## Problem
A creature equipped with two items that resolve to the **same layer** can crash the legacy EA 2D client (use-after-free). Equipment `Layer` comes from tiledata (`Layer = (Layer)ItemData.Quality`), so a **two-handed weapon and a shield both resolve to `Layer.TwoHanded`**. `Mobile.FindItemOnLayer` even documents the invariant: *"We only allow 1 item per layer. Its an implicit contract."*
## Root cause
- `SendMobileIncoming` (0x78) **dedupes by layer** (the `layers` span) and sends only the first item per slot — so a static creature is fine.
- But the per-item **`SendEquipUpdate` (0x2E)** and the item **OPL** sends do **not** dedupe. On any equip/property delta (`Item.ProcessDelta`) they fire per item and leak the second same-layer item on its own.
- The client then holds two items on one equipment slot; when that slot is torn down (e.g. a large group of such creatures and the player runs out of range → mass remove) the legacy 2D client frees one and dereferences it → UAF. ClassicUO bounds-checks and is unaffected, but the server is emitting an invalid, self-contradictory stream either way.
## Fix
Make per-item equip/OPL sends honor the same first-item-per-layer rule `SendMobileIncoming` already uses:
- `Item.IsDupedEquipLayer()` — `m_Parent is Mobile m && m.FindItemOnLayer(m_Layer) != this` (reuses the existing helper; true when an earlier item already holds this items layer).
- `Item.ProcessDelta`: early-return before the per-client loop for a duped equipped item (skips the EquipUpdate and OPL to everyone).
- `Mobile` lift-reject re-show: skip the EquipUpdate and OPL for the dupe.
No behavioral change for valid equipment (distinct layers → never duped). For the invalid duped-layer case the second item was already omitted by the 0x78 packet; this just stops it leaking back via the per-item paths.
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