fix(Core/Battlefield): block invites and kicks from BF raids (#26015)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/server/game/Entities/Player/Player.cpp

@@ -13108,6 +13108,11 @@ PartyResult Player::CanUninviteFromGroup(ObjectGuid targetPlayerGUID) const
 
         if (InBattleground())
             return ERR_INVITE_RESTRICTED;
+
+        // BF raids are owned by the Battlefield system; leaders/assistants must not
+        // be able to kick members (would drop their team assignment mid-battle).
+        if (grp->isBFGroup())
+            return ERR_NOT_LEADER;
     }
 
     return ERR_PARTY_RESULT_OK;

src/server/game/Handlers/GroupHandler.cpp

@@ -126,6 +126,16 @@ void WorldSession::HandleGroupInviteOpcode(WorldPacket& recvData)
         return;
     }
 
+    // Battlefield raids (e.g. Wintergrasp) have their composition managed by the BF
+    // system based on queue and team balance. Letting raid members recruit outsiders
+    // bypasses Battlefield::AddOrSetPlayerToCorrectBfGroup, which on WG entry then
+    // refuses to add the invitee because they are already in a BF group.
+    if (Group* invitingGroup = invitingPlayer->GetGroup(); invitingGroup && invitingGroup->isBFGroup())
+    {
+        SendPartyResult(PARTY_OP_INVITE, membername, ERR_NOT_LEADER);
+        return;
+    }
+
     Group* group = invitingPlayer->GetGroup();
     if (group && group->isBGGroup())
         group = invitingPlayer->GetOriginalGroup();