feat(D.2b): ClientObjectTable optimistic move + confirm/rollback for inventory drag

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

src/AcDream.Core/Items/ClientObjectTable.cs

@@ -44,6 +44,11 @@ public sealed class ClientObjectTable
     private readonly ConcurrentDictionary<uint, Container> _containers = new();
     private readonly Dictionary<uint, List<uint>> _containerIndex = new();
 
+    // B-Drag: pre-move snapshots for optimistic inventory moves. itemId → (container, slot) BEFORE
+    // the optimistic MoveItem; restored by RollbackMove on InventoryServerSaveFailed (0x00A0),
+    // cleared by ConfirmMove on the InventoryPutObjInContainer (0x0022) echo.
+    private readonly Dictionary<uint, (uint container, int slot)> _pendingMoves = new();
+
     /// <summary>Fires when an object is first added to the session.</summary>
     public event Action<ClientObject>? ObjectAdded;
 
@@ -130,6 +135,33 @@ public sealed class ClientObjectTable
         return true;
     }
 
+    /// <summary>
+    /// Optimistic (instant) move: snapshot the item's current (ContainerId, ContainerSlot) the FIRST
+    /// time it moves, then <see cref="MoveItem"/> (immediate repaint via ObjectMoved). The wire
+    /// PutItemInContainer is sent by the caller; <see cref="ConfirmMove"/>/<see cref="RollbackMove"/>
+    /// reconcile against the server. Retail: local ItemList_InsertItem + ServerSaysMoveItem reconcile.
+    /// </summary>
+    public bool MoveItemOptimistic(uint itemId, uint newContainerId, int newSlot)
+    {
+        if (!_objects.TryGetValue(itemId, out var item)) return false;
+        if (!_pendingMoves.ContainsKey(itemId))
+            _pendingMoves[itemId] = (item.ContainerId, item.ContainerSlot);   // snapshot the ORIGINAL once
+        return MoveItem(itemId, newContainerId, newSlot);
+    }
+
+    /// <summary>The server confirmed the move (InventoryPutObjInContainer 0x0022 echo) — drop the
+    /// pending snapshot. No-op for a server-initiated move we never tracked.</summary>
+    public void ConfirmMove(uint itemId) => _pendingMoves.Remove(itemId);
+
+    /// <summary>The server rejected the move (InventoryServerSaveFailed 0x00A0) — restore the item to
+    /// its pre-move (container, slot) and drop the snapshot. False if nothing was pending.</summary>
+    public bool RollbackMove(uint itemId)
+    {
+        if (!_pendingMoves.TryGetValue(itemId, out var pre)) return false;
+        _pendingMoves.Remove(itemId);
+        return MoveItem(itemId, pre.container, pre.slot);
+    }
+
     /// <summary>
     /// Handle a server-driven remove (destroyed item, dropped into 3D
     /// space, stolen, etc).