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/Items/Item_AetherVest.asset

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+  m_Name: Item_AetherVest
+  m_EditorClassIdentifier: ProjectM.Authoring::ProjectM.Authoring.ItemDefinition
+  ItemId: 22
+  DisplayName: Aether Vest
+  Category: 3
+  Tier: 1
+  StackMax: 1
+  EquipSlot: 1
+  GrantedAbilityId: 0
+  Mods:
+  - Target: 6
+    Op: 1
+    Value: 0.15

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Assets/_Project/Items/Item_HeavyCannon.asset

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+  m_Name: Item_HeavyCannon
+  m_EditorClassIdentifier: ProjectM.Authoring::ProjectM.Authoring.ItemDefinition
+  ItemId: 21
+  DisplayName: Heavy Cannon
+  Category: 2
+  Tier: 1
+  StackMax: 1
+  EquipSlot: 0
+  GrantedAbilityId: 3
+  Mods:
+  - Target: 0
+    Op: 0
+    Value: 10

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Assets/_Project/Items/Item_PowerSigil.asset

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+  m_Name: Item_PowerSigil
+  m_EditorClassIdentifier: ProjectM.Authoring::ProjectM.Authoring.ItemDefinition
+  ItemId: 23
+  DisplayName: Power Sigil
+  Category: 3
+  Tier: 1
+  StackMax: 1
+  EquipSlot: 2
+  GrantedAbilityId: 0
+  Mods:
+  - Target: 0
+    Op: 1
+    Value: 0.2

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Assets/_Project/Items/Item_RapidBlaster.asset

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+  m_Name: Item_RapidBlaster
+  m_EditorClassIdentifier: ProjectM.Authoring::ProjectM.Authoring.ItemDefinition
+  ItemId: 20
+  DisplayName: Rapid Blaster
+  Category: 2
+  Tier: 1
+  StackMax: 1
+  EquipSlot: 0
+  GrantedAbilityId: 2
+  Mods: []

Assets/_Project/Items/Item_RapidBlaster.asset.meta

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Assets/_Project/Scripts/Authoring/Items/ItemDatabaseAuthoring.cs

@@ -40,6 +40,12 @@ namespace ProjectM.Authoring
                         Category = def.Category,
                         Tier = def.Tier,
                         StackMax = def.StackMax,
+                        EquipSlot = def.EquipSlot,
+                        GrantedAbilityId = def.GrantedAbilityId,
+                        Mod0 = ModAt(def, 0),
+                        Mod1 = ModAt(def, 1),
+                        Mod2 = ModAt(def, 2),
+                        Mod3 = ModAt(def, 3),
                         Name = def.DisplayName,
                     };
                 }
@@ -48,6 +54,16 @@ namespace ProjectM.Authoring
                 builder.Dispose();
                 AddBlobAsset(ref blob, out _);
                 AddComponent(entity, new ItemDatabase { Value = blob });
+
+                static ItemModSpec ModAt(ItemDefinition def, int i)
+                {
+                    if (def.Mods != null && i < def.Mods.Count)
+                    {
+                        var m = def.Mods[i];
+                        return new ItemModSpec { Target = m.Target, Op = m.Op, Value = m.Value };
+                    }
+                    return new ItemModSpec { Target = 255 };
+                }
             }
         }
     }

Assets/_Project/Scripts/Authoring/Items/ItemDefinition.cs

@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using ProjectM.Simulation;
 using UnityEngine;
 
@@ -27,5 +28,26 @@ namespace ProjectM.Authoring
         [Min(1)]
         [Tooltip("Max units that stack in one inventory slot (1 for non-stacking equipment).")]
         public int StackMax = 999;
+
+        [Header("Equipment (Phase 1)")]
+        [Tooltip("EquipSlotId byte: 0=Weapon, 1=Armor, 2=Trinket, 3=Tool, 255=not equippable.")]
+        public byte EquipSlot = 255;
+
+        [Tooltip("AbilityId granted when equipped in the Weapon slot (0=none): 1=Primary, 2=FastLight, 3=SlowHeavy.")]
+        public byte GrantedAbilityId = 0;
+
+        [Tooltip("Stat modifiers granted while equipped (first 4 used).")]
+        public List<ItemModAuthoring> Mods = new List<ItemModAuthoring>();
+    }
+
+    /// <summary>Designer-facing stat-mod grant on an equippable item; the baker writes the first 4 into ItemDefBlob's inline mod slots.</summary>
+    [System.Serializable]
+    public struct ItemModAuthoring
+    {
+        [Tooltip("StatTarget byte: 0=Damage,1=CooldownTicks,2=Range,3=ProjectileSpeed,4=AutoTargetRange,5=AutoTargetCone,6=MoveSpeed,7=TurnRate,8=MaxHealth.")]
+        public byte Target;
+        [Tooltip("ModOp byte: 0=Flat, 1=PercentAdd, 2=PercentMult.")]
+        public byte Op;
+        public float Value;
     }
 }

Assets/_Project/Scripts/Authoring/Player/PlayerAuthoring.cs

@@ -60,6 +60,8 @@ namespace ProjectM.Authoring
                 // Data-driven stat refs (replace M2's inlined PlayerMoveStats / AbilityStats values).
                 AddComponent(entity, new CharacterStatsRef { Id = characterId });
                 AddComponent(entity, new AbilityRef { Id = abilityId });
+                // Unarmed/base ability restored on weapon-unequip (AbilityRef.Id mutates when a weapon is equipped).
+                AddComponent(entity, new DefaultAbility { Id = abilityId });
 
                 // Effective stats: zeroed at bake, recomputed every predicted tick by StatRecomputeSystem.
                 AddComponent(entity, new EffectiveAbilityStats());
@@ -69,6 +71,10 @@ namespace ProjectM.Authoring
                 AddBuffer<StatModifier>(entity);
                 // Empty replicated personal inventory (server-authoritative; harvest yield + deposit RPC land here).
                 AddBuffer<InventorySlot>(entity);
+                // Equipment loadout: one replicated row per slot in FIXED order (buffer index = EquipSlotId), empty.
+                var equip = AddBuffer<EquipmentSlot>(entity);
+                for (int s = 0; s < EquipSlotId.Count; s++)
+                    equip.Add(new EquipmentSlot { ItemId = 0 });
                 // Server-only expiry tracker for timed buffs (paired with a StatModifier by SourceId; not replicated).
                 AddBuffer<TimedModifier>(entity);
 

Assets/_Project/Scripts/Client/Economy/EquipSendSystem.cs

@@ -0,0 +1,116 @@
+using ProjectM.Simulation;
+using Unity.Entities;
+using Unity.NetCode;
+
+namespace ProjectM.Client
+{
+    /// <summary>
+    /// Client-only sender for <see cref="EquipRequest"/> / <see cref="UnequipRequest"/> RPCs. One-off actions, so
+    /// RPCs (not per-tick input); the server applies them authoritatively in
+    /// <see cref="ProjectM.Server.EquipSystem"/>. Number keys 1-9 equip the Nth EQUIPPABLE item in the local bag
+    /// (resources are skipped via the catalog); U unequips the weapon. Managed SystemBase because it reads the
+    /// managed Input System; Input System types are fully qualified and <c>using UnityEngine.InputSystem;</c> is
+    /// omitted (it defines a colliding PlayerInput type). An <c>#if UNITY_EDITOR</c> static hook drives the same
+    /// path from execute_code for headless validation. The HUD click-to-equip (HudSystem) is the primary UX;
+    /// these keys are the reachable fallback. Wire types are unconditional; only this send SYSTEM is gated.
+    /// </summary>
+    [WorldSystemFilter(WorldSystemFilterFlags.ClientSimulation)]
+    public partial class EquipSendSystem : SystemBase
+    {
+        struct PendingEquip { public bool Unequip; public ushort ItemId; public byte Slot; }
+
+        static readonly System.Collections.Generic.Queue<PendingEquip> s_Pending =
+            new System.Collections.Generic.Queue<PendingEquip>();
+
+        /// <summary>EDITOR / execute_code hook: queue an equip of <paramref name="itemId"/> from the bag.</summary>
+        public static void Equip(ushort itemId) =>
+            s_Pending.Enqueue(new PendingEquip { Unequip = false, ItemId = itemId });
+
+        /// <summary>EDITOR / execute_code hook: queue an unequip of <paramref name="slot"/> (an EquipSlotId).</summary>
+        public static void Unequip(byte slot) =>
+            s_Pending.Enqueue(new PendingEquip { Unequip = true, Slot = slot });
+
+        protected override void OnCreate()
+        {
+            RequireForUpdate<NetworkId>();
+        }
+
+        protected override void OnUpdate()
+        {
+            if (!SystemAPI.TryGetSingletonEntity<NetworkId>(out var connection))
+                return;
+
+            var keyboard = UnityEngine.InputSystem.Keyboard.current;
+            if (keyboard != null)
+            {
+                int n = NumberKeyPressed(keyboard);
+                if (n >= 0)
+                {
+                    ushort itemId = NthEquippableBagItem(n);
+                    if (itemId != 0) SendEquip(connection, itemId);
+                }
+                if (keyboard.uKey.wasPressedThisFrame)
+                    SendUnequip(connection, EquipSlotId.Weapon);
+            }
+
+            while (s_Pending.Count > 0)
+            {
+                var p = s_Pending.Dequeue();
+                if (p.Unequip) SendUnequip(connection, p.Slot);
+                else SendEquip(connection, p.ItemId);
+            }
+        }
+
+        static int NumberKeyPressed(UnityEngine.InputSystem.Keyboard kb)
+        {
+            if (kb.digit1Key.wasPressedThisFrame) return 0;
+            if (kb.digit2Key.wasPressedThisFrame) return 1;
+            if (kb.digit3Key.wasPressedThisFrame) return 2;
+            if (kb.digit4Key.wasPressedThisFrame) return 3;
+            if (kb.digit5Key.wasPressedThisFrame) return 4;
+            if (kb.digit6Key.wasPressedThisFrame) return 5;
+            if (kb.digit7Key.wasPressedThisFrame) return 6;
+            if (kb.digit8Key.wasPressedThisFrame) return 7;
+            if (kb.digit9Key.wasPressedThisFrame) return 8;
+            return -1;
+        }
+
+        /// <summary>Resolve the Nth EQUIPPABLE distinct item in the local player's bag (skips resources via the catalog).</summary>
+        ushort NthEquippableBagItem(int n)
+        {
+            bool haveDb = SystemAPI.TryGetSingleton<ItemDatabase>(out var db);
+            foreach (var bag in SystemAPI.Query<DynamicBuffer<InventorySlot>>().WithAll<GhostOwnerIsLocal, PlayerTag>())
+            {
+                int idx = 0;
+                for (int i = 0; i < bag.Length; i++)
+                {
+                    ushort id = bag[i].ItemId;
+                    if (id == 0 || bag[i].Count <= 0) continue;
+                    if (haveDb && db.Value.IsCreated)
+                    {
+                        ref var b = ref db.Value.Value;
+                        if (!b.TryGetItem(id, out var def) || def.EquipSlot >= EquipSlotId.Count) continue;
+                    }
+                    if (idx == n) return id;
+                    idx++;
+                }
+                break;
+            }
+            return 0;
+        }
+
+        void SendEquip(Entity connection, ushort itemId)
+        {
+            var req = EntityManager.CreateEntity();
+            EntityManager.AddComponentData(req, new EquipRequest { ItemId = itemId });
+            EntityManager.AddComponentData(req, new SendRpcCommandRequest { TargetConnection = connection });
+        }
+
+        void SendUnequip(Entity connection, byte slot)
+        {
+            var req = EntityManager.CreateEntity();
+            EntityManager.AddComponentData(req, new UnequipRequest { Slot = slot });
+            EntityManager.AddComponentData(req, new SendRpcCommandRequest { TargetConnection = connection });
+        }
+    }
+}

Assets/_Project/Scripts/Client/Economy/EquipSendSystem.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 7a9bec24b84553746aec834c1b56dfd6

Assets/_Project/Scripts/Client/Presentation/HudSystem.cs

@@ -71,7 +71,7 @@ namespace ProjectM.Client
         float _prevHp, _flash;
         bool _haveHp;
         // personal inventory panel (read-only; toggled with I)
-        VisualElement _invPanel, _invList;
+        VisualElement _invPanel, _invList, _equipList;
         bool _invOpen;
 
         EntityQuery _huskQuery;
@@ -299,8 +299,10 @@ namespace ProjectM.Client
             if (_invOpen && found)
             {
                 EntityManager.CompleteDependencyBeforeRO<InventorySlot>();
+                EntityManager.CompleteDependencyBeforeRO<EquipmentSlot>();
                 bool haveItemDb = SystemAPI.TryGetSingleton<ItemDatabase>(out var itemDb);
                 _invPanel.style.display = DisplayStyle.Flex;
+
                 _invList.Clear();
                 int shown = 0;
                 foreach (var bag in SystemAPI.Query<DynamicBuffer<InventorySlot>>()
@@ -310,13 +312,27 @@ namespace ProjectM.Client
                     {
                         var slot = bag[i];
                         if (slot.ItemId == 0 || slot.Count <= 0) continue;
-                        AddInvRow(ItemName(haveItemDb, itemDb, slot.ItemId), ItemTint(slot.ItemId), slot.Count);
+                        AddInvRow(slot.ItemId, ItemName(haveItemDb, itemDb, slot.ItemId), ItemTint(slot.ItemId), slot.Count,
+                            IsEquippable(haveItemDb, itemDb, slot.ItemId));
                         shown++;
                     }
                     break;
                 }
                 if (shown == 0)
                     _invList.Add(HudUi.Text("(empty)", 13, MenuUi.SubCol, TextAnchor.MiddleLeft));
+
+                _equipList.Clear();
+                foreach (var slots in SystemAPI.Query<DynamicBuffer<EquipmentSlot>>()
+                             .WithAll<GhostOwnerIsLocal, PlayerTag>())
+                {
+                    for (byte s = 0; s < EquipSlotId.Count && s < slots.Length; s++)
+                    {
+                        ushort id = slots[s].ItemId;
+                        string label = SlotName(s) + ":  " + (id == 0 ? "-" : ItemName(haveItemDb, itemDb, id));
+                        AddEquipRow(s, label, id != 0);
+                    }
+                    break;
+                }
             }
             else
             {
@@ -776,7 +792,15 @@ namespace ProjectM.Client
             _invList.pickingMode = PickingMode.Ignore;
             _invPanel.Add(_invList);
 
-            var hint = HudUi.Text("I close   -   G deposit all at base", 11, MenuUi.SubCol, TextAnchor.MiddleLeft);
+            var equipHeader = HudUi.Display("EQUIPMENT", 14, AetherCyan, TextAnchor.MiddleLeft);
+            equipHeader.style.marginTop = 8; equipHeader.style.marginBottom = 4;
+            _invPanel.Add(equipHeader);
+
+            _equipList = new VisualElement();
+            _equipList.pickingMode = PickingMode.Ignore;
+            _invPanel.Add(_equipList);
+
+            var hint = HudUi.Text("I close   -   click item=equip / slot=unequip   -   G deposit", 11, MenuUi.SubCol, TextAnchor.MiddleLeft);
             hint.style.marginTop = 8;
             _invPanel.Add(hint);
 
@@ -784,16 +808,22 @@ namespace ProjectM.Client
             root.Add(_invPanel);
         }
 
-        void AddInvRow(string name, Color tint, int count)
+        void AddInvRow(ushort itemId, string name, Color tint, int count, bool equippable)
         {
             var row = new VisualElement();
             row.style.flexDirection = FlexDirection.Row;
             row.style.justifyContent = Justify.SpaceBetween;
             row.style.minWidth = 196;
             row.style.marginTop = 2;
-            row.pickingMode = PickingMode.Ignore;
+            row.Add(HudUi.Text(name + (equippable ? "  (equip)" : ""), 13, tint, TextAnchor.MiddleLeft));
-            row.Add(HudUi.Text(name, 13, tint, TextAnchor.MiddleLeft));
             row.Add(HudUi.Display("x" + count, 13, Color.white, TextAnchor.MiddleRight));
+            if (equippable)
+            {
+                row.pickingMode = PickingMode.Position;
+                ushort id = itemId;
+                row.RegisterCallback<ClickEvent>(_ => EquipSendSystem.Equip(id));
+            }
+            else row.pickingMode = PickingMode.Ignore;
             _invList.Add(row);
         }
 
@@ -817,6 +847,44 @@ namespace ProjectM.Client
             if (id == ResourceId.Biomass) return BioGreen;
             return new Color(0.85f, 0.85f, 0.9f);
         }
+        static bool IsEquippable(bool haveDb, ItemDatabase db, ushort id)
+        {
+            if (!haveDb || !db.Value.IsCreated) return false;
+            ref var b = ref db.Value.Value;
+            return b.TryGetItem(id, out var def) && def.EquipSlot < EquipSlotId.Count;
+        }
+
+        static string SlotName(byte slot)
+        {
+            switch (slot)
+            {
+                case EquipSlotId.Weapon: return "Weapon";
+                case EquipSlotId.Armor: return "Armor";
+                case EquipSlotId.Trinket: return "Trinket";
+                case EquipSlotId.Tool: return "Tool";
+                default: return "Slot " + slot;
+            }
+        }
+
+        void AddEquipRow(byte slot, string label, bool occupied)
+        {
+            var row = new VisualElement();
+            row.style.flexDirection = FlexDirection.Row;
+            row.style.justifyContent = Justify.SpaceBetween;
+            row.style.minWidth = 196;
+            row.style.marginTop = 2;
+            row.Add(HudUi.Text(label, 13, occupied ? AetherCyan : MenuUi.SubCol, TextAnchor.MiddleLeft));
+            if (occupied)
+            {
+                row.pickingMode = PickingMode.Position;
+                byte s = slot;
+                row.RegisterCallback<ClickEvent>(_ => EquipSendSystem.Unequip(s));
+                row.Add(HudUi.Text("unequip", 11, new Color(1f, 0.6f, 0.5f), TextAnchor.MiddleRight));
+            }
+            else row.pickingMode = PickingMode.Ignore;
+            _equipList.Add(row);
+        }
+
 
         static Color ResourceTint(byte resId)
             => resId == ResourceId.Aether ? AetherCyan : resId == ResourceId.Biomass ? BioGreen : OreAmber;

Assets/_Project/Scripts/Server/Economy/EquipSystem.cs

@@ -0,0 +1,160 @@
+using ProjectM.Simulation;
+using Unity.Burst;
+using Unity.Collections;
+using Unity.Entities;
+using Unity.NetCode;
+
+namespace ProjectM.Server
+{
+    /// <summary>
+    /// Server-authoritative equipment handler (<see cref="EquipRequest"/> / <see cref="UnequipRequest"/> RPCs).
+    /// Resolves the sender's player (SourceConnection -&gt; NetworkId -&gt; GhostOwner, the AbilityUpgradeSystem /
+    /// InventoryDepositSystem owner-map idiom) and applies the change IN-PLACE: moves the item between the
+    /// personal <see cref="InventorySlot"/> bag and the <see cref="EquipmentSlot"/> loadout (buffer index = slot),
+    /// sets <see cref="AbilityRef"/>.Id from the Weapon slot (restoring <see cref="DefaultAbility"/> on
+    /// weapon-unequip), and adds/strips the item's inline stat mods as <see cref="StatModifier"/>s tagged by a
+    /// per-slot SourceId (<c>Tuning.EquipSourceIdBase + slot</c>), stripped TARGET-AGNOSTICALLY via
+    /// <see cref="TimedModifierUtil.RemoveBySourceId"/>.
+    ///
+    /// Effects are EVENT-DRIVEN (applied once here): AbilityRef + StatModifier are [GhostField]s re-folded by the
+    /// predicted StatRecomputeSystem every tick and replicated to the owner, so the swap is prediction-correct
+    /// (DebugModifierInjectionSystem.CycleAbility is the precedent) and survives respawn (the entity persists).
+    /// Atomicity: an equip into an occupied slot verifies the bag can hold the swapped-out item BEFORE any
+    /// withdrawal and rejects otherwise — no item loss (the co-op-placement commit-in-place rule). Plain server
+    /// SimulationSystemGroup (NOT predicted -&gt; applied once, no rollback double-apply); only the request entity
+    /// destroy is deferred to the ECB.
+    /// </summary>
+    [BurstCompile]
+    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
+    public partial struct EquipSystem : ISystem
+    {
+        [BurstCompile]
+        public void OnCreate(ref SystemState state)
+        {
+            state.RequireForUpdate<ItemDatabase>();
+            var builder = new EntityQueryBuilder(Allocator.Temp)
+                .WithAny<EquipRequest, UnequipRequest>().WithAll<ReceiveRpcCommandRequest>();
+            state.RequireForUpdate(state.GetEntityQuery(builder));
+        }
+
+        [BurstCompile]
+        public void OnUpdate(ref SystemState state)
+        {
+            var itemDb = SystemAPI.GetSingleton<ItemDatabase>();
+
+            var playerByConn = new NativeHashMap<int, Entity>(8, Allocator.Temp);
+            foreach (var (owner, entity) in
+                     SystemAPI.Query<RefRO<GhostOwner>>()
+                         .WithAll<PlayerTag, InventorySlot, EquipmentSlot>().WithEntityAccess())
+                playerByConn[owner.ValueRO.NetworkId] = entity;
+
+            var ecb = new EntityCommandBuffer(Allocator.Temp);
+
+            foreach (var (request, receive, requestEntity) in
+                     SystemAPI.Query<RefRO<EquipRequest>, RefRO<ReceiveRpcCommandRequest>>().WithEntityAccess())
+            {
+                if (TryResolvePlayer(ref state, playerByConn, receive.ValueRO.SourceConnection, out var player))
+                    HandleEquip(ref state, itemDb, player, request.ValueRO.ItemId);
+                ecb.DestroyEntity(requestEntity);
+            }
+
+            foreach (var (request, receive, requestEntity) in
+                     SystemAPI.Query<RefRO<UnequipRequest>, RefRO<ReceiveRpcCommandRequest>>().WithEntityAccess())
+            {
+                if (TryResolvePlayer(ref state, playerByConn, receive.ValueRO.SourceConnection, out var player))
+                    HandleUnequip(ref state, itemDb, player, request.ValueRO.Slot);
+                ecb.DestroyEntity(requestEntity);
+            }
+
+            ecb.Playback(state.EntityManager);
+            playerByConn.Dispose();
+        }
+
+        static bool TryResolvePlayer(ref SystemState state, NativeHashMap<int, Entity> map, Entity conn, out Entity player)
+        {
+            player = Entity.Null;
+            return state.EntityManager.HasComponent<NetworkId>(conn)
+                && map.TryGetValue(state.EntityManager.GetComponentData<NetworkId>(conn).Value, out player);
+        }
+
+        static void HandleEquip(ref SystemState state, ItemDatabase itemDb, Entity player, ushort itemId)
+        {
+            ref var db = ref itemDb.Value.Value;
+            if (!db.TryGetItem(itemId, out var def)) return;
+            byte slot = def.EquipSlot;
+            if (slot >= EquipSlotId.Count) return; // not equippable (255 or out of range)
+
+            var bag = state.EntityManager.GetBuffer<InventorySlot>(player);
+            if (InventoryMath.CountOf(bag, itemId) < 1) return; // the sender isn't carrying it
+
+            var slots = state.EntityManager.GetBuffer<EquipmentSlot>(player);
+            ushort oldItem = slots[slot].ItemId;
+
+            // Atomicity: if the slot is occupied, the bag MUST be able to hold the swapped-out item before we
+            // touch anything; reject the whole equip otherwise so the old item is never lost.
+            if (oldItem != 0 && !InventoryMath.CanDeposit(bag, oldItem, 1, StackMaxOf(ref db, oldItem), Tuning.InventoryMaxSlots))
+                return;
+
+            // Commit in-place.
+            InventoryMath.Withdraw(bag, itemId, 1);
+            if (oldItem != 0)
+            {
+                InventoryMath.Deposit(bag, oldItem, 1, StackMaxOf(ref db, oldItem), Tuning.InventoryMaxSlots);
+                StripSlotEffects(ref state, player, slot);
+            }
+
+            slots[slot] = new EquipmentSlot { ItemId = itemId };
+            ApplySlotEffects(ref state, player, slot, def);
+        }
+
+        static void HandleUnequip(ref SystemState state, ItemDatabase itemDb, Entity player, byte slot)
+        {
+            if (slot >= EquipSlotId.Count) return;
+            ref var db = ref itemDb.Value.Value;
+
+            var slots = state.EntityManager.GetBuffer<EquipmentSlot>(player);
+            ushort item = slots[slot].ItemId;
+            if (item == 0) return; // nothing equipped
+
+            var bag = state.EntityManager.GetBuffer<InventorySlot>(player);
+            if (!InventoryMath.CanDeposit(bag, item, 1, StackMaxOf(ref db, item), Tuning.InventoryMaxSlots))
+                return; // bag full -> can't unequip (no item loss)
+
+            InventoryMath.Deposit(bag, item, 1, StackMaxOf(ref db, item), Tuning.InventoryMaxSlots);
+            slots[slot] = new EquipmentSlot { ItemId = 0 };
+            StripSlotEffects(ref state, player, slot);
+        }
+
+        static void ApplySlotEffects(ref SystemState state, Entity player, byte slot, ItemDefBlob def)
+        {
+            // Weapon slot drives the active ability (swaps prefab + base stats via StatRecomputeSystem).
+            if (slot == EquipSlotId.Weapon && def.GrantedAbilityId != 0)
+                state.EntityManager.SetComponentData(player, new AbilityRef { Id = def.GrantedAbilityId });
+
+            var mods = state.EntityManager.GetBuffer<StatModifier>(player);
+            uint sourceId = Tuning.EquipSourceIdBase + (uint)slot;
+            for (int i = 0; i < ItemDefBlob.MaxMods; i++)
+            {
+                var m = def.GetMod(i);
+                if (m.Target == 255) continue;
+                mods.Add(new StatModifier { Target = m.Target, Op = m.Op, Value = m.Value, SourceId = sourceId });
+            }
+        }
+
+        static void StripSlotEffects(ref SystemState state, Entity player, byte slot)
+        {
+            var mods = state.EntityManager.GetBuffer<StatModifier>(player);
+            TimedModifierUtil.RemoveBySourceId(mods, Tuning.EquipSourceIdBase + (uint)slot);
+
+            // Weapon slot: restore the unarmed/base ability.
+            if (slot == EquipSlotId.Weapon)
+            {
+                byte fallback = state.EntityManager.GetComponentData<DefaultAbility>(player).Id;
+                state.EntityManager.SetComponentData(player, new AbilityRef { Id = fallback });
+            }
+        }
+
+        static int StackMaxOf(ref ItemDatabaseBlob db, ushort itemId)
+            => db.TryGetItem(itemId, out var d) && d.StackMax > 0 ? d.StackMax : 1;
+    }
+}

Assets/_Project/Scripts/Server/Economy/EquipSystem.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 187144e115a815c4fae51eaa9e95012f

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

@@ -0,0 +1,17 @@
+using Unity.Entities;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// The player's "unarmed" / base ability id, baked from PlayerAuthoring.PrimaryAbility. Restored into
+    /// <see cref="AbilityRef"/>.Id by EquipSystem when a weapon is unequipped. NOT replicated (it never changes,
+    /// so a [GhostField] would waste snapshot bytes and there is no client consumer). AbilityRef itself cannot
+    /// serve double duty because EquipSystem overwrites AbilityRef.Id when a weapon is equipped — this preserves
+    /// the immutable default to fall back to. Server-read only.
+    /// </summary>
+    public struct DefaultAbility : IComponentData
+    {
+        /// <summary>The <see cref="AbilityId"/> (as a byte) the player fires with no weapon equipped.</summary>
+        public byte Id;
+    }
+}

Assets/_Project/Scripts/Simulation/Items/DefaultAbility.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 4c6831e7f8bb98d448917f88dcbe12db

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

@@ -0,0 +1,27 @@
+using Unity.NetCode;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// Client -&gt; server request to equip an item from the sender's personal inventory into the slot the
+    /// catalog assigns it (<see cref="ItemDefBlob.EquipSlot"/>). A one-off action, so it is an RPC (not a
+    /// per-tick predicted input); applied exactly once server-only in the plain SimulationSystemGroup. Carries
+    /// only the ItemId — the server derives the target slot from the catalog, so a client can't force a weapon
+    /// into the armor slot. Unconditional wire type (no #if); the server resolves the sender via SourceConnection.
+    /// </summary>
+    public struct EquipRequest : IRpcCommand
+    {
+        /// <summary>The inventory item to equip; the server resolves its slot + effects from the catalog.</summary>
+        public ushort ItemId;
+    }
+
+    /// <summary>
+    /// Client -&gt; server request to unequip whatever occupies <see cref="Slot"/> (an <see cref="EquipSlotId"/>),
+    /// returning the item to the personal inventory and stripping its effects. Unconditional wire type.
+    /// </summary>
+    public struct UnequipRequest : IRpcCommand
+    {
+        /// <summary>The <see cref="EquipSlotId"/> to clear.</summary>
+        public byte Slot;
+    }
+}

Assets/_Project/Scripts/Simulation/Items/EquipRequest.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: ad5475188aa05de45a231f937b19f069

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

@@ -0,0 +1,31 @@
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// Equipment-slot ids (a byte, not an enum, per the cross-assembly enum-in-Burst hazard). The player's
+    /// <see cref="EquipmentSlot"/> buffer holds one row PER slot in this fixed order (the buffer index IS the
+    /// slot), so these double as both the catalog's <see cref="ItemDefBlob.EquipSlot"/> value and the buffer
+    /// index. The Weapon slot grants its item's <see cref="ItemDefBlob.GrantedAbilityId"/> into AbilityRef;
+    /// every slot grants the item's inline stat mods. <see cref="Tool"/> is reserved for Phase 2 (tool-gated
+    /// harvesting). 255 = not equippable.
+    /// </summary>
+    public static class EquipSlotId
+    {
+        /// <summary>Weapon: grants the item's ability (AbilityRef.Id) + its stat mods.</summary>
+        public const byte Weapon = 0;
+
+        /// <summary>Armor: grants the item's stat mods.</summary>
+        public const byte Armor = 1;
+
+        /// <summary>Trinket: grants the item's stat mods.</summary>
+        public const byte Trinket = 2;
+
+        /// <summary>Tool (axe/pickaxe) — reserved for Phase 2 tool-gated harvesting.</summary>
+        public const byte Tool = 3;
+
+        /// <summary>Number of equipment slots (the baked <see cref="EquipmentSlot"/> buffer length).</summary>
+        public const byte Count = 4;
+
+        /// <summary>Sentinel: this item is not equippable.</summary>
+        public const byte None = 255;
+    }
+}

Assets/_Project/Scripts/Simulation/Items/EquipSlotId.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: ce8addc5ae6832a449d1b6ad459ab21a

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

@@ -0,0 +1,26 @@
+using Unity.Entities;
+using Unity.NetCode;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// One equipment slot on the player. The per-player buffer holds exactly <see cref="EquipSlotId.Count"/>
+    /// rows in fixed slot order (the buffer INDEX is the slot — Weapon=0/Armor=1/Trinket=2/Tool=3), so only the
+    /// equipped item id needs to replicate; there is no separate Slot field to desync. A [GhostField]
+    /// <see cref="SendToOwnerType.All"/> buffer (a <see cref="StatModifier"/>/<see cref="InventorySlot"/> twin)
+    /// so the owning client's HUD can show its loadout; the server is the SOLE writer (EquipSystem).
+    ///
+    /// The actual effects — AbilityRef.Id from the Weapon slot + StatModifiers per slot — are applied
+    /// EVENT-DRIVEN by EquipSystem (once per equip/unequip), NOT re-derived from this buffer each tick; this
+    /// buffer is the replicated record of WHAT is equipped (HUD-facing + persistence-ready), not the effect.
+    /// NOTE: adding this [GhostField] buffer changes the player ghost serialization hash → the player
+    /// prefab/subscene MUST be re-baked consistently in both worlds (see <see cref="InventorySlot"/>).
+    /// </summary>
+    [GhostComponent(OwnerSendType = SendToOwnerType.All)]
+    [InternalBufferCapacity(4)]
+    public struct EquipmentSlot : IBufferElementData
+    {
+        /// <summary>Item equipped in this slot (0 = empty). The buffer INDEX is the <see cref="EquipSlotId"/>.</summary>
+        [GhostField] public ushort ItemId;
+    }
+}

Assets/_Project/Scripts/Simulation/Items/EquipmentSlot.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: ac0f8812307d3ef43bbed63d1e3fb737

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)
         {

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

@@ -19,6 +19,20 @@ namespace ProjectM.Simulation
     /// is baked NOW because the project's progression axis is gear tiers, so Phase 2/3 tier gating is a
     /// content-only edit.
     /// </summary>
+    /// <summary>One stat-modifier grant on an equippable item, stored INLINE (NOT a nested BlobArray: a nested
+    /// BlobArray is a relative-offset pointer that corrupts the moment <see cref="ItemDatabaseBlob.TryGetItem"/>
+    /// returns the containing <see cref="ItemDefBlob"/> BY VALUE — the same copy hazard the class note warns about).
+    /// Target 255 = unused.</summary>
+    public struct ItemModSpec
+    {
+        /// <summary><see cref="StatTarget"/> as a byte; 255 = unused slot.</summary>
+        public byte Target;
+        /// <summary><see cref="ModOp"/> as a byte.</summary>
+        public byte Op;
+        /// <summary>Magnitude (flat amount or fractional percent).</summary>
+        public float Value;
+    }
+
     public struct ItemDefBlob
     {
         /// <summary>Stable item id (ushort; 1-3 reserved for the existing resources, keep stable for saves).</summary>
@@ -33,8 +47,32 @@ namespace ProjectM.Simulation
         /// <summary>Max units that stack in a single inventory slot (1 for non-stacking equipment).</summary>
         public int StackMax;
 
+        /// <summary>Equip slot (see <see cref="EquipSlotId"/>); 255 = not equippable.</summary>
+        public byte EquipSlot;
+
+        /// <summary>AbilityId granted when equipped in the Weapon slot (0 = none); the equip handler writes it into AbilityRef.Id.</summary>
+        public byte GrantedAbilityId;
+
+        /// <summary>Up to <see cref="MaxMods"/> INLINE stat-mod grants applied while equipped (Target 255 = unused). Inline, not a nested BlobArray.</summary>
+        public ItemModSpec Mod0, Mod1, Mod2, Mod3;
+
         /// <summary>Designer-facing display name (shown in the HUD inventory panel).</summary>
         public FixedString64Bytes Name;
+
+        /// <summary>Number of inline mod slots.</summary>
+        public const int MaxMods = 4;
+
+        /// <summary>Indexed access to the inline mod slots (returns a copy — safe, ItemModSpec holds no BlobArray).</summary>
+        public ItemModSpec GetMod(int i)
+        {
+            switch (i)
+            {
+                case 0: return Mod0;
+                case 1: return Mod1;
+                case 2: return Mod2;
+                default: return Mod3;
+            }
+        }
     }
 
     /// <summary>

Assets/_Project/Scripts/Simulation/Tuning.cs

@@ -64,5 +64,15 @@ namespace ProjectM.Simulation
 
         /// <summary>Default per-slot stack cap when an item has no ItemDatabase entry (the catalog is optional at runtime).</summary>
         public const int DefaultStackMax = 999;
+
+        // ---- Equipment stat-mod SourceIds (EquipSystem) ----
+        //   One DISTINCT sentinel per slot: slot i tags its mods with EquipSourceIdBase + i. All of a slot's
+        //   inline mods share that one id and are stripped target-agnostically via
+        //   TimedModifierUtil.RemoveBySourceId on unequip/swap. Full StatModifier SourceId map (keep DISJOINT):
+        //   0u = pickups + debug-injection; 0x00A0E711 = ability-damage upgrade; 0x00DEB061 = debug stat command;
+        //   0x00E91000.. = equipment (4 slots).
+
+        /// <summary>Base for per-slot equipment SourceIds; slot i tags its mods with <c>EquipSourceIdBase + i</c>.</summary>
+        public const uint EquipSourceIdBase = 0x00E91000u;
     }
 }

Assets/_Project/Subscenes/Gameplay.unity

@@ -1480,8 +1480,12 @@ MonoBehaviour:
   m_EditorClassIdentifier: ProjectM.Authoring::ProjectM.Authoring.ItemDatabaseAuthoring
   Items:
   - {fileID: 11400000, guid: 938a882b6fbd50d4c9a051ddabc5829b, type: 2}
+  - {fileID: 11400000, guid: b37686ead19d68d45b84e031bfe99f59, type: 2}
   - {fileID: 11400000, guid: a2a0e6d3ae0218d458d2b5305891ce89, type: 2}
+  - {fileID: 11400000, guid: 441dbd6676662a2459607f3b75ee821b, type: 2}
   - {fileID: 11400000, guid: 4ed399a329eb6d847921aef05bde213d, type: 2}
+  - {fileID: 11400000, guid: c09dc2c47feaa784486e21a3b7e4cb10, type: 2}
+  - {fileID: 11400000, guid: b69a26c8de798624b82e6799f8130291, type: 2}
   - {fileID: 11400000, guid: 31ec40cfc6e81ef4ab9bbce57a40621e, type: 2}
 --- !u!4 &722706770
 Transform: