fix: complete retail parity stability pass

tests/AcDream.App.Tests/UI/UiMenuTests.cs

@@ -177,9 +177,11 @@ public class UiMenuTests
     }
 
     // ── G5 (vendor gate finding): Scrollable single-column popup ──────────────
-    // Retail's vendor category dropdown (LayoutDesc 0x21000043) is a SCROLLABLE
-    // single column with a docked scrollbar, not a column-major grid — see
-    // VendorUiController's "G5 correction" class-doc paragraph. Chat's own popup
+    // Retail's vendor category dropdown (LayoutDesc 0x21000043) is a scrollable
+    // single-column ListBox with a docked scrollbar, not a column-major grid.
+    // Its four-edge docking subsequently sizes the popup to content and property
+    // 0x79 hides that scrollbar when disabled; the fixed-viewport tests below
+    // retain coverage of UiMenu's actual overflow path. Chat's own popup
     // (exercised by every test above, Scrollable left at its false default) is
     // completely unaffected: it's a structurally different code path
     // (DrawGridPopup / the grid branch of OnEvent's MouseDown handling).
@@ -541,6 +543,45 @@ public class UiMenuTests
         Assert.False(menu.IsOpen);   // picking closes, same as every other path
     }
 
+    [Fact]
+    public void SizeToContent_WithAuthoredHideWhenDisabled_HidesTheScrollbarAndItsInput()
+    {
+        UiMenu menu = MakeScrollableMenu(3, sizeToContent: true);
+        menu.PopupScrollbarHideWhenDisabled = true;
+        Assert.Equal(menu.ColumnWidth + 2 * 5f, menu.PopupOuterWidth);
+        Assert.True(menu.OnEvent(new UiEvent(0, menu, UiEventType.MouseDown, 0, 10, 5))); // open
+
+        // Configure the exact content/view extents used by both drawing and
+        // pointer dispatch. Size-to-content makes them equal, so retail's
+        // authored scrollbar property 0x79 hides the entire sibling widget.
+        Assert.True(menu.OnEvent(new UiEvent(0, menu, UiEventType.Scroll, Data0: 0)));
+        Assert.False(menu.PopupScroll.HasOverflow);
+        Assert.False(menu.IsPopupScrollbarPresentationVisible);
+
+        // The old 16px sibling column is outside the popup now. A direct event
+        // at that old coordinate must not page/line scroll or leave an invisible
+        // control holding the popup open (UiRoot hit testing would not target the
+        // menu there at all because PopupOuterWidth has already collapsed).
+        float lx = 5f + menu.ColumnWidth + menu.ScrollbarWidth / 2f;
+        float ly = menu.Height + 5f + menu.RowHeight / 2f;
+        Assert.True(menu.OnEvent(new UiEvent(0, menu, UiEventType.MouseDown, 0, (int)lx, (int)ly)));
+        Assert.Equal(0, menu.PopupScroll.ScrollY);
+        Assert.False(menu.IsOpen);
+    }
+
+    [Fact]
+    public void FixedViewport_WithOverflow_KeepsHideWhenDisabledScrollbarVisible()
+    {
+        UiMenu menu = MakeScrollableMenu(18, sizeToContent: false);
+        menu.PopupScrollbarHideWhenDisabled = true;
+        Assert.True(menu.OnEvent(new UiEvent(0, menu, UiEventType.MouseDown, 0, 10, 5))); // open
+        Assert.True(menu.OnEvent(new UiEvent(0, menu, UiEventType.Scroll, Data0: 0)));
+
+        Assert.True(menu.PopupScroll.HasOverflow);
+        Assert.True(menu.IsPopupScrollbarPresentationVisible);
+        Assert.Equal(menu.ColumnWidth + menu.ScrollbarWidth + 2 * 5f, menu.PopupOuterWidth);
+    }
+
     [Fact]
     public void EmptyItems_ButtonClickDoesNotOpen()
     {
@@ -552,14 +593,16 @@ public class UiMenuTests
     }
 
     [Fact]
-    public void TextStyleDefaults_PreserveChatAndVendorBehavior()
+    public void MenuRetailBehaviorFlags_DefaultOff_ForMenusThatDoNotAuthorThem()
     {
-        // The three 2026-08-13 additions are opt-in: chat's gold left-aligned
-        // caption and vendor's fixed 6-row window are untouched by default.
+        // These are per-menu authored behaviors. Chat's grid popup keeps the
+        // generic left-aligned, non-resizing defaults; vendor opts into both
+        // content sizing and property-0x79 scrollbar hiding in its controller.
         var menu = new UiMenu();
         Assert.False(menu.ButtonTextCentered);
         Assert.False(menu.ItemTextCentered);
         Assert.False(menu.PopupSizeToContent);
+        Assert.False(menu.PopupScrollbarHideWhenDisabled);
     }
 
     /// <summary>