refactor: extract findOnUseSpellId helper, add warden hash comment

- spell_handler: extract duplicated item on-use spell lookup into
  findOnUseSpellId() — was copy-pasted in useItemBySlot and useItemInBag
- warden_handler: add why-comment explaining the door model HMAC-SHA1
  hash table (wall-hack detection for unmodified 3.3.5a client data)

include/game/spell_handler.hpp

@@ -249,6 +249,9 @@ private:
     void handleChannelUpdate(network::Packet& packet);
 
     // --- Internal helpers ---
+    // Find the on-use spell for an item (trigger=0 Use or trigger=5 NoDelay).
+    // CMSG_USE_ITEM requires a valid spellId or the server silently ignores it.
+    uint32_t findOnUseSpellId(uint32_t itemId) const;
     void loadSpellNameCache() const;
     void loadSkillLineAbilityDbc();
     void categorizeTrainerSpells();

src/game/spell_handler.cpp

@@ -446,6 +446,18 @@ void SpellHandler::confirmPetUnlearn() {
     petUnlearnCost_ = 0;
 }
 
+uint32_t SpellHandler::findOnUseSpellId(uint32_t itemId) const {
+    if (auto* info = owner_.getItemInfo(itemId)) {
+        for (const auto& sp : info->spells) {
+            // spellTrigger 0 = "Use", 5 = "No Delay" — both are player-activated on-use effects
+            if (sp.spellId != 0 && (sp.spellTrigger == 0 || sp.spellTrigger == 5)) {
+                return sp.spellId;
+            }
+        }
+    }
+    return 0;
+}
+
 void SpellHandler::useItemBySlot(int backpackIndex) {
     if (backpackIndex < 0 || backpackIndex >= owner_.inventory.getBackpackSize()) return;
     const auto& slot = owner_.inventory.getBackpackSlot(backpackIndex);
@@ -457,16 +469,7 @@ void SpellHandler::useItemBySlot(int backpackIndex) {
     }
 
     if (itemGuid != 0 && owner_.state == WorldState::IN_WORLD && owner_.socket) {
-        uint32_t useSpellId = 0;
+        uint32_t useSpellId = findOnUseSpellId(slot.item.itemId);
-        if (auto* info = owner_.getItemInfo(slot.item.itemId)) {
-            for (const auto& sp : info->spells) {
-                if (sp.spellId != 0 && (sp.spellTrigger == 0 || sp.spellTrigger == 5)) {
-                    useSpellId = sp.spellId;
-                    break;
-                }
-            }
-        }
-
         auto packet = owner_.packetParsers_
             ? owner_.packetParsers_->buildUseItem(0xFF, static_cast<uint8_t>(23 + backpackIndex), itemGuid, useSpellId)
             : UseItemPacket::build(0xFF, static_cast<uint8_t>(23 + backpackIndex), itemGuid, useSpellId);
@@ -498,16 +501,7 @@ void SpellHandler::useItemInBag(int bagIndex, int slotIndex) {
              " itemGuid=0x", std::hex, itemGuid, std::dec);
 
     if (itemGuid != 0 && owner_.state == WorldState::IN_WORLD && owner_.socket) {
-        uint32_t useSpellId = 0;
+        uint32_t useSpellId = findOnUseSpellId(slot.item.itemId);
-        if (auto* info = owner_.getItemInfo(slot.item.itemId)) {
-            for (const auto& sp : info->spells) {
-                if (sp.spellId != 0 && (sp.spellTrigger == 0 || sp.spellTrigger == 5)) {
-                    useSpellId = sp.spellId;
-                    break;
-                }
-            }
-        }
-
         uint8_t wowBag = static_cast<uint8_t>(19 + bagIndex);
         auto packet = owner_.packetParsers_
             ? owner_.packetParsers_->buildUseItem(wowBag, static_cast<uint8_t>(slotIndex), itemGuid, useSpellId)

src/game/warden_handler.cpp

@@ -116,6 +116,9 @@ bool hmacSha1Matches(const uint8_t seedBytes[4], const std::string& text, const
     return outLen == SHA_DIGEST_LENGTH && std::memcmp(out, expected, SHA_DIGEST_LENGTH) == 0;
 }
 
+// Pre-computed HMAC-SHA1 hashes of known door M2 models that Warden checks
+// to verify the client hasn't modified collision geometry (wall-hack detection).
+// These hashes match the unmodified 3.3.5a client data files.
 const std::unordered_map<std::string, std::array<uint8_t, 20>>& knownDoorHashes() {
     static const std::unordered_map<std::string, std::array<uint8_t, 20>> k = {
         {"world\\lordaeron\\stratholme\\activedoodads\\doors\\nox_door_plague.m2",