fix: complete retail parity stability pass

src/AcDream.App/UI/UiMenu.cs

@@ -85,21 +85,20 @@ public sealed class UiMenu : UiElement
     public float ColumnWidth   { get; set; } = 191f;  // dat item template W=191
 
     /// <summary>
-    /// G5 (vendor gate finding): retail's authored vendor category popup
+    /// Retail's authored vendor category popup
     /// (LayoutDesc <c>0x21000043</c>, root <c>0x1000034F</c>) pairs its
     /// ListBox (element <c>0x10000350</c>, type <c>0x5</c>) with a SIBLING
     /// <c>UIElement_Scrollbar</c> (element <c>0x10000351</c>, type <c>0xB</c>,
     /// 16px wide, docked immediately right of the list at x=100) — verified
-    /// via a live-dat scan (<c>tools/VendorLayoutScan</c>) against
-    /// <c>client_local_English.dat</c>: the ListBox reads a single-column
-    /// shape (attributes resolving to <c>m_nCols=1</c>/<c>m_nRows=6</c>) and
-    /// the row template (<c>0x10000352</c>) is 100×18 — a SCROLLABLE single
-    /// column with 6 visible rows, not our earlier column-major grid
-    /// approximation (which showed all 18 categories at once across 3
-    /// columns, never matching the retail screenshot's ~one-column-with-
-    /// scrollbar look). <see cref="RowsPerColumn"/> becomes the VISIBLE ROW
-    /// COUNT in this mode (still authored-driven — 108px ListBox height / 18px
-    /// row height = 6). Chat's own popup (LayoutDesc <c>0x21000006</c>) has
+    /// via installed-DAT inspection against <c>client_local_English.dat</c>.
+    /// The authored 100x108 ListBox starts with a six-row viewport, but retail
+    /// <c>UIElement_ListBox::UpdateLayout @0x0046e460</c> resizes its scrollable
+    /// content to the number of inserted categories. Because all four edges are
+    /// docked, message <c>0x32</c> reaches
+    /// <c>UIElement_Menu::RecalculatePopupSize @0x0046caf0</c> and grows or
+    /// shrinks the popup to that content. The sibling scrollbar authors property
+    /// <c>0x79=true</c>, so it disappears once the resized viewport fits the
+    /// content. Chat's own popup (LayoutDesc <c>0x21000006</c>) has
     /// NO sibling scrollbar element and keeps the class default false — the
     /// legacy column-major grid path below is untouched for it.
     /// </summary>
@@ -140,6 +139,24 @@ public sealed class UiMenu : UiElement
     public uint ScrollUpSprite { get; set; }
     public uint ScrollDownSprite { get; set; }
 
+    /// <summary>
+    /// Retail scrollbar property <c>0x79</c> for the popup's authored sibling
+    /// scrollbar. When the content fits and the scrollbar is therefore disabled,
+    /// hide the sibling completely: no chrome, pointer target, or reserved width.
+    /// Vendor popup element <c>0x10000351</c> authors this true. Retail owns a real
+    /// sibling widget and calls <c>SetVisible(false)</c> from
+    /// <c>UIElement_Scrollbar::UpdateLayout @0x004710d0</c>; this procedural popup
+    /// must also remove the sibling's width from its flattened geometry to produce
+    /// the same visible result.
+    /// </summary>
+    public bool PopupScrollbarHideWhenDisabled { get; set; }
+
+    /// <summary>Presentation projection shared by drawing and pointer dispatch.
+    /// Internal for the same focused-test purpose as
+    /// <see cref="UiScrollbar.IsPresentationVisible"/>.</summary>
+    internal bool IsPopupScrollbarPresentationVisible
+        => !PopupScrollbarHideWhenDisabled || PopupContentOverflows;
+
     private bool _draggingPopupThumb;
     private float _popupThumbDragOffset;
 
@@ -252,9 +269,8 @@ public sealed class UiMenu : UiElement
     /// popup ListBox (0x21000043/0x10000358) reads edges L=T=R=B=1
     /// (menuprobe3, <c>OptionsPanelLiveMountProbeTests</c>), so
     /// <see cref="AcDream.App.UI.Layout.ConfigOptionsPageController"/> sets
-    /// this true; chat's grid popup and vendor's shipped 6-row window keep
-    /// the class default false (vendor's authored ListBox is ALSO docked —
-    /// tracked as its own issue, not silently reworked here).
+    /// this true. Vendor's ListBox has the same four docked edges and therefore
+    /// enables it too; chat's grid popup keeps the class default false.
     /// When set, <see cref="RowsPerColumn"/> stops being the visible-window
     /// height and the popup shows every item with no scroll overflow.
     /// </summary>
@@ -333,12 +349,14 @@ public sealed class UiMenu : UiElement
 
     // Interior = the row content; Outer = interior + the 8-piece bevel ring.
     // Scrollable: always exactly one column (RowsPerColumn is the VISIBLE window,
-    // not a wrap threshold), widened by the docked scrollbar's own authored width.
+    // not a wrap threshold), widened by the docked scrollbar only while that
+    // sibling is presentation-visible. Retail property 0x79 removes a disabled
+    // scrollbar completely; keeping its width caused #386's empty placeholder.
     private int   ColumnCount => Scrollable
         ? 1
         : (Items.Count + RowsPerColumn - 1) / System.Math.Max(1, RowsPerColumn);
     private float InteriorW => Scrollable
-        ? ColumnWidth + ScrollbarWidth
+        ? ColumnWidth + EffectiveScrollbarWidth
         : ColumnCount * ColumnWidth;
 
     /// <summary>The popup's visible row count. Size-to-content (retail's
@@ -352,6 +370,15 @@ public sealed class UiMenu : UiElement
         ? System.Math.Max(1, Items.Count)
         : RowsPerColumn;
 
+    /// <summary>UiMenu rows have a fixed authored height, so this is the same
+    /// overflow decision <see cref="ConfigurePopupScroll"/> publishes to
+    /// <see cref="PopupScroll"/>, but is stable before the first draw/event has
+    /// configured that model.</summary>
+    private bool PopupContentOverflows => Items.Count > EffectiveVisibleRows;
+
+    private float EffectiveScrollbarWidth
+        => IsPopupScrollbarPresentationVisible ? ScrollbarWidth : 0f;
+
     private float InteriorH => EffectiveVisibleRows * RowHeight;
     private float OuterW => InteriorW + 2 * Border;
     private float OuterH => InteriorH + 2 * Border;
@@ -362,6 +389,11 @@ public sealed class UiMenu : UiElement
     /// a full render pass.</summary>
     public float PopupOuterHeight => OuterH;
 
+    /// <summary>The popup's outer (bevel-inclusive) width. Exposed alongside
+    /// <see cref="PopupOuterHeight"/> so the retail hide-disabled scrollbar rule
+    /// can be pinned without a GPU render harness.</summary>
+    public float PopupOuterWidth => OuterW;
+
     /// <summary>
     /// G7 (vendor gate finding, item 2 — popup direction): port of retail
     /// <c>UIElement_Menu::Open</c> (pc:120210-120252, <c>0x0046cc30</c>)'s Y placement:
@@ -558,10 +590,11 @@ public sealed class UiMenu : UiElement
     /// <summary>
     /// G5: single-column popup with a docked scrollbar — port of the vendor category
     /// dropdown's authored shape (LayoutDesc <c>0x21000043</c>, see <see cref="Scrollable"/>'s
-    /// doc comment). Draws exactly <see cref="RowsPerColumn"/> rows (the authored visible
-    /// window), sliced from <see cref="Items"/> starting at <see cref="VisibleTopRow"/>, plus
-    /// the scrollbar chrome using the SAME thumb geometry <see cref="UiScrollbar"/> itself
-    /// uses (<see cref="UiScrollbar.ThumbRect"/>).
+    /// doc comment). Draws <see cref="EffectiveVisibleRows"/> rows, sliced from
+    /// <see cref="Items"/> starting at <see cref="VisibleTopRow"/>, plus the scrollbar
+    /// chrome when its authored disabled-presentation rule allows it. Thumb geometry
+    /// is the same helper <see cref="UiScrollbar"/> itself uses
+    /// (<see cref="UiScrollbar.ThumbRect"/>).
     /// </summary>
     private void DrawScrollablePopup(UiRenderContext ctx, Func<uint, (uint tex, int w, int h)> resolve)
     {
@@ -602,9 +635,9 @@ public sealed class UiMenu : UiElement
     {
         int lineHeight = System.Math.Max(1, (int)MathF.Round(RowHeight));
         PopupScroll.LineHeight = lineHeight;
-        // Size-to-content: view == content, so HasOverflow is false and the
-        // scrollbar draws its chrome with no thumb (retail's authored
-        // scrollbar sibling stretches with the docked popup the same way).
+        // Size-to-content: view == content, so HasOverflow is false. Whether
+        // the disabled scrollbar remains visible is its authored 0x79 property,
+        // projected by IsPopupScrollbarPresentationVisible.
         PopupScroll.SetExtents(Items.Count * lineHeight, EffectiveVisibleRows * lineHeight);
     }
 
@@ -625,6 +658,8 @@ public sealed class UiMenu : UiElement
     private void DrawPopupScrollbar(
         UiRenderContext ctx, Func<uint, (uint tex, int w, int h)> resolve, float x, float y)
     {
+        if (!IsPopupScrollbarPresentationVisible) return;
+
         DrawSprite(ctx, resolve, ScrollTrackSprite, x, y, ScrollbarWidth, InteriorH);
 
         float decExtent = System.Math.Clamp(ScrollButtonExtent, 0f, InteriorH);
@@ -801,7 +836,9 @@ public sealed class UiMenu : UiElement
         }
 
         float scrollbarX = ColumnWidth;
-        if (ix >= scrollbarX && ix < scrollbarX + ScrollbarWidth && iy >= 0 && iy < InteriorH)
+        if (IsPopupScrollbarPresentationVisible
+            && ix >= scrollbarX && ix < scrollbarX + ScrollbarWidth
+            && iy >= 0 && iy < InteriorH)
         {
             ConfigurePopupScroll();
             float decExtent = System.Math.Clamp(ScrollButtonExtent, 0f, InteriorH);