fix(Core/Battlegrounds): fix invited-count accounting on BG entry (#26556)

src/server/game/Handlers/BattleGroundHandler.cpp

@@ -544,7 +544,31 @@ void WorldSession::HandleBattleFieldPortOpcode(WorldPacket& recvData)
         sLFGMgr->LeaveAllLfgQueues(_player->GetGUID(), false);
 
         _player->SetBattlegroundId(bg->GetInstanceID(), bg->GetBgTypeID(), queueSlot, true, bgTypeId == BATTLEGROUND_RB, teamId);
-        sBattlegroundMgr->SendToBattleground(_player, ginfo.IsInvitedToBGInstanceGUID, bgTypeId);
+
+        if (!sBattlegroundMgr->SendToBattleground(_player, ginfo.IsInvitedToBGInstanceGUID, bgTypeId))
+        {
+            // The teleport never started (instance gone, or a synchronous
+            // TeleportTo veto such as a DK still locked to Ebon Hold). The accept
+            // already pulled the player out of the queue and he can't decline
+            // now, so undo the accept here -- otherwise the invited reservation
+            // leaks forever, permanently skewing team selection and blocking the
+            // empty instance's cleanup.
+            bg->DecreaseInvitedCount(teamId);
+            _player->RemoveBattlegroundQueueId(bgQueueTypeId);
+            _player->SetBattlegroundId(0, BATTLEGROUND_TYPE_NONE, PLAYER_MAX_BATTLEGROUND_QUEUES, false, false, TEAM_NEUTRAL);
+
+            sBattlegroundMgr->BuildBattlegroundStatusPacket(&data, bg, queueSlot, STATUS_NONE, 0, 0, 0, TEAM_NEUTRAL);
+            SendPacket(&data);
+
+            // Free slot -> let the queue refill it. BG only, like the sibling
+            // leave-queue path: an arena update needs its own type/rating.
+            if (!ginfo.ArenaType)
+                sBattlegroundMgr->ScheduleQueueUpdate(0, 0, bgQueueTypeId, bgTypeId, bracketEntry->GetBracketId());
+
+            LOG_ERROR("bg.battleground", "Battleground: player {} {} failed to teleport into bg {}, bgtype {}; released the invited reservation.",
+                _player->GetName(), _player->GetGUID().ToString(), bg->GetInstanceID(), bg->GetBgTypeID());
+            return;
+        }
 
         LOG_DEBUG("bg.battleground", "Battleground: player {} {} joined battle for bg {}, bgtype {}, queue type {}.", _player->GetName(), _player->GetGUID().ToString(), bg->GetInstanceID(), bg->GetBgTypeID(), bgQueueTypeId);
     }