fix(ui): #372 — Options tabs no longer blank; UiTemplateListBox viewport fills its ListBox

ROOT CAUSE (proven, not guessed): the lazily-created row viewport was
constructed 0x0 with Left|Top|Right|Bottom fill-anchors. Its first
ApplyAnchor captured mR = parentW - (0+0) = parentW, so
ComputeAnchoredRect's l&&r branch (w = parentW - mR - mL) kept it 0x0
forever. A 0-tall viewport makes UiScrollablePanel.LayoutScrollableChildren
cull every row, so Character/Chat/Config rendered blank while Gameplay
(no viewport — authored static children sized at Build) worked. This is
the exact Gameplay-vs-rest split the user's first connected gate found.

FIX: seed the viewport to the ListBox's current extent at creation, so the
fill-anchor baseline is mR = parentW - parentW = 0 and the viewport tracks
the parent. The ListBox is a static dat child sized at Build, so its extent
is authored by the time the viewport is lazily created during Bind.
Dormancy preserved — the viewport is still created only on the first row.

Reproduced RED then GREEN by UiTemplateListBoxViewportTests (viewport fills;
rows stay visible after the anchor+cull layout pass) — the layout path the
whole fixture conformance suite structurally never drove, which is why
every OP2-OP6 test was green over a live-only blank-tab failure. Full
Release suite 13,131 / 4 skips / 0 failed.

Still owed (NOT fixed here, no evidence yet): the 'only Exit Game worked'
Gameplay-buttons observation needs a re-gate (two buttons are correctly
INERT; the other four have dialog/chat effects that may have gone
unnoticed); and the 13 ID_ChatOption_TextFilter_* labels fail to resolve
(blank captions, behaviour unaffected). See #372.

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

docs/ISSUES.md

@@ -26,7 +26,44 @@ What does NOT go here:
 
 ## #372 — Options panel: Character/Chat/Config tabs render BLANK on screen and most Gameplay buttons do nothing (connected-gate failure)
 
-**Status:** OPEN — filed 2026-08-11 at Campaign OP's first connected gate
+**Status:** BLANK-TABS ROOT-CAUSED + FIXED (`c3ed32fb` probe, fix this
+commit); the Gameplay-buttons observation still needs a re-gate. Filed
+2026-08-11 at Campaign OP's first connected gate.
+
+**ROOT CAUSE (blank tabs) — found + fixed.** `UiTemplateListBox` creates its
+row viewport lazily (post-Build, during a page controller's `Bind`) at
+**0×0** with `Left|Top|Right|Bottom` fill-anchors. The anchor system captures
+its baseline from that 0-size rect (`mR = parentW − (Left+Width) = parentW`),
+and `UiElement.ComputeAnchoredRect`'s left+right branch then yields
+`w = parentW − mR − mL = 0` (and `h = 0`) **permanently**. A 0-tall viewport
+makes `UiScrollablePanel.LayoutScrollableChildren` cull every row
+(`top + height ≤ Height` is false for any real row at Height 0), so every
+ListBox-backed tab (Character/Chat/Config) draws empty. Gameplay works
+because it has no viewport — its buttons are authored static children sized
+at Build, so they never hit the lazy-0×0 path. **Fix:** seed the viewport to
+the ListBox's current extent at creation (`UiTemplateListBox.cs` Viewport
+getter), so the fill-anchor baseline is `mR = parentW − parentW = 0` and the
+viewport tracks the ListBox. Regressed by
+`tests/AcDream.App.Tests/UI/UiTemplateListBoxViewportTests.cs` (RED→GREEN)
+and the live-DAT mount probe. Every fixture conformance test stayed green
+throughout — the false-negative class this issue documents — so the
+regression test drives the anchor+cull layout path the suite never did.
+
+**Still owed — the Gameplay-buttons half is NOT root-caused.** Of the seven
+buttons the user found only Exit Game acting. Two (Configure Keyboard,
+In-Game Help) are correctly INERT. The other four (Exit-to-CharSel confirm
+dialog, Use-Mouse-Turning chat lines, Urgent Assistance / Report Abuse
+failure text) have effects that may have gone unnoticed rather than failed —
+no evidence either way yet. Needs a re-gate observation (per-button: does a
+click produce ANY visible response) before investigating; do not guess-fix.
+Separately, the live log showed all 13 `ID_ChatOption_TextFilter_*` Chat-tab
+filter labels failing to resolve from string table `0x23000003` (rows render
+blank-captioned by the honest-fallback path; masks/behaviour unaffected) — a
+minor label-resolution bug to fix (wrong table id or key spelling for that
+family), tracked here until split out.
+
+<!-- original filing -->
+**(filed OPEN)** — 2026-08-11 at Campaign OP's first connected gate
 (`ACDREAM_RETAIL_UI=1`, live ACE). The user found: opening the Options panel
 (F11/toolbar) shows the Gameplay tab, but switching to Character/Chat/Config
 shows a BLANK page, and of the seven Gameplay buttons only **Exit Game**

src/AcDream.App/UI/UiTemplateListBox.cs

@@ -144,16 +144,37 @@ public sealed class UiTemplateListBox : UiDatElement
     /// <summary>Retail ListBox rows never come from static dat children — see class doc.</summary>
     public override bool ConsumesDatChildren => true;
 
+    /// <summary>The lazily-created row viewport, or null before the first row is added.
+    /// Exposed for #372's regression test (the viewport must fill this ListBox, not
+    /// collapse to 0×0).</summary>
+    internal UiScrollablePanel? ViewportForTest => _viewport;
+
     private UiScrollablePanel Viewport
     {
         get
         {
             if (_viewport is null)
             {
+                // #372: the viewport MUST start filling this ListBox. It is created
+                // lazily (post-Build, during a page controller's Bind), so it misses
+                // the Build-time sizing that authored static children get. With
+                // Left|Top|Right|Bottom fill-anchors but a 0×0 initial rect, the
+                // anchor system captures a degenerate baseline (mR = parentW - (0+0)
+                // = parentW) and ComputeAnchoredRect then keeps it 0×0 forever
+                // (w = parentW - mR - mL = 0) — a 0-tall viewport makes
+                // UiScrollablePanel.LayoutScrollableChildren cull every row, so every
+                // ListBox-backed Options tab renders BLANK (Gameplay, which has no
+                // viewport, was the only tab that worked). Seeding the viewport to
+                // this ListBox's current size makes the fill-anchor baseline correct
+                // (mR = parentW - (0 + parentW) = 0) and self-maintaining as the
+                // ListBox re-anchors each frame. The ListBox is a static dat child
+                // sized at Build, so its extent is already authored here.
                 _viewport = new UiScrollablePanel
                 {
                     Anchors = AnchorEdges.Left | AnchorEdges.Top | AnchorEdges.Right | AnchorEdges.Bottom,
                     LineHeight = _pendingLineHeight,
+                    Width = Width,
+                    Height = Height,
                 };
                 base.AddChild(_viewport);
             }

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

@@ -0,0 +1,79 @@
+using AcDream.App.UI;
+using AcDream.App.UI.Layout;
+
+namespace AcDream.App.Tests.UI;
+
+/// <summary>
+/// #372 regression: the Options panel's Character/Chat/Config tabs rendered
+/// BLANK at the first connected gate while Gameplay (which has no ListBox)
+/// worked. Root cause: <see cref="UiTemplateListBox"/> creates its row
+/// viewport at 0×0 with Left|Top|Right|Bottom fill-anchors; the anchor
+/// baseline captured from that 0-size rect makes
+/// <c>ComputeAnchoredRect</c> keep it 0×0 forever (mR=parentW, so
+/// w=parentW-mR-mL=0), and <see cref="UiScrollablePanel.LayoutScrollableChildren"/>
+/// then culls every row (top+height ≤ 0 is false). These tests pin that the
+/// viewport fills its ListBox and the rows stay visible after a layout pass.
+/// </summary>
+public sealed class UiTemplateListBoxViewportTests
+{
+    private static UiTemplateListBox MakeListBox(float width, float height)
+    {
+        // A ListBox element authoring one template entry, sized like the
+        // Options-panel Character ListBox (0x100001FA, 276×560 authored).
+        var info = new ElementInfo { Id = 0x100001FAu, Type = 5u };
+        var box = new UiTemplateListBox(
+            info,
+            _ => (0u, 0, 0),
+            new[] { new UiTemplateListEntry(0x2100002Bu, 0x10000218u) },
+            scrollbarElementId: 0x100001FBu)
+        {
+            Width = width,
+            Height = height,
+        };
+        return box;
+    }
+
+    [Fact]
+    public void Viewport_FillsTheListBox_NotCollapsedToZero()
+    {
+        var box = MakeListBox(276f, 560f);
+        // Add a couple of rows via the prebuilt path (no DAT needed).
+        box.AddPrebuiltRow(new UiText { Width = 260f, Height = 20f });
+        box.AddPrebuiltRow(new UiText { Width = 260f, Height = 20f });
+
+        UiScrollablePanel? viewport = box.ViewportForTest;
+        Assert.NotNull(viewport);
+
+        // Drive the per-frame layout the draw traversal runs: the parent
+        // ListBox re-anchors its children (UiElement.DrawSelfAndChildren
+        // line ~500), sizing the fill-anchored viewport.
+        viewport!.ApplyAnchor(box.Width, box.Height);
+
+        // The whole point of #372: the viewport must FILL the ListBox, not
+        // collapse. Pre-fix this was 0×0.
+        Assert.Equal(276f, viewport.Width, 3);
+        Assert.Equal(560f, viewport.Height, 3);
+    }
+
+    [Fact]
+    public void Rows_StayVisible_AfterLayout_WhenTheyFitTheViewport()
+    {
+        var box = MakeListBox(276f, 560f);
+        var row0 = new UiText { Width = 260f, Height = 20f };
+        var row1 = new UiText { Width = 260f, Height = 20f };
+        var row2 = new UiText { Width = 260f, Height = 20f };
+        box.AddPrebuiltRow(row0);
+        box.AddPrebuiltRow(row1);
+        box.AddPrebuiltRow(row2);
+
+        UiScrollablePanel viewport = box.ViewportForTest!;
+        viewport.ApplyAnchor(box.Width, box.Height); // size the viewport
+        viewport.LayoutScrollableChildren();          // the cull pass (runs each OnDraw)
+
+        // All three rows sit at y 0/20/40 inside a 560px viewport → visible.
+        // Pre-fix the viewport was 0px tall and every row was culled → blank tab.
+        Assert.True(row0.Visible, "row 0 culled — the #372 blank-tab bug");
+        Assert.True(row1.Visible, "row 1 culled — the #372 blank-tab bug");
+        Assert.True(row2.Visible, "row 2 culled — the #372 blank-tab bug");
+    }
+}