Inventory: per-player items backbone (DR-026 Phase 0)

Data-driven ItemDatabase catalog + per-player replicated InventorySlot ([GhostField] OwnerSendType.All, a StatModifier twin). Harvest reroutes to the firing player's personal inventory (optional ComponentLookup<GhostOwner> in ResourceHarvestSystem; remainder/un-owned -> ledger); the G-key InventoryDepositRequest RPC moves the bag into the shared ledger the build economy spends. Catalog asset (Aether/Ore/Biomass + Stone Pickaxe) wired into the Gameplay subscene; read-only HUD inventory panel. ushort ItemId subsumes ResourceId; byte Category/Tier baked for gear-tier progression. Session-only (no SaveData bump).

Play-validated host+client: catalog baked into both worlds, the re-baked player ghost carries InventorySlot with a clean handshake, a server write replicates to the client owner, the deposit RPC round-trips, and the HUD renders catalog names. See DR-026.

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

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

@@ -0,0 +1,35 @@
+using Unity.Entities;
+using Unity.NetCode;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// One (item, count) row in a player's PERSONAL inventory. The per-player DynamicBuffer of these is the
+    /// server-authoritative source of what that player is carrying. A structural twin of
+    /// <see cref="StatModifier"/>: a [GhostField] buffer with <see cref="SendToOwnerType.All"/> so the owning
+    /// (predicting) client receives its own inventory — without it the owner, being the owner, would not get
+    /// the owner-typed buffer at all and the HUD would read empty. BOTH fields carry [GhostField]; the
+    /// [GhostComponent] attribute alone does NOT auto-replicate fields (an un-annotated field ships as a
+    /// silent zero), so the annotations mirror <see cref="StorageEntry"/> field-for-field.
+    ///
+    /// REPLICATION DISCIPLINE — the ONLY writers are server-only: <see cref="ProjectM.Server.ResourceHarvestSystem"/>
+    /// (harvest yield) and the deposit-to-base RPC handler, both in the plain server SimulationSystemGroup. So
+    /// there is no predicted-loop double-apply and the owner never mispredicts its inventory — it is a pure
+    /// server-authored snapshot. NEVER mutate this from a client predicted system (that would reintroduce a
+    /// double-apply / mispredict path). ItemId is the same opaque ushort id space as <see cref="StorageEntry"/>
+    /// and the <see cref="ItemDatabase"/> catalog.
+    ///
+    /// NOTE: adding this [GhostField] buffer CHANGES the player ghost serialization hash — the player prefab /
+    /// subscene MUST be re-baked (consistently in both worlds) or the connect handshake desyncs.
+    /// </summary>
+    [GhostComponent(OwnerSendType = SendToOwnerType.All)]
+    [InternalBufferCapacity(24)]
+    public struct InventorySlot : IBufferElementData
+    {
+        /// <summary>Item carried in this slot (0 = empty/unused; aligns with InventoryMath's 0-id no-op).</summary>
+        [GhostField] public ushort ItemId;
+
+        /// <summary>Quantity in this slot (bounded by the item's StackMax when deposited via InventoryMath).</summary>
+        [GhostField] public int Count;
+    }
+}