refactor: replace magic slot offset 23 with NUM_EQUIP_SLOTS, simplify channel search

- Replace all 11 occurrences of magic number 23 in backpack slot
  calculations with Inventory::NUM_EQUIP_SLOTS across inventory_handler,
  spell_handler, and inventory.cpp
- Add why-comment to NUM_EQUIP_SLOTS explaining WoW slot layout
  (equipment 0-22, backpack starts at 23 in bag 0xFF)
- Add why-comment on 0x80000000 bit mask in item query response
  (high bit flags negative/missing entry response)
- Replace manual channel membership loops with std::find in
  chat_handler.cpp (YOU_JOINED and PLAYER_ALREADY_MEMBER cases)
- Add why-comment on PLAYER_ALREADY_MEMBER reconnect edge case

include/game/inventory.hpp

@@ -70,6 +70,8 @@ class Inventory {
 public:
     static constexpr int BACKPACK_SLOTS = 16;
     static constexpr int KEYRING_SLOTS = 32;
+    // WoW slot layout: 0-22 are equipment (head, neck, ... tabard, mainhand, offhand, ranged, ammo).
+    // Backpack inventory starts at slot 23 in bag 0xFF, so packet slot = NUM_EQUIP_SLOTS + backpackIndex.
     static constexpr int NUM_EQUIP_SLOTS = 23;
     static constexpr int NUM_BAG_SLOTS = 4;
     static constexpr int MAX_BAG_SIZE = 36;

src/game/chat_handler.cpp

@@ -435,11 +435,7 @@ void ChatHandler::handleChannelNotify(network::Packet& packet) {
 
     switch (data.notifyType) {
         case ChannelNotifyType::YOU_JOINED: {
-            bool found = false;
+            if (std::find(joinedChannels_.begin(), joinedChannels_.end(), data.channelName) == joinedChannels_.end()) {
-            for (const auto& ch : joinedChannels_) {
-                if (ch == data.channelName) { found = true; break; }
-            }
-            if (!found) {
                 joinedChannels_.push_back(data.channelName);
             }
             MessageChatData msg;
@@ -461,11 +457,9 @@ void ChatHandler::handleChannelNotify(network::Packet& packet) {
             break;
         }
         case ChannelNotifyType::PLAYER_ALREADY_MEMBER: {
-            bool found = false;
+            // Server confirms we're in this channel but our local list doesn't have it yet —
-            for (const auto& ch : joinedChannels_) {
+            // can happen after reconnect or if the join notification was missed.
-                if (ch == data.channelName) { found = true; break; }
+            if (std::find(joinedChannels_.begin(), joinedChannels_.end(), data.channelName) == joinedChannels_.end()) {
-            }
-            if (!found) {
                 joinedChannels_.push_back(data.channelName);
                 LOG_INFO("Already in channel: ", data.channelName);
             }

src/game/inventory.cpp

@@ -239,7 +239,7 @@ std::vector<Inventory::SwapOp> Inventory::computeSortSwaps() const {
     entries.reserve(BACKPACK_SLOTS + NUM_BAG_SLOTS * MAX_BAG_SIZE);
 
     for (int i = 0; i < BACKPACK_SLOTS; ++i) {
-        entries.push_back({0xFF, static_cast<uint8_t>(23 + i),
+        entries.push_back({0xFF, static_cast<uint8_t>(NUM_EQUIP_SLOTS + i),
                            backpack[i].item.itemId, backpack[i].item.quality,
                            backpack[i].item.stackCount});
     }

src/game/inventory_handler.cpp

@@ -1047,7 +1047,7 @@ void InventoryHandler::autoEquipItemBySlot(int backpackIndex) {
     if (slot.empty()) return;
 
     if (owner_.state == WorldState::IN_WORLD && owner_.socket) {
-        auto packet = AutoEquipItemPacket::build(0xFF, static_cast<uint8_t>(23 + backpackIndex));
+        auto packet = AutoEquipItemPacket::build(0xFF, static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + backpackIndex));
         owner_.socket->send(packet);
     }
 }
@@ -1087,8 +1087,8 @@ void InventoryHandler::useItemBySlot(int backpackIndex) {
                         " spellId=", useSpellId, " spellCount=", info->spells.size());
         }
         auto packet = owner_.packetParsers_
-            ? owner_.packetParsers_->buildUseItem(0xFF, static_cast<uint8_t>(23 + backpackIndex), itemGuid, useSpellId)
+            ? owner_.packetParsers_->buildUseItem(0xFF, static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + backpackIndex), itemGuid, useSpellId)
-            : UseItemPacket::build(0xFF, static_cast<uint8_t>(23 + backpackIndex), itemGuid, useSpellId);
+            : UseItemPacket::build(0xFF, static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + backpackIndex), itemGuid, useSpellId);
         owner_.socket->send(packet);
     } else if (itemGuid == 0) {
         LOG_WARNING("useItemBySlot: itemGuid=0 for item='", slot.item.name,
@@ -1145,8 +1145,8 @@ void InventoryHandler::openItemBySlot(int backpackIndex) {
     if (backpackIndex < 0 || backpackIndex >= owner_.inventory.getBackpackSize()) return;
     if (owner_.inventory.getBackpackSlot(backpackIndex).empty()) return;
     if (owner_.state != WorldState::IN_WORLD || !owner_.socket) return;
-    auto packet = OpenItemPacket::build(0xFF, static_cast<uint8_t>(23 + backpackIndex));
+    auto packet = OpenItemPacket::build(0xFF, static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + backpackIndex));
-    LOG_INFO("openItemBySlot: CMSG_OPEN_ITEM bag=0xFF slot=", (23 + backpackIndex));
+    LOG_INFO("openItemBySlot: CMSG_OPEN_ITEM bag=0xFF slot=", (Inventory::NUM_EQUIP_SLOTS + backpackIndex));
     owner_.socket->send(packet);
 }
 
@@ -1181,7 +1181,7 @@ void InventoryHandler::splitItem(uint8_t srcBag, uint8_t srcSlot, uint8_t count)
     int freeBp = owner_.inventory.findFreeBackpackSlot();
     if (freeBp >= 0) {
         uint8_t dstBag = 0xFF;
-        uint8_t dstSlot = static_cast<uint8_t>(23 + freeBp);
+        uint8_t dstSlot = static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + freeBp);
         LOG_INFO("splitItem: src(bag=", (int)srcBag, " slot=", (int)srcSlot,
                  ") count=", (int)count, " -> dst(bag=0xFF slot=", (int)dstSlot, ")");
         auto packet = SplitItemPacket::build(srcBag, srcSlot, dstBag, dstSlot, count);
@@ -1248,7 +1248,7 @@ void InventoryHandler::unequipToBackpack(EquipSlot equipSlot) {
     uint8_t srcBag = 0xFF;
     uint8_t srcSlot = static_cast<uint8_t>(equipSlot);
     uint8_t dstBag = 0xFF;
-    uint8_t dstSlot = static_cast<uint8_t>(23 + freeSlot);
+    uint8_t dstSlot = static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + freeSlot);
 
     LOG_INFO("UnequipToBackpack: equipSlot=", (int)srcSlot,
              " -> backpackIndex=", freeSlot, " (dstSlot=", (int)dstSlot, ")");
@@ -1538,7 +1538,7 @@ bool InventoryHandler::attachItemFromBackpack(int backpackIndex) {
             mailAttachments_[i].itemGuid = itemGuid;
             mailAttachments_[i].item = slot.item;
             mailAttachments_[i].srcBag = 0xFF;
-            mailAttachments_[i].srcSlot = static_cast<uint8_t>(23 + backpackIndex);
+            mailAttachments_[i].srcSlot = static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + backpackIndex);
             return true;
         }
     }
@@ -1730,7 +1730,7 @@ void InventoryHandler::withdrawItem(uint8_t srcBag, uint8_t srcSlot) {
         owner_.addSystemChatMessage("Inventory is full.");
         return;
     }
-    uint8_t dstSlot = static_cast<uint8_t>(23 + freeSlot);
+    uint8_t dstSlot = static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + freeSlot);
     auto packet = SwapItemPacket::build(0xFF, dstSlot, srcBag, srcSlot);
     owner_.socket->send(packet);
 }
@@ -2225,7 +2225,7 @@ void InventoryHandler::useEquipmentSet(uint32_t setId) {
             for (int bp = 0; bp < 16 && !found; ++bp) {
                 if (owner_.getBackpackItemGuid(bp) == itemGuid) {
                     srcBag = 0xFF;
-                    srcSlot = static_cast<uint8_t>(23 + bp);
+                    srcSlot = static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + bp);
                     found = true;
                 }
             }
@@ -2355,6 +2355,8 @@ void InventoryHandler::handleItemQueryResponse(network::Packet& packet) {
         // Without this, the entry stays in pendingItemQueries_ forever, blocking retries.
         if (packet.getSize() >= 4) {
             packet.setReadPos(0);
+            // High bit indicates a negative (invalid/missing) item entry response;
+            // mask it off so we can still clear the pending query by entry ID.
             uint32_t rawEntry = packet.readUInt32() & ~0x80000000u;
             owner_.pendingItemQueries_.erase(rawEntry);
         }

src/game/spell_handler.cpp

@@ -471,8 +471,8 @@ void SpellHandler::useItemBySlot(int backpackIndex) {
     if (itemGuid != 0 && owner_.state == WorldState::IN_WORLD && owner_.socket) {
         uint32_t useSpellId = findOnUseSpellId(slot.item.itemId);
         auto packet = owner_.packetParsers_
-            ? owner_.packetParsers_->buildUseItem(0xFF, static_cast<uint8_t>(23 + backpackIndex), itemGuid, useSpellId)
+            ? owner_.packetParsers_->buildUseItem(0xFF, static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + backpackIndex), itemGuid, useSpellId)
-            : UseItemPacket::build(0xFF, static_cast<uint8_t>(23 + backpackIndex), itemGuid, useSpellId);
+            : UseItemPacket::build(0xFF, static_cast<uint8_t>(Inventory::NUM_EQUIP_SLOTS + backpackIndex), itemGuid, useSpellId);
         owner_.socket->send(packet);
     } else if (itemGuid == 0) {
         owner_.addSystemChatMessage("Cannot use that item right now.");