Equipment: weapon-granted abilities + gear mods (DR-027 Phase 1)

Equipment slots reusing the AbilityRef/StatModifier machinery: EquipmentSlot [GhostField] buffer (index=slot), server-only event-driven EquipSystem (RPC). Weapon -> AbilityRef.Id swaps the attack (prefab + base stats, prediction-correct); gear -> StatModifiers tagged a reserved per-slot EquipSourceId, stripped target-agnostically via RemoveBySourceId. Item mods are INLINE on ItemDefBlob (a nested BlobArray reads empty under the by-value TryGetItem copy). Atomic equip-over swap (no item loss); DefaultAbility restores the unarmed ability on weapon-unequip. Client keys + build-safe hooks; HUD equipment panel + click-to-equip. 4 catalog weapon/gear items wired + re-baked.

Play-validated host+client: weapon equip swaps AbilityRef on both worlds, gear folds into EffectiveCharacterStats, unequip reverses + restores DefaultAbility, all replicated to the owner. See DR-027.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Assets/_Project/Scripts/Simulation/Items/InventoryMath.cs

@@ -76,6 +76,27 @@ namespace ProjectM.Simulation
             return taken;
         }
 
+        /// <summary>
+        /// Non-mutating check: would depositing <paramref name="count"/> of <paramref name="itemId"/> FULLY fit
+        /// (top-up existing stacks + new stacks within <paramref name="maxSlots"/>)? Used by the equip swap to
+        /// guarantee the swapped-out item has room BEFORE any withdrawal (no item loss). Mirrors Deposit's space math.
+        /// </summary>
+        public static bool CanDeposit(DynamicBuffer<InventorySlot> buffer, ushort itemId, int count, int stackMax, int maxSlots)
+        {
+            if (count <= 0) return true;
+            if (itemId == 0) return false;
+            if (stackMax < 1) stackMax = int.MaxValue;
+
+            long space = 0;
+            for (int i = 0; i < buffer.Length; i++)
+                if (buffer[i].ItemId == itemId)
+                    space += stackMax - buffer[i].Count;
+            int freeSlots = maxSlots - buffer.Length;
+            if (freeSlots > 0)
+                space += (long)freeSlots * stackMax;
+            return space >= count;
+        }
+
         /// <summary>Total quantity of <paramref name="itemId"/> across all stacks (0 if absent).</summary>
         public static int CountOf(DynamicBuffer<InventorySlot> buffer, ushort itemId)
         {