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

src/server/game/Battlegrounds/BattlegroundMgr.cpp

@@ -647,7 +647,7 @@ void BattlegroundMgr::BuildBattlegroundListPacket(WorldPacket* data, ObjectGuid
     }
 }
 
-void BattlegroundMgr::SendToBattleground(Player* player, uint32 instanceId, BattlegroundTypeId bgTypeId)
+bool BattlegroundMgr::SendToBattleground(Player* player, uint32 instanceId, BattlegroundTypeId bgTypeId)
 {
     if (Battleground* bg = GetBattleground(instanceId, bgTypeId))
     {
@@ -655,12 +655,11 @@ void BattlegroundMgr::SendToBattleground(Player* player, uint32 instanceId, Batt
         Position const* pos = bg->GetTeamStartPosition(player->GetBgTeamId());
 
         LOG_DEBUG("bg.battleground", "BattlegroundMgr::SendToBattleground: Sending {} to map {}, {} (bgType {})", player->GetName(), mapid, pos->ToString(), bgTypeId);
-        player->TeleportTo(mapid, pos->GetPositionX(), pos->GetPositionY(), pos->GetPositionZ(), pos->GetOrientation());
-    }
-    else
-    {
-        LOG_ERROR("bg.battleground", "BattlegroundMgr::SendToBattleground: Instance {} (bgType {}) not found while trying to teleport player {}", instanceId, bgTypeId, player->GetName());
+        return player->TeleportTo(mapid, pos->GetPositionX(), pos->GetPositionY(), pos->GetPositionZ(), pos->GetOrientation());
     }
+
+    LOG_ERROR("bg.battleground", "BattlegroundMgr::SendToBattleground: Instance {} (bgType {}) not found while trying to teleport player {}", instanceId, bgTypeId, player->GetName());
+    return false;
 }
 
 void BattlegroundMgr::SendAreaSpiritHealerQueryOpcode(Player* player, Battleground* bg, ObjectGuid guid)

src/server/game/Battlegrounds/BattlegroundMgr.h

@@ -93,7 +93,10 @@ public:
     void LoadBattlegroundTemplates();
     void DeleteAllBattlegrounds();
 
-    void SendToBattleground(Player* player, uint32 InstanceID, BattlegroundTypeId bgTypeId);
+    // Returns false when the teleport could not start (instance gone, or a
+    // synchronous TeleportTo failure) so the accept path can release the
+    // otherwise-orphaned invited reservation.
+    bool SendToBattleground(Player* player, uint32 InstanceID, BattlegroundTypeId bgTypeId);
 
     /* Battleground queues */
     BattlegroundQueue& GetBattlegroundQueue(BattlegroundQueueTypeId bgQueueTypeId) { return m_BattlegroundQueues[bgQueueTypeId]; }

src/server/game/Battlegrounds/BattlegroundQueue.cpp

@@ -1302,13 +1302,16 @@ int32 BattlegroundQueue::GetQueueAnnouncementTimer(uint32 bracketId) const
 
 void BattlegroundQueue::InviteGroupToBG(GroupQueueInfo* ginfo, Battleground* bg, TeamId teamId)
 {
+    // An already-invited group keeps the side it was invited under: writing
+    // teamId here would split a future re-invite's IncreaseInvitedCount from the
+    // original side's DecreaseInvitedCount at leave, desyncing the ledger.
+    if (ginfo->IsInvitedToBGInstanceGUID)
+        return;
+
     // set side if needed
     if (teamId != TEAM_NEUTRAL)
         ginfo->teamId = teamId;
 
-    if (ginfo->IsInvitedToBGInstanceGUID)
-        return;
-
     // set invitation
     ginfo->IsInvitedToBGInstanceGUID = bg->GetInstanceID();
 

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);
     }

src/server/scripts/Commands/cs_misc.cpp

@@ -499,8 +499,21 @@ public:
             // Remove from LFG queues
             sLFGMgr->LeaveAllLfgQueues(player->GetGUID(), false);
 
+            // Book the reservation like the queue path does, so it is symmetric
+            // with RemovePlayerAtLeave's decrement and the 0-players/0-invited
+            // state can't let Battleground::Update delete the arena while players
+            // are still on the loading screen.
+            bg->IncreaseInvitedCount(teamId);
             player->SetBattlegroundId(bg->GetInstanceID(), bgTypeId, queueSlot, true, false, teamId);
-            sBattlegroundMgr->SendToBattleground(player, bg->GetInstanceID(), bgTypeId);
+
+            // A synchronous teleport failure would strand that reservation (the
+            // player never enters and never reaches RemovePlayerAtLeave), leaving
+            // the arena undeletable; release it and reset his bg data.
+            if (!sBattlegroundMgr->SendToBattleground(player, bg->GetInstanceID(), bgTypeId))
+            {
+                bg->DecreaseInvitedCount(teamId);
+                player->SetBattlegroundId(0, BATTLEGROUND_TYPE_NONE, PLAYER_MAX_BATTLEGROUND_QUEUES, false, false, TEAM_NEUTRAL);
+            }
         }
 
         handler->PSendSysMessage("Success! Players are now being teleported to the arena.");