fix: trade gate round 4 - "The trade has been cancelled." + retail's

staged-item trading marker

- Cancel text: ClientTradeSystem::Handle_Trade__Recv_CloseTrade
  @0x0056DE30 shows "The trade has been cancelled." UNCONDITIONALLY
  (every close reason) as 0x1A ClientLocal - the yellow top-center
  SpewBox line. Wired at the router's onTradeClose beside ApplyClose;
  the string lives in ClientTextRefusals with its citation.
- Staged-item marker: retail's mechanism decoded end-to-end - the
  UIItem prototype (catalog 0x21000037) authors overlay child
  0x10000438 (sprite 0x06001DAE, the green frame + corner trade icon),
  bound @0x004E18FC and SetVisible(tradeState != 0) @0x004E2420;
  gmSecureTradeUI::AddItem @0x004CA801 sets
  ACCWeenieObject::SetTradeState(1) on YOUR staged items. Ported as:
  UiItemSlot.ShowTradeOverlay + TradeOverlaySprite (drawn over the
  icon), set on the trade window's self-grid cells; and
  RuntimeTradeState now borrows the canonical object table and
  maintains ClientObject.TradeState (1 at stage, 0 at remove/failure/
  reset/close/clear) - which also brings the ALREADY-PORTED placement
  policy's "You cannot move an item while it is being traded" refusal
  to life (its input field previously had no live producer).

Runtime 1,626, App 4,992/3 - green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/UI/Layout/PowerbarLayoutProbeTests.cs

@@ -141,6 +141,29 @@ public sealed class PowerbarLayoutProbeTests
         }
     }
 
+    /// <summary>2026-08-14 trade gate round 4: dump the shared UIItem
+    /// catalog 0x21000037 tree — find the trading-overlay art (retail marks
+    /// staged cells via ACCWeenieObject::SetTradeState @ 0x004CA801; the
+    /// UIItem draw reads it).</summary>
+    [Fact]
+    public void ProbeUiItemCatalog()
+    {
+        if (Environment.GetEnvironmentVariable("ACDREAM_PROBE_POWERBAR") != "1")
+            return;
+
+        var datDir = Environment.GetEnvironmentVariable("ACDREAM_DAT_DIR")
+            ?? Path.Combine(
+                Environment.GetFolderPath(Environment.SpecialFolder.UserProfile),
+                "Documents",
+                "Asheron's Call");
+        using var dats = new DatCollection(datDir, DatAccessType.Read);
+        var strings = new DatStringResolver(dats);
+
+        ElementInfo? root = LayoutImporter.ImportInfos(dats, 0x21000037u);
+        Assert.NotNull(root);
+        DumpElement(strings, root!, 0);
+    }
+
     private static ElementInfo? FindById(ElementInfo element, uint id)
     {
         if (element.Id == id) return element;
@@ -169,10 +192,16 @@ public sealed class PowerbarLayoutProbeTests
     private static void DumpElement(DatStringResolver strings, ElementInfo e, int depth)
     {
         string indent = new(' ', depth * 2);
+        string media = string.Join(
+            " ",
+            e.StateMedia
+                .OrderBy(static pair => pair.Key, StringComparer.Ordinal)
+                .Select(static pair => $"'{pair.Key}'=0x{pair.Value.File:X8}"));
         Console.WriteLine(
             $"[pbprobe] {indent}0x{e.Id:X8} type={e.Type} ({e.X},{e.Y} {e.Width}x{e.Height}) "
             + $"defaultState=0x{e.DefaultStateId:X8}('{e.DefaultStateName}') states={e.States.Count} "
-            + $"hjustify={e.HJustify} fontColor={(e.FontColor is { } fc ? fc.ToString() : "none")}");
+            + $"hjustify={e.HJustify} fontColor={(e.FontColor is { } fc ? fc.ToString() : "none")} "
+            + $"media[{media}]");
         foreach (var (stateId, state) in e.States)
         {
             string text = "";