fix(ui): restore retail magic shortcut bar

Port the retail horizontal ItemList empty-slot padding and share UIItem shortcut-number graphics with the status toolbar. Preserve all authored face children on compound DAT buttons so the three-piece Cast control reflows and renders as one complete button.

Co-authored-by: OpenAI Codex <codex@openai.com>

src/AcDream.App/UI/UiItemList.cs

@@ -82,6 +82,10 @@ public sealed class UiItemList : UiElement
 
     public int GetNumUIItems() => _cells.Count;
 
+    /// <summary>Returns this cell's current retained-list position, matching
+    /// UIElement_ListBox::WhatNum. -1 means the cell is not owned by this list.</summary>
+    public int IndexOf(UiItemSlot cell) => _cells.IndexOf(cell);
+
     public UiItemSlot? GetItem(int index)
         => index >= 0 && index < _cells.Count ? _cells[index] : null;
 
@@ -128,6 +132,24 @@ public sealed class UiItemList : UiElement
     /// <summary>Fixed cell height in grid mode (pairs with CellWidth).</summary>
     public float CellHeight { get; set; }
 
+    /// <summary>
+    /// Lay cells left-to-right in one row. Retail favorite spell lists use the
+    /// horizontal UpdateEmptySlots branch (row-count attribute 0x5F is -1), so
+    /// the number of visible cells is determined by width rather than the nine
+    /// shortcut-number overlays.
+    /// </summary>
+    public bool SingleRow { get; set; }
+
+    /// <summary>
+    /// Maintain a tail of empty UIItems that fills the visible horizontal extent.
+    /// Port of UIElement_ItemList::UpdateEmptySlots @ 0x004E3700.
+    /// </summary>
+    public bool FillVisibleEmptySlots { get; set; }
+
+    /// <summary>Creates an empty cell for <see cref="FillVisibleEmptySlots"/>.
+    /// Null uses a plain physical UiItemSlot.</summary>
+    public Func<UiItemSlot>? EmptySlotFactory { get; set; }
+
     /// <summary>Whole rows needed for <paramref name="cellCount"/> cells in a grid of
     /// <paramref name="columns"/> columns.</summary>
     public static int RowCount(int cellCount, int columns)
@@ -177,7 +199,11 @@ public sealed class UiItemList : UiElement
             return;
         }
 
-        int cols = Columns < 1 ? 1 : Columns;
+        UpdateEmptySlots();
+
+        int cols = SingleRow
+            ? Math.Max(1, _cells.Count)
+            : Columns < 1 ? 1 : Columns;
         int cellH = (int)MathF.Round(CellHeight);
 
         // Drive the shared scroll model from the current geometry, then re-clamp the offset to
@@ -201,6 +227,35 @@ public sealed class UiItemList : UiElement
         }
     }
 
+    /// <summary>
+    /// Retail's horizontal branch pads to floor(listWidth / cellWidth), and when
+    /// the viewport shrinks removes only empty cells from the tail. Occupied cells
+    /// are never discarded merely because they extend beyond the viewport.
+    /// </summary>
+    private void UpdateEmptySlots()
+    {
+        if (!FillVisibleEmptySlots || !SingleRow || CellWidth <= 0f)
+            return;
+
+        int visibleCellCount = Math.Max(0, (int)MathF.Floor(Width / CellWidth));
+        while (_cells.Count < visibleCellCount)
+        {
+            UiItemSlot cell = EmptySlotFactory?.Invoke() ?? new UiItemSlot();
+            cell.SpriteResolve ??= SpriteResolve;
+            if (_cellEmptySprite != 0) cell.EmptySprite = _cellEmptySprite;
+            cell.Anchors = AnchorEdges.None;
+            _cells.Add(cell);
+            AddChild(cell);
+        }
+
+        while (_cells.Count > visibleCellCount && _cells[^1].IsEmptySlot)
+        {
+            UiItemSlot cell = _cells[^1];
+            _cells.RemoveAt(_cells.Count - 1);
+            RemoveChild(cell);
+        }
+    }
+
     protected override bool ClipsChildren => CellWidth > 0f;
 
     public void Flush()