Integer.parseInt(stuff[4]), Double.parseDouble(stuff[5])));
+                        else if (stuff.length >= 5)
+                            this.settings.add(new WiredMatchFurniSetting(Integer.parseInt(stuff[0]), stuff[1], Integer.parseInt(stuff[2]), Integer.parseInt(stuff[3]), Integer.parseInt(stuff[4])));
+                    }
+
+                    this.state = data[2].equals("1");
+                    this.direction = data[3].equals("1");
+                    this.position = data[4].equals("1");
+                } catch (NumberFormatException ignored) {
+                    // malformed legacy data — keep whatever was parsed plus defaults
+                }
             }
 
-            this.state = data[2].equals("1");
-            this.direction = data[3].equals("1");
-            this.position = data[4].equals("1");
             this.altitude = false;
             this.furniSource = this.settings.isEmpty() ? WiredSourceUtil.SOURCE_TRIGGER : WiredSourceUtil.SOURCE_SELECTED;
             this.quantifier = QUANTIFIER_ALL;

Emulator/src/main/java/com/eu/habbo/habbohotel/items/interactions/wired/conditions/WiredConditionNotHabboCount.java

@@ -64,8 +64,14 @@ public class WiredConditionNotHabboCount extends InteractionWiredCondition {
             this.userSource = data.userSource;
         } else {
             String[] data = wiredData.split(":");
-            this.lowerLimit = Integer.parseInt(data[0]);
-            this.upperLimit = Integer.parseInt(data[1]);
+            if (data.length >= 2) {
+                try {
+                    this.lowerLimit = Integer.parseInt(data[0].trim());
+                    this.upperLimit = Integer.parseInt(data[1].trim());
+                } catch (NumberFormatException ignored) {
+                    // malformed legacy data — keep the constructed defaults
+                }
+            }
             this.userSource = WiredSourceUtil.SOURCE_TRIGGER;
         }
     }

Emulator/src/main/java/com/eu/habbo/habbohotel/items/interactions/wired/effects/WiredEffectMoveRotateFurni.java

@@ -190,10 +190,15 @@ public class WiredEffectMoveRotateFurni extends InteractionWiredEffect implement
                 }
 
                 for (String s : data[3].split("\r")) {
-                    HabboItem item = room.getHabboItem(Integer.parseInt(s));
+                    if (s.trim().isEmpty()) continue;
+                    try {
+                        HabboItem item = room.getHabboItem(Integer.parseInt(s.trim()));
 
-                    if (item != null)
-                        this.items.add(item);
+                        if (item != null)
+                            this.items.add(item);
+                    } catch (NumberFormatException ignored) {
+                        // skip malformed furni id token
+                    }
                 }
             }
             this.furniSource = this.items.isEmpty() ? WiredSourceUtil.SOURCE_TRIGGER : WiredSourceUtil.SOURCE_SELECTED;

Emulator/src/main/java/com/eu/habbo/habbohotel/rooms/RoomCycleManager.java

@@ -300,32 +300,37 @@ public class RoomCycleManager {
             return;
         }
 
-        TIntObjectIterator<Bot> botIterator = currentBots.iterator();
-        for (int i = currentBots.size(); i-- > 0; ) {
-            try {
-                final Bot bot;
+        // currentBots is a TCollections.synchronizedMap; the iterator is not
+        // safe against concurrent put/remove from IO threads (bot place/pickup),
+        // so we must hold the map's monitor for the whole traversal.
+        synchronized (currentBots) {
+            TIntObjectIterator<Bot> botIterator = currentBots.iterator();
+            for (int i = currentBots.size(); i-- > 0; ) {
                 try {
-                    botIterator.advance();
-                    bot = botIterator.value();
-                } catch (Exception e) {
+                    final Bot bot;
+                    try {
+                        botIterator.advance();
+                        bot = botIterator.value();
+                    } catch (Exception e) {
+                        break;
+                    }
+
+                    if (!this.room.isAllowBotsWalk() && bot.getRoomUnit().isWalking()) {
+                        bot.getRoomUnit().stopWalking();
+                        updatedUnit.add(bot.getRoomUnit());
+                        continue;
+                    }
+
+                    bot.cycle(this.room.isAllowBotsWalk());
+
+                    if (this.cycleRoomUnit(bot.getRoomUnit(), RoomUnitType.BOT)) {
+                        updatedUnit.add(bot.getRoomUnit());
+                    }
+
+                } catch (NoSuchElementException e) {
+                    LOGGER.error("Caught exception", e);
                     break;
                 }
-
-                if (!this.room.isAllowBotsWalk() && bot.getRoomUnit().isWalking()) {
-                    bot.getRoomUnit().stopWalking();
-                    updatedUnit.add(bot.getRoomUnit());
-                    continue;
-                }
-
-                bot.cycle(this.room.isAllowBotsWalk());
-
-                if (this.cycleRoomUnit(bot.getRoomUnit(), RoomUnitType.BOT)) {
-                    updatedUnit.add(bot.getRoomUnit());
-                }
-
-            } catch (NoSuchElementException e) {
-                LOGGER.error("Caught exception", e);
-                break;
             }
         }
     }
@@ -339,31 +344,35 @@ public class RoomCycleManager {
             return;
         }
 
-        TIntObjectIterator<Pet> petIterator = currentPets.iterator();
-        for (int i = currentPets.size(); i-- > 0; ) {
-            try {
-                petIterator.advance();
-            } catch (NoSuchElementException e) {
-                LOGGER.error("Caught exception", e);
-                break;
-            }
+        // currentPets is a TCollections.synchronizedMap; hold its monitor for the
+        // whole traversal to stay safe against concurrent pet place/pickup.
+        synchronized (currentPets) {
+            TIntObjectIterator<Pet> petIterator = currentPets.iterator();
+            for (int i = currentPets.size(); i-- > 0; ) {
+                try {
+                    petIterator.advance();
+                } catch (NoSuchElementException e) {
+                    LOGGER.error("Caught exception", e);
+                    break;
+                }
 
-            Pet pet = petIterator.value();
-            if (this.cycleRoomUnit(pet.getRoomUnit(), RoomUnitType.PET)) {
-                updatedUnit.add(pet.getRoomUnit());
-            }
+                Pet pet = petIterator.value();
+                if (this.cycleRoomUnit(pet.getRoomUnit(), RoomUnitType.PET)) {
+                    updatedUnit.add(pet.getRoomUnit());
+                }
 
-            pet.cycle();
+                pet.cycle();
 
-            if (pet.packetUpdate) {
-                updatedUnit.add(pet.getRoomUnit());
-                pet.packetUpdate = false;
-            }
+                if (pet.packetUpdate) {
+                    updatedUnit.add(pet.getRoomUnit());
+                    pet.packetUpdate = false;
+                }
 
-            if (pet.getRoomUnit().isWalking() && pet.getRoomUnit().getPath().size() == 1
-                    && pet.getRoomUnit().hasStatus(RoomUnitStatus.GESTURE)) {
-                pet.getRoomUnit().removeStatus(RoomUnitStatus.GESTURE);
-                updatedUnit.add(pet.getRoomUnit());
+                if (pet.getRoomUnit().isWalking() && pet.getRoomUnit().getPath().size() == 1
+                        && pet.getRoomUnit().hasStatus(RoomUnitStatus.GESTURE)) {
+                    pet.getRoomUnit().removeStatus(RoomUnitStatus.GESTURE);
+                    updatedUnit.add(pet.getRoomUnit());
+                }
             }
         }
     }

Emulator/src/main/java/com/eu/habbo/habbohotel/rooms/RoomLayout.java

@@ -130,13 +130,16 @@ public class RoomLayout {
     this.roomTiles = new RoomTile[this.mapSizeX][this.mapSizeY];
 
     for (short y = 0; y < this.mapSizeY; y++) {
-      if (modelTemp[y].isEmpty() || modelTemp[y].equalsIgnoreCase("\r")) {
-        continue;
-      }
+      // A row shorter/longer than the model width (or empty) cannot be parsed
+      // per-square. Previously such tiles were left null while tileExists()
+      // still reported them present, causing NPEs in the coordinate accessors.
+      // Fill them with INVALID tiles so every in-bounds coordinate is non-null.
+      boolean validRow = !modelTemp[y].isEmpty() && modelTemp[y].length() == this.mapSizeX;
 
       for (short x = 0; x < this.mapSizeX; x++) {
-        if (modelTemp[y].length() != this.mapSizeX) {
-          break;
+        if (!validRow) {
+          this.roomTiles[x][y] = new RoomTile(x, y, (short) 0, RoomTileState.INVALID, true);
+          continue;
         }
 
         String square = modelTemp[y].substring(x, x + 1).trim().toLowerCase();
@@ -159,7 +162,9 @@ public class RoomLayout {
       }
     }
 
-    this.doorTile = this.roomTiles[this.doorX][this.doorY];
+    this.doorTile = (this.doorX >= 0 && this.doorX < this.mapSizeX && this.doorY >= 0 && this.doorY < this.mapSizeY)
+        ? this.roomTiles[this.doorX][this.doorY]
+        : null;
 
     if (this.doorTile != null) {
       this.doorTile.setAllowStack(false);

Emulator/src/main/java/com/eu/habbo/habbohotel/rooms/RoomSpecialTypes.java

@@ -156,11 +156,17 @@ public class RoomSpecialTypes {
     }
 
     public void addNest(InteractionNest item) {
-        this.nests.put(item.getId(), item); this.specialItemsById.put(item.getId(), item);
+        synchronized (this.nests) {
+            this.nests.put(item.getId(), item);
+        }
+        this.specialItemsById.put(item.getId(), item);
     }
 
     public void removeNest(InteractionNest item) {
-        this.nests.remove(item.getId()); this.specialItemsById.remove(item.getId());
+        synchronized (this.nests) {
+            this.nests.remove(item.getId());
+        }
+        this.specialItemsById.remove(item.getId());
     }
 
     public THashSet<InteractionNest> getNests() {
@@ -178,11 +184,17 @@ public class RoomSpecialTypes {
     }
 
     public void addPetDrink(InteractionPetDrink item) {
-        this.petDrinks.put(item.getId(), item); this.specialItemsById.put(item.getId(), item);
+        synchronized (this.petDrinks) {
+            this.petDrinks.put(item.getId(), item);
+        }
+        this.specialItemsById.put(item.getId(), item);
     }
 
     public void removePetDrink(InteractionPetDrink item) {
-        this.petDrinks.remove(item.getId()); this.specialItemsById.remove(item.getId());
+        synchronized (this.petDrinks) {
+            this.petDrinks.remove(item.getId());
+        }
+        this.specialItemsById.remove(item.getId());
     }
 
     public THashSet<InteractionPetDrink> getPetDrinks() {
@@ -200,11 +212,17 @@ public class RoomSpecialTypes {
     }
 
     public void addPetFood(InteractionPetFood item) {
-        this.petFoods.put(item.getId(), item); this.specialItemsById.put(item.getId(), item);
+        synchronized (this.petFoods) {
+            this.petFoods.put(item.getId(), item);
+        }
+        this.specialItemsById.put(item.getId(), item);
     }
 
     public void removePetFood(InteractionPetFood petFood) {
-        this.petFoods.remove(petFood.getId()); this.specialItemsById.remove(petFood.getId());
+        synchronized (this.petFoods) {
+            this.petFoods.remove(petFood.getId());
+        }
+        this.specialItemsById.remove(petFood.getId());
     }
 
     public THashSet<InteractionPetFood> getPetFoods() {
@@ -222,11 +240,17 @@ public class RoomSpecialTypes {
     }
 
     public void addPetToy(InteractionPetToy item) {
-        this.petToys.put(item.getId(), item); this.specialItemsById.put(item.getId(), item);
+        synchronized (this.petToys) {
+            this.petToys.put(item.getId(), item);
+        }
+        this.specialItemsById.put(item.getId(), item);
     }
 
     public void removePetToy(InteractionPetToy petToy) {
-        this.petToys.remove(petToy.getId()); this.specialItemsById.remove(petToy.getId());
+        synchronized (this.petToys) {
+            this.petToys.remove(petToy.getId());
+        }
+        this.specialItemsById.remove(petToy.getId());
     }
 
     public THashSet<InteractionPetToy> getPetToys() {
@@ -244,11 +268,17 @@ public class RoomSpecialTypes {
     }
 
     public void addPetTree(InteractionPetTree item) {
-        this.petTrees.put(item.getId(), item); this.specialItemsById.put(item.getId(), item);
+        synchronized (this.petTrees) {
+            this.petTrees.put(item.getId(), item);
+        }
+        this.specialItemsById.put(item.getId(), item);
     }
 
     public void removePetTree(InteractionPetTree petTree) {
-        this.petTrees.remove(petTree.getId()); this.specialItemsById.remove(petTree.getId());
+        synchronized (this.petTrees) {
+            this.petTrees.remove(petTree.getId());
+        }
+        this.specialItemsById.remove(petTree.getId());
     }
 
     public THashSet<InteractionPetTree> getPetTrees() {

Emulator/src/main/java/com/eu/habbo/habbohotel/rooms/RoomTrade.java

@@ -264,6 +264,10 @@ public class RoomTrade {
     protected void clearAccepted() {
         for (RoomTradeUser user : this.users) {
             user.setAccepted(false);
+            // Any change to the offered items invalidates a prior confirmation;
+            // without this a stale confirmed=true lets a user strip their side
+            // and still complete the trade once the partner re-confirms.
+            user.setConfirmed(false);
         }
     }
 

Emulator/src/main/java/com/eu/habbo/habbohotel/rooms/RoomTradeUser.java

@@ -51,6 +51,10 @@ public class RoomTradeUser {
         this.confirmed = true;
     }
 
+    public void setConfirmed(boolean value) {
+        this.confirmed = value;
+    }
+
     public void addItem(HabboItem item) {
         this.items.add(item);
     }

Emulator/src/main/java/com/eu/habbo/habbohotel/users/HabboStats.java

@@ -448,14 +448,16 @@ public class HabboStats implements Runnable {
             return 0;
         }
 
-        if (this.achievementProgress.containsKey(achievement))
-            return this.achievementProgress.get(achievement);
-
-        return -1;
+        synchronized (this.achievementProgress) {
+            Integer progress = this.achievementProgress.get(achievement);
+            return progress != null ? progress : -1;
+        }
     }
 
     public void setProgress(Achievement achievement, int progress) {
-        this.achievementProgress.put(achievement, progress);
+        synchronized (this.achievementProgress) {
+            this.achievementProgress.put(achievement, progress);
+        }
     }
 
     public int getRentedTimeEnd() {

Emulator/src/main/java/com/eu/habbo/messages/incoming/housekeeping/HousekeepingSetUserRankEvent.java

@@ -11,6 +11,7 @@ import com.eu.habbo.messages.outgoing.users.UserPermissionsComposer;
 
 import java.sql.Connection;
 import java.sql.PreparedStatement;
+import java.sql.ResultSet;
 import java.sql.SQLException;
 
 public class HousekeepingSetUserRankEvent extends MessageHandler {
@@ -44,6 +45,43 @@ public class HousekeepingSetUserRankEvent extends MessageHandler {
 
         Rank rank = permissions.getRank(rankId);
 
+        // Rank-ceiling guard: an operator must never be able to grant a rank
+        // above their own, nor modify a user who already outranks them. This
+        // mirrors GiveRankCommand and prevents privilege escalation through
+        // the housekeeping path (including self-promotion).
+        int operatorRankId = this.client.getHabbo().getHabboInfo().getRank().getId();
+
+        if (rank.getId() > operatorRankId) {
+            this.client.sendResponse(new HousekeepingActionResultComposer(ACTION_KEY, false, 0, "housekeeping.error.rank_too_high"));
+            return;
+        }
+
+        Habbo online = Emulator.getGameEnvironment().getHabboManager().getHabbo(userId);
+
+        int targetRankId;
+        if (online != null) {
+            targetRankId = online.getHabboInfo().getRank().getId();
+        } else {
+            targetRankId = 0;
+            try (Connection connection = Emulator.getDatabase().getDataSource().getConnection();
+                 PreparedStatement statement = connection.prepareStatement("SELECT rank FROM users WHERE id = ? LIMIT 1")) {
+                statement.setInt(1, userId);
+                try (ResultSet set = statement.executeQuery()) {
+                    if (set.next()) {
+                        targetRankId = set.getInt("rank");
+                    }
+                }
+            } catch (SQLException e) {
+                this.client.sendResponse(new HousekeepingActionResultComposer(ACTION_KEY, false, 0, "housekeeping.error.db_failed"));
+                return;
+            }
+        }
+
+        if (targetRankId > operatorRankId) {
+            this.client.sendResponse(new HousekeepingActionResultComposer(ACTION_KEY, false, 0, "housekeeping.error.rank_too_high"));
+            return;
+        }
+
         // Persist for the offline path. Online users get their in-memory
         // HabboInfo.rank rebound below so server-side hasPermission()
         // checks land on the new permission set without a relogin.
@@ -57,8 +95,6 @@ public class HousekeepingSetUserRankEvent extends MessageHandler {
             return;
         }
 
-        Habbo online = Emulator.getGameEnvironment().getHabboManager().getHabbo(userId);
-
         if (online != null) {
             online.getHabboInfo().setRank(rank);
             // Ship the refreshed permissions snapshot — same payload the

Emulator/src/main/java/com/eu/habbo/threading/runnables/RebugKickBallAction.java

@@ -165,12 +165,10 @@ public class RebugKickBallAction implements Runnable {
                 this.dead = true;
             }
 
-            THashSet<HabboItem> oldItems = this.room.getItemsAt(oldTile);
-            if (oldItems != null && !oldItems.isEmpty()) {
-                oldItems.remove(this.ball);
-            }
-            this.room.getItemsAt(nextTile).add(this.ball);
-
+            // updateTile() below removes both tiles from the item cache (rebuilt
+            // lazily from the ball's already-updated position), so mutating the
+            // shared cached THashSets here is both redundant and a data race
+            // against the room-cycle/IO threads iterating those same sets.
             this.room.updateTile(oldTile);
             this.room.updateTile(nextTile);