GetInventoryItemsForSlot: filter by player proficiency

Mail helms were showing up for cloth classes — the function only
checked invType→slot shape, not whether the player could actually
equip the item.

Adds a proficiency gate using the engine's per-itemClass mask table
at [0x00C4D4A0], populated by the SMSG_SET_PROFICIENCY handler at
0x005E7B70. `table[itemClass] & (1 << subclass)` is the same lookup
4.3.4's Script_GetInventoryItemsForSlot does (via FUN_00553AD0 ->
DAT_00DD4D38), and the same source the engine's own tooltip red-text
coloring and cursor-drop equip check read from. Covers both armor
and weapon proficiencies in one mask lookup.

README.md

@@ -35,7 +35,7 @@ Full per-function reference: **[docs/API.md](docs/API.md)**.
 | [Gossip](docs/API.md#gossip) | `C_GossipInfo.CloseGossip`, `C_GossipInfo.GetActiveQuests`, `C_GossipInfo.GetAvailableQuests`, `C_GossipInfo.GetNumActiveQuests`, `C_GossipInfo.GetNumAvailableQuests`, `C_GossipInfo.GetNumOptions`, `C_GossipInfo.GetOptions`, `C_GossipInfo.GetText`, `C_GossipInfo.SelectActiveQuest`, `C_GossipInfo.SelectAvailableQuest`, `C_GossipInfo.SelectOption`, `C_GossipInfo.SelectOptionByIndex` |
 | [GameTooltip](docs/API.md#gametooltip) | `GameTooltip:GetGameObject`, `GameTooltip:GetItem`, `GameTooltip:GetOwner`, `GameTooltip:GetSpell`, `GameTooltip:GetUnitGUID`, `GameTooltip:HasGameObject`, `GameTooltip:HasItem`, `GameTooltip:HasSpell`, `GameTooltip:HasUnit`, `GameTooltip:SetEquipmentSet`, `GameTooltip:SetInventoryItemByID`, `GameTooltip:SetItemByGUID`, `GameTooltip:SetItemByID`, `GameTooltip:SetSpellByID`, `GameTooltip:SetTalentByID`, `GameTooltip:SetUnitAura` |
 | [Hooks](docs/API.md#hooks) | `hooksecurefunc` |
-| [Input](docs/API.md#input) | `IsLeftAltKeyDown`, `IsLeftControlKeyDown`, `IsLeftShiftKeyDown`, `IsModifierKeyDown`, `IsRightAltKeyDown`, `IsRightControlKeyDown`, `IsRightShiftKeyDown` |
+| [Input](docs/API.md#input) | `IsLeftAltKeyDown`, `IsLeftControlKeyDown`, `IsLeftShiftKeyDown`, `IsModifierKeyDown`, `IsMouseButtonDown`, `IsRightAltKeyDown`, `IsRightControlKeyDown`, `IsRightShiftKeyDown` |
 | [Instance](docs/API.md#instance) | `GetInstanceInfo` |
 | [Item](docs/API.md#item) | `C_Item.DoesItemExist`, `C_Item.DoesItemExistByID`, `C_Item.EquipItemByName`, `C_Item.GetCurrentItemLevel`, `C_Item.GetDetailedItemLevelInfo`, `C_Item.GetItemCount`, `C_Item.GetItemFamily`, `C_Item.GetItemGUID`, `C_Item.GetItemIcon`, `C_Item.GetItemIconByID`, `C_Item.GetItemID`, `C_Item.GetItemInfoInstant`, `C_Item.GetItemInventoryType`, `C_Item.GetItemInventoryTypeByID`, `C_Item.GetItemLink`, `C_Item.GetItemLocation`, `C_Item.GetItemMaxStackSize`, `C_Item.GetItemMaxStackSizeByID`, `C_Item.GetItemName`, `C_Item.GetItemNameByID`, `C_Item.GetItemQuality`, `C_Item.GetItemQualityByID`, `C_Item.GetItemSellPrice`, `C_Item.GetItemSellPriceByID`, `C_Item.GetItemSetID`, `C_Item.GetItemSetIDByID`, `C_Item.GetItemSetInfo`, `C_Item.GetItemSpell`, `C_Item.GetItemUniqueness`, `C_Item.GetItemUniquenessByID`, `C_Item.GetStackCount`, `C_Item.GetWeaponEnchantInfo`, `C_Item.IsBound`, `C_Item.IsEquippableItem`, `C_Item.IsEquippedItem`, `C_Item.IsItemDataCached`, `C_Item.IsItemDataCachedByID`, `C_Item.IsItemOpenable`, `C_Item.IsLocked`, `C_Item.LockItem`, `C_Item.LockItemByGUID`, `C_Item.UnlockAllItems`, `C_Item.UnlockItem`, `C_Item.RequestLoadItemData`, `C_Item.RequestLoadItemDataByID`, `C_Item.UseItemByName`, `GetAuctionItemID`, `GetAuctionSellItemID`, `GetAverageItemLevel`, `GetCraftReagentItemID`, `GetInboxItemID`, `GetInventoryItemDurability`, `GetInventoryItemID`, `GetInventoryItemsForSlot`, `GetInventoryItemRepairCost`, `GetItemIcon`, `GetLootRollItemID`, `GetLootSlotItemID`, `GetMerchantItemID`, `GetQuestItemID`, `GetQuestLogItemID`, `GetTradePlayerItemID`, `GetTradeSkillItemID`, `GetTradeSkillReagentItemID`, `GetTradeTargetItemID`, `OffhandHasWeapon` |
 | [Macros](docs/API.md#macros) | `GetLooseMacroIcons`, `GetLooseMacroItemIcons`, `GetMacroIcons`, `GetMacroItemIcons`, `GetMacroSpell` |

docs/API.md

@@ -152,6 +152,7 @@ build instructions.
   - [`IsLeftControlKeyDown()` / `IsRightControlKeyDown()`](#isleftcontrolkeydown--isrightcontrolkeydown)
   - [`IsLeftAltKeyDown()` / `IsRightAltKeyDown()`](#isleftaltkeydown--isrightaltkeydown)
   - [`IsModifierKeyDown()`](#ismodifierkeydown)
+  - [`IsMouseButtonDown([button])`](#ismousebuttondownbutton)
 
 - [Instance](#instance)
   - [`GetInstanceInfo()`](#getinstanceinfo)
@@ -3337,6 +3338,41 @@ otherwise. Equivalent to
 `IsShiftKeyDown() or IsControlKeyDown() or IsAltKeyDown()` but in one
 call.
 
+### `IsMouseButtonDown([button])`
+
+Returns `true` if the given mouse button is currently held, `false`
+otherwise. With no argument (or `nil`), returns `true` if **any**
+mouse button is held.
+
+`button` is either a 1-based ID or a name string:
+
+| ID  | Name |
+|-----|------|
+| `1` | `"LeftButton"` |
+| `2` | `"RightButton"` |
+| `3` | `"MiddleButton"` |
+| `4` | `"Button4"` (XBUTTON1 / first side button) |
+| `5` | `"Button5"` (XBUTTON2 / second side button) |
+
+Unrecognized IDs / names return `false` (matches modern semantics:
+the named button just isn't held — bad input doesn't fall through
+to the any-button check).
+
+State is maintained from the same `WH_GETMESSAGE` hook that drives
+`GLOBAL_MOUSE_DOWN` / `GLOBAL_MOUSE_UP`, so press/release transitions
+register at exactly the moment the corresponding event fires. Hook
+scopes to WoW's message queue — clicks made while the game is
+alt-tabbed out don't deliver, which means the state can stay
+"down" if a button was held while focus left the window. Most uses
+of `IsMouseButtonDown` are gated behind a frame that just received
+mouse focus, so this rarely matters in practice.
+
+```lua
+if IsMouseButtonDown("RightButton") then
+    -- right-button-held bindings
+end
+```
+
 ## Instance
 
 ### `GetInstanceInfo()`

src/Offsets.h

@@ -1488,6 +1488,35 @@ enum Offsets {
     VAR_SKILL_LINE_COUNT = 0x00C0D930,
     OFF_SKILL_LINE_NAME = 0x0C,
 
+    // Player's known-skills table — separate from the DBC. Populated
+    // by the engine on login from server data; entries are pointers
+    // to per-skill records. Each record's `+0x00` is the
+    // `SkillLine.dbc` row (or `0` for header / category rows), and
+    // `+0x10` is the current skill rank (other rank/modifier fields
+    // follow). Source: `Script_GetSkillLineInfo` at `0x004D3610`,
+    // which walks this array indexed by the Lua arg.
+    VAR_PLAYER_SKILL_LIST = 0x00B7318C,
+    VAR_PLAYER_SKILL_COUNT = 0x00B731B8,
+    OFF_PLAYER_SKILL_LINE_ID = 0x00,
+    OFF_PLAYER_SKILL_RANK = 0x10,
+
+    // Per-itemClass proficiency bitmap maintained by the engine.
+    // 17 u32 entries (indexed by Item.dbc `m_class`, 0..16). Each
+    // entry is a bitmask where bit N is set if the player has
+    // proficiency in subclass N of that item class — i.e.
+    // `table[4] & (1 << 3)` = "can wear Mail" (armor=class 4,
+    // mail=subclass 3).
+    //
+    // Populated by SMSG_SET_PROFICIENCY's handler at
+    // `FUN_005E7B70`, which writes `table[itemClass] = mask`
+    // verbatim from the packet. Same source the engine itself uses
+    // for equip eligibility (the tooltip "Mail" red-text logic
+    // and the cursor-drop-on-paperdoll check both read this). Note:
+    // covers **weapons too** (class 2), making it strictly more
+    // general than walking the per-skill-line table for individual
+    // armor proficiencies.
+    VAR_PROFICIENCY_TABLE = 0x00C4D4A0,
+
     // Spell.dbc `BaseLevel` — the level a spell becomes available
     // (trainer offers it, quest reward grants it, etc.). Distinct
     // from `SpellLevel` at +0x74 which is the effective level used

src/addons/Info.cpp

@@ -115,13 +115,24 @@ int PushFieldOrNil(void *L, FieldByName_t accessor) {
 // `C_AddOns.GetAddOnName(indexOrName)` — the addon's directory name.
 // For numeric input, returns the engine's canonical casing. For
 // string input, returns the input verbatim once existence is
-// confirmed.
+// confirmed; nil for an unregistered name.
+//
+// String-input existence isn't free: `ResolveAddOnName` echoes the
+// string for the field accessors below (`GetAddOnTitle`, etc.) which
+// short-circuit cleanly on unknown names via the engine's own NULL-
+// return paths. `GetAddOnName` doesn't call any engine accessor, so
+// it'd otherwise echo any string. Probe the registry explicitly.
 int __fastcall Script_GetAddOnName(void *L) {
     const uint8_t *entry = ResolveAddOnName(L);
     if (entry == nullptr) {
         Game::Lua::PushNil(L);
         return 1;
     }
+    if (Game::Lua::Type(L, 1) == Game::Lua::TYPE_STRING &&
+        !AddOnExistsByName(reinterpret_cast<const char *>(entry))) {
+        Game::Lua::PushNil(L);
+        return 1;
+    }
     Game::Lua::PushString(L, reinterpret_cast<const char *>(entry));
     return 1;
 }

src/equipmentset/Api.cpp

@@ -424,60 +424,136 @@ int __fastcall Script_UseEquipmentSet(void *L) {
     }
     int nextFreeSlot = 0;
 
+    // Pre-snapshot each set item's location against the ORIGINAL
+    // state, before any swap packets fly. This mirrors how 4.3.4's
+    // `Script_UseEquipmentSet` (`0x009A15D0`) builds its action list:
+    // resolve all 19 source locations up front, then execute. The
+    // engine's CGItem / InvMgr state lags behind our packet sends
+    // (waits for server ACK), so any `FindGUID` mid-execution would
+    // return stale answers and we'd re-resolve items into the wrong
+    // place.
+    int sourceLoc[SLOT_COUNT];
+    for (int i = 0; i < SLOT_COUNT; ++i) {
+        const uint64_t g = guids[i];
+        if (g == GUID_EMPTY || g == GUID_IGNORED) {
+            sourceLoc[i] = 0;
+            continue;
+        }
+        sourceLoc[i] = Locations::FindGUID(g);
+    }
+
+    // Virtual paperdoll occupant model — seeded from the engine's
+    // initial paperdoll GUID array, then updated in-place after each
+    // swap so phase 1 can chain rotations and phase 3 can spot
+    // already-empty slots.
+    uint64_t virtualPaperdoll[SLOT_COUNT];
+    Locations::SnapshotPaperdoll(virtualPaperdoll);
+
+    // Locates the current virtual slot of a GUID on the paperdoll,
+    // or 0 if it's not currently there. Used during phase 1 so
+    // chained paperdoll-to-paperdoll moves operate on the *current*
+    // virtual position, not the stale pre-snapshot.
+    auto currentPaperdollSlot = [&](uint64_t g) -> int {
+        if (g == 0)
+            return 0;
+        for (int slot = 1; slot <= SLOT_COUNT; ++slot) {
+            if (virtualPaperdoll[slot - 1] == g)
+                return slot;
+        }
+        return 0;
+    };
+
+    // ── Phase 1: paperdoll → paperdoll ─────────────────────────────
+    // Move items already on the paperdoll into their target slots.
+    // Source and destination are both paperdoll, so atomic swaps
+    // never touch bag state — phase 2's bag lookups stay accurate.
     for (int i = 0; i < SLOT_COUNT; ++i) {
         const int targetSlot = i + 1;
         const uint64_t g = guids[i];
-
-        // GUID_IGNORED: leave whatever the player has in this slot
-        // as-is. Distinct from GUID_EMPTY (= 0), which means "this
-        // slot should be empty after the swap" — handled below.
-        if (g == GUID_IGNORED)
+        if (g == GUID_EMPTY || g == GUID_IGNORED)
             continue;
 
-        if (g == GUID_EMPTY) {
-            // Set wants this slot empty. If it already is, no-op.
-            // Otherwise unequip whatever's there into the next bag
-            // slot we reserved during the pre-loop snapshot. If
-            // we've exhausted the snapshot, silently skip — matches
-            // the modern API which surfaces no per-slot reason.
-            const uint8_t *equipped =
-                Item::Location::ResolveEquipmentSlot(targetSlot);
-            if (equipped == nullptr)
-                continue;
-            if (nextFreeSlot >= freeSlotCount)
-                continue;
-            const FreeSlot &fs = freeSlots[nextFreeSlot++];
-            Item::Swap::ToBag(equipped, targetSlot, fs.bag, fs.slot);
-            continue;
-        }
-
-        const int loc = Locations::FindGUID(g);
+        const int loc = sourceLoc[i];
         if (loc == 0)
-            continue; // missing — nothing to do
-
-        // Already in its target slot? Skip.
-        if ((loc & LOC_BAGS) == 0 && (loc & LOC_BANK) == 0 &&
-            (loc & LOC_SLOT_MASK) == targetSlot)
             continue;
-
-        // In bank (main or bank-bag) — server rejects equip-from-bank.
         if (loc & LOC_BANK)
-            continue;
+            continue; // server rejects equip-from-bank
+        if (loc & LOC_BAGS)
+            continue; // phase 2
+
+        const int srcSlot = currentPaperdollSlot(g);
+        if (srcSlot == 0 || srcSlot == targetSlot)
+            continue; // missing or already there
 
         const uint8_t *item = Locations::ResolveItemByGUID(g);
         if (item == nullptr)
             continue;
 
-        if (loc & LOC_BAGS) {
-            const int srcBag = (loc >> LOC_BAG_SHIFT) & 0xFF;
-            const int srcSlot = loc & LOC_SLOT_MASK;
-            Item::Swap::FromBag(item, srcBag, srcSlot, targetSlot);
-        } else {
-            const int srcSlot = loc & LOC_SLOT_MASK;
-            Item::Swap::FromPaperdoll(item, srcSlot, targetSlot);
+        const uint64_t displaced = virtualPaperdoll[targetSlot - 1];
+        if (Item::Swap::FromPaperdoll(item, srcSlot, targetSlot)) {
+            virtualPaperdoll[targetSlot - 1] = g;
+            virtualPaperdoll[srcSlot - 1] = displaced;
         }
     }
 
+    // ── Phase 2: bag → paperdoll ───────────────────────────────────
+    // Move items from bag slots onto the paperdoll. Each atomic swap
+    // displaces the current paperdoll occupant into the bag slot the
+    // incoming item vacated. Anything we still wanted on the paperdoll
+    // was already placed by phase 1, so phase 2 displacements can't
+    // strand a future set item in a bag.
+    for (int i = 0; i < SLOT_COUNT; ++i) {
+        const int targetSlot = i + 1;
+        const uint64_t g = guids[i];
+        if (g == GUID_EMPTY || g == GUID_IGNORED)
+            continue;
+        if (virtualPaperdoll[targetSlot - 1] == g)
+            continue; // already at target (probably by phase 1)
+
+        const int loc = sourceLoc[i];
+        if (loc == 0)
+            continue;
+        if (loc & LOC_BANK)
+            continue;
+        if ((loc & LOC_BAGS) == 0)
+            continue; // not from a bag — phase 1 handled, or item missing
+
+        const uint8_t *item = Locations::ResolveItemByGUID(g);
+        if (item == nullptr)
+            continue;
+
+        const int srcBag = (loc >> LOC_BAG_SHIFT) & 0xFF;
+        const int srcSlot = loc & LOC_SLOT_MASK;
+        if (Item::Swap::FromBag(item, srcBag, srcSlot, targetSlot)) {
+            virtualPaperdoll[targetSlot - 1] = g;
+            // The displaced item lands in (srcBag, srcSlot). We
+            // don't track bag-side virtual state — by phase 3 we
+            // only care about the paperdoll occupant.
+        }
+    }
+
+    // ── Phase 3: unequip slots the set wants empty ─────────────────
+    // For each `GUID_EMPTY` slot, send the current paperdoll occupant
+    // (if any) to a pre-snapshotted free bag slot. Runs last so any
+    // displaced items from phases 1/2 that landed in the slot get
+    // unequipped here too.
+    for (int i = 0; i < SLOT_COUNT; ++i) {
+        const int targetSlot = i + 1;
+        if (guids[i] != GUID_EMPTY)
+            continue;
+        const uint64_t occupant = virtualPaperdoll[targetSlot - 1];
+        if (occupant == 0)
+            continue;
+        if (nextFreeSlot >= freeSlotCount)
+            continue;
+        const uint8_t *equipped = Locations::ResolveItemByGUID(occupant);
+        if (equipped == nullptr)
+            continue;
+        const FreeSlot &fs = freeSlots[nextFreeSlot++];
+        if (Item::Swap::ToBag(equipped, targetSlot, fs.bag, fs.slot))
+            virtualPaperdoll[targetSlot - 1] = 0;
+    }
+
     const int evt = Event::Custom::Lookup(kSwapFinishedEvent);
     if (evt >= 0)
         Event::Custom::Fire(evt, "%d%d", 1, static_cast<int>(setID));

src/equipmentset/Locations.cpp

@@ -177,4 +177,15 @@ const uint8_t *ResolveItemByGUID(uint64_t guid) {
     return Item::Location::ResolveByGUID(guid);
 }
 
+void SnapshotPaperdoll(uint64_t *out) {
+    for (int i = 0; i < SLOT_COUNT; ++i)
+        out[i] = 0;
+    auto *invMgr = ResolvePlayerInvMgr();
+    auto *guids = InvMgrGuidArray(invMgr);
+    if (guids == nullptr)
+        return;
+    for (int i = 0; i < SLOT_COUNT; ++i)
+        out[i] = guids[i];
+}
+
 } // namespace EquipmentSet::Locations

src/equipmentset/Locations.h

@@ -42,4 +42,16 @@ int FindGUID(uint64_t targetGuid);
 // isn't known to the client. Side-effect free.
 const uint8_t *ResolveItemByGUID(uint64_t guid);
 
+// Copies the current paperdoll GUIDs into `out[0..SLOT_COUNT-1]`,
+// where `out[i]` is the GUID at 1-based equipment slot `i+1`.
+// Empty / unequipped slots write 0. Reads from the player invMgr's
+// flat GUID array directly — no Lua stack, no engine state changes.
+//
+// Used by `UseEquipmentSet` to seed a "virtual paperdoll" model that
+// stays current across in-flight swaps. The engine's CGItem state
+// lags behind packet sends (server has to ACK each swap), so any
+// subsequent `FindGUID` after the first packet would return stale
+// pre-swap locations. Tracking moves locally bypasses that lag.
+void SnapshotPaperdoll(uint64_t *out);
+
 } // namespace EquipmentSet::Locations

src/input/GlobalMouse.cpp

@@ -18,6 +18,12 @@
 // per-frame `OnMouseDown` scripts — these fire even when the click
 // misses any UI frame.
 //
+// `IsMouseButtonDown([button])` — query the current held state of a
+// specific button by name or 1-based ID, or "any button held" when
+// called with no args. State is maintained from the same hook stream
+// as the events (single source of truth — events firing and the
+// state being readable happen at the same point in the pipeline).
+//
 // Same `WH_GETMESSAGE` thread-message hook pattern as
 // [Input::Modifier](Modifier.cpp): we intercept the WM_*BUTTON*
 // messages on the engine's main thread *before* dispatch. The hook
@@ -28,6 +34,9 @@
 #include "Game.h"
 #include "event/Custom.h"
 
+#include <cstdint>
+#include <cstring>
+
 #include <windows.h>
 
 namespace Input::GlobalMouse {
@@ -37,6 +46,19 @@ namespace {
 constexpr const char *kDownEvent = "GLOBAL_MOUSE_DOWN";
 constexpr const char *kUpEvent   = "GLOBAL_MOUSE_UP";
 
+// Held-state bitmap — bit `i` set means the button with 1-based
+// `IsMouseButtonDown` ID `i+1` is currently held. Modern API IDs:
+//   1 = LeftButton, 2 = RightButton, 3 = MiddleButton,
+//   4 = Button4    (XBUTTON1), 5 = Button5 (XBUTTON2).
+constexpr int BIT_LEFT_BUTTON   = 0;
+constexpr int BIT_RIGHT_BUTTON  = 1;
+constexpr int BIT_MIDDLE_BUTTON = 2;
+constexpr int BIT_BUTTON4       = 3;
+constexpr int BIT_BUTTON5       = 4;
+constexpr uint32_t MASK_ANY_BUTTON = 0x1F;
+
+uint32_t g_mouseButtonMask = 0;
+
 HHOOK g_msgHook = nullptr;
 
 // Maps WM_*BUTTON{DOWN,UP} → ("LeftButton"|..., isDown). Returns
@@ -60,16 +82,60 @@ const char *DecodeButton(UINT msg, WPARAM wParam, bool *outDown) {
     }
 }
 
+// Maps a "LeftButton"/.../"Button5" name to its bit index. -1 for
+// any other string.
+int NameToBitIdx(const char *name) {
+    if (name == nullptr)
+        return -1;
+    if (std::strcmp(name, "LeftButton") == 0)   return BIT_LEFT_BUTTON;
+    if (std::strcmp(name, "RightButton") == 0)  return BIT_RIGHT_BUTTON;
+    if (std::strcmp(name, "MiddleButton") == 0) return BIT_MIDDLE_BUTTON;
+    if (std::strcmp(name, "Button4") == 0)      return BIT_BUTTON4;
+    if (std::strcmp(name, "Button5") == 0)      return BIT_BUTTON5;
+    return -1;
+}
+
 void ProcessMouseMessage(UINT msg, WPARAM wParam) {
     bool down = false;
     const char *name = DecodeButton(msg, wParam, &down);
     if (name == nullptr)
         return;
+
+    const int bitIdx = NameToBitIdx(name);
+    if (bitIdx >= 0) {
+        const uint32_t bit = 1u << bitIdx;
+        if (down) g_mouseButtonMask |= bit;
+        else      g_mouseButtonMask &= ~bit;
+    }
+
     const int slot = Event::Custom::Lookup(down ? kDownEvent : kUpEvent);
     if (slot >= 0)
         Event::Custom::Fire(slot, "%s", name);
 }
 
+int __fastcall Script_IsMouseButtonDown(void *L) {
+    bool down;
+    if (Game::Lua::GetTop(L) == 0) {
+        // No-arg form: any button held.
+        down = (g_mouseButtonMask & MASK_ANY_BUTTON) != 0;
+    } else {
+        int bitIdx = -1;
+        if (Game::Lua::IsNumber(L, 1)) {
+            const int id = static_cast<int>(Game::Lua::ToNumber(L, 1));
+            if (id >= 1 && id <= 5)
+                bitIdx = id - 1;
+        } else if (Game::Lua::IsString(L, 1)) {
+            bitIdx = NameToBitIdx(Game::Lua::ToString(L, 1));
+        }
+        // Unrecognized button (bad id, unknown name) → false, matching
+        // the modern API's "did this specific button happen to be held"
+        // semantic. Bad input doesn't promote to the any-button check.
+        down = (bitIdx >= 0) && (g_mouseButtonMask & (1u << bitIdx)) != 0;
+    }
+    Game::Lua::PushBool(L, down);
+    return 1;
+}
+
 LRESULT CALLBACK GetMsgHook(int code, WPARAM wParam, LPARAM lParam) {
     // Only process when the message is being removed from the queue
     // (`PM_REMOVE` / `GetMessage`); `PM_NOREMOVE` peeks would deliver
@@ -88,7 +154,11 @@ void InstallHook() {
                                    GetCurrentThreadId());
 }
 
-void RegisterLuaFunctions() { InstallHook(); }
+void RegisterLuaFunctions() {
+    Game::Lua::RegisterGlobalFunction("IsMouseButtonDown",
+                                      &Script_IsMouseButtonDown);
+    InstallHook();
+}
 
 const Event::Custom::AutoReserve _reserveDown{kDownEvent};
 const Event::Custom::AutoReserve _reserveUp{kUpEvent};

src/item/InventoryItemsForSlot.cpp

@@ -105,6 +105,47 @@ bool FitsSlot(int slot1Based, uint32_t invType) {
     return (kSlotMaskByInvType[invType] & (1u << (slot1Based - 1))) != 0;
 }
 
+// ── Proficiency gate ──────────────────────────────────────────────
+// `FitsSlot` only checks invType→slot shape compatibility; without
+// also gating on the player's proficiencies this would return (e.g.)
+// mail helms for a warlock since both are `invType=HEAD`. Modern
+// WoW's equipment-set picker filters by what the player can actually
+// equip; we mirror that.
+//
+// Source of truth: the engine's per-itemClass proficiency bitmap at
+// `[VAR_PROFICIENCY_TABLE]` (17 u32 entries indexed by `m_class`).
+// SMSG_SET_PROFICIENCY's handler at `0x005E7B70` writes the bitmask
+// for each class verbatim from the wire. Bit N of `table[class]` =
+// "player can equip subclass N of this class". Same data the engine
+// itself reads for the tooltip "Mail/Leather/Plate" red-text and the
+// cursor-drop-on-paperdoll-slot check — covers both armor and weapon
+// proficiencies in one lookup.
+//
+// 4.3.4's `Script_GetInventoryItemsForSlot` does the equivalent check
+// via `FUN_00553AD0(itemClass) & (1 << subclass)`, reading from
+// `DAT_00DD4D38` (its own copy of the same packet-fed table).
+
+bool PlayerHasProficiency(uint32_t itemClass, uint32_t subclass) {
+    if (itemClass > 16)
+        return true; // table only covers 0..16; be permissive past that
+    const uint32_t mask = *reinterpret_cast<const uint32_t *>(
+        static_cast<uintptr_t>(Offsets::VAR_PROFICIENCY_TABLE) + itemClass * 4);
+    if (mask == 0)
+        return true; // table not populated yet (pre-SMSG_SET_PROFICIENCY)
+                     // — fail open so empty-mask doesn't blank the list
+    return (mask & (1u << subclass)) != 0;
+}
+
+bool PlayerCanEquip(const uint8_t *record) {
+    if (record == nullptr)
+        return true; // missing record — be permissive, don't hide the item
+    const uint32_t classCode = *reinterpret_cast<const uint32_t *>(
+        record + Offsets::OFF_ITEMSTATS_CLASS);
+    const uint32_t subclass = *reinterpret_cast<const uint32_t *>(
+        record + Offsets::OFF_ITEMSTATS_SUBCLASS);
+    return PlayerHasProficiency(classCode, subclass);
+}
+
 const uint8_t *PeekItemRecord(uint32_t itemID) {
     auto fn = reinterpret_cast<GetItemRecord_t>(Offsets::FUN_DBCACHE_ITEMSTATS_GET_RECORD);
     auto *cache = reinterpret_cast<void *>(Offsets::VAR_ITEMDB_CACHE);
@@ -112,11 +153,14 @@ const uint8_t *PeekItemRecord(uint32_t itemID) {
     return fn(cache, itemID, &zeroGuid, nullptr, nullptr, 0);
 }
 
-uint32_t ReadInventoryType(const uint8_t *cgItem) {
+const uint8_t *ItemRecordForCGItem(const uint8_t *cgItem) {
     const int itemID = Item::ID::FromCGItem(cgItem);
     if (itemID <= 0)
-        return 0;
-    auto *record = PeekItemRecord(static_cast<uint32_t>(itemID));
+        return nullptr;
+    return PeekItemRecord(static_cast<uint32_t>(itemID));
+}
+
+uint32_t ReadInventoryType(const uint8_t *record) {
     if (record == nullptr)
         return 0;
     return *reinterpret_cast<const uint32_t *>(
@@ -132,7 +176,10 @@ void CollectIfFits(int slot, const uint8_t *cgItem, int location,
                    std::vector<Hit> &out) {
     if (cgItem == nullptr)
         return;
-    if (!FitsSlot(slot, ReadInventoryType(cgItem)))
+    const uint8_t *record = ItemRecordForCGItem(cgItem);
+    if (!FitsSlot(slot, ReadInventoryType(record)))
+        return;
+    if (!PlayerCanEquip(record))
         return;
     out.push_back({location, cgItem});
 }