fix(D.5.1): occupancy-gated slot numbers (empty=0x1000005e bg digit) + bottom-right rect probe

FIX 1: UIElement_UIItem::SetShortcutNum (decomp 229481) has a three-way source
branch: occupied+peace -> 0x10000042 (peace digit set), occupied+war -> 0x10000043
(war digit set), empty (ItemId==0) -> 0x1000005e (background digit, stance-independent).
acdream previously only had the peace/war pair and drew them regardless of occupancy.

Changes:
- GameWindow.cs: read property 0x1000005e into toolbarEmptyDigits (no fallback;
  null is safe). Logs entry count. Passes emptyDigits to Bind. Adds [D.5.1 probe]
  block logging screen pos + size of 7 bottom-right element ids via ScreenPosition.
- ToolbarController.cs: adds _emptyDigits field, emptyDigits ctor+Bind param (null
  default). RestampShortcutNumbers sets cell.EmptyDigits. Comments cite decomp 229481.
- UiItemSlot.cs: adds EmptyDigits property + ActiveDigitArray() internal testable seam
  (occupied -> peace/war by stance; empty -> EmptyDigits). OnDraw uses it. Comment
  updated with three-way source table.
- Tests: 5 new UiItemSlotTests (ActiveDigitArray occupancy), 2 new
  ToolbarControllerTests (emptyDigits injection + null-safe).

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

src/AcDream.App/UI/Layout/ToolbarController.cs

@@ -55,12 +55,15 @@ public sealed class ToolbarController
     private readonly Action<uint> _useItem;                   // guid → fire UseObject
 
     // Digit sprite DID arrays for slot labels (top row, numbers 1-9).
-    // Peace set: property 0x10000042; war set: property 0x10000043.
     // Read from LayoutDesc 0x21000037, element 0x1000034A under composite 0x10000346.
     // Retail ref: UIElement_UIItem::SetShortcutNum (acclient_2013_pseudo_c.txt:229465);
     // gmToolbarUI::RecvNotice_SetCombatMode (196610-196621) re-stamps per stance.
+    // Occupancy branch (decomp 229481):
+    //   occupied → peace 0x10000042 / war 0x10000043 (split by stance)
+    //   empty    → background digit 0x1000005e (stance-independent)
     private uint[]? _peaceDigits;
     private uint[]? _warDigits;
+    private uint[]? _emptyDigits;
     private bool _peace = true;    // true = NonCombat (peace), false = any war stance
 
     private ToolbarController(
@@ -71,7 +74,8 @@ public sealed class ToolbarController
         Action<uint> useItem,
         CombatState? combatState,
         uint[]? peaceDigits,
-        uint[]? warDigits)
+        uint[]? warDigits,
+        uint[]? emptyDigits)
     {
         _repo = repo;
         _shortcuts = shortcuts;
@@ -79,6 +83,7 @@ public sealed class ToolbarController
         _useItem = useItem;
         _peaceDigits = peaceDigits;
         _warDigits   = warDigits;
+        _emptyDigits = emptyDigits;
 
         for (int i = 0; i < SlotIds.Length; i++)
         {
@@ -133,6 +138,12 @@ public sealed class ToolbarController
     /// UIElement_UIItem::SetShortcutNum (acclient_2013_pseudo_c.txt:229465).
     /// </param>
     /// <param name="warDigits">War-mode digit DID array (property 0x10000043, same element).</param>
+    /// <param name="emptyDigits">
+    /// Empty-slot background digit DID array (property 0x1000005e, stance-independent).
+    /// Used when a slot is EMPTY (ItemId == 0). Retail ref: UIElement_UIItem::SetShortcutNum
+    /// (decomp 229481) — else branch when m_elem_Icon->m_state == 0x1000001c (empty state).
+    /// Null if the dat lookup failed (empty slots draw no digit, which is safe).
+    /// </param>
     public static ToolbarController Bind(
         ImportedLayout layout,
         ItemRepository repo,
@@ -141,10 +152,11 @@ public sealed class ToolbarController
         Action<uint> useItem,
         CombatState? combatState = null,
         uint[]? peaceDigits = null,
-        uint[]? warDigits   = null)
+        uint[]? warDigits   = null,
+        uint[]? emptyDigits = null)
     {
         var c = new ToolbarController(layout, repo, shortcuts, iconIds, useItem, combatState,
-                                      peaceDigits, warDigits);
+                                      peaceDigits, warDigits, emptyDigits);
         c.Populate();
         return c;
     }
@@ -176,8 +188,9 @@ public sealed class ToolbarController
         }
 
         // Re-stamp slot number labels after any item change.
-        // Numbers show on ALL top-row slots regardless of item occupancy —
-        // the user's retail screenshot confirms numbers on empty top-row slots.
+        // Digit SPRITE SOURCE depends on occupancy (decomp UIElement_UIItem::SetShortcutNum:229481):
+        //   occupied → peace 0x10000042 / war 0x10000043; empty → background 0x1000005e.
+        // The digit is ALWAYS shown on top-row slots (SetVisible(1) at decomp 229511).
         RestampShortcutNumbers();
     }
 
@@ -215,12 +228,14 @@ public sealed class ToolbarController
 
     /// <summary>
     /// Push digit-array references and shortcut-number state into every slot cell.
-    /// Top row (indices 0–8): SetShortcutNum(i, _peace) — numbers 1–9 on ALL slots
-    /// including empty ones (confirmed from user's retail screenshot; the numbers are
-    /// slot LABELS, not item indicators).
+    /// Top row (indices 0–8): SetShortcutNum(i, _peace) — numbers 1–9 always shown
+    /// (the digit is ALWAYS visible, SetVisible(1) at decomp 229511; only the sprite
+    /// SOURCE differs by occupancy — see UIElement_UIItem::SetShortcutNum decomp 229481).
     /// Bottom row (indices 9–17): ClearShortcutNum() — retail shows no numbers there.
     /// Retail ref: UIElement_UIItem::SetShortcutNum (acclient_2013_pseudo_c.txt:229465);
     /// gmToolbarUI::RecvNotice_SetCombatMode (196610-196621).
+    /// Occupancy → source: occupied → peace 0x10000042 / war 0x10000043;
+    ///                      empty    → background 0x1000005e (decomp 229481/229493).
     /// </summary>
     private void RestampShortcutNumbers()
     {
@@ -230,6 +245,7 @@ public sealed class ToolbarController
             if (cell is null) continue;
             cell.PeaceDigits = _peaceDigits;
             cell.WarDigits   = _warDigits;
+            cell.EmptyDigits = _emptyDigits;
             if (i < 9)
                 cell.SetShortcutNum(i, _peace);   // top row: slot label digits 1–9 always shown
             else