fix(ui): match spellbook frame and tab alignment

docs/research/2026-07-15-retail-magic-ui-and-casting-pseudocode.md

@@ -221,6 +221,16 @@ UIElement_Text::OnSetAttribute @ 0x0046A640
         SetOneLine(value)
     // absent 0x20 therefore remains multi-line; do not force it true
 
+UIElement_Text::CalcJustification @ 0x00467260
+    available = max(scrollableExtent, surfaceExtent) - leadingMargin - trailingMargin
+    if justification is Center:
+        offset = available / 2 - contentExtent / 2
+    else if justification is Right or Bottom:
+        offset = available - contentExtent
+    else:
+        offset = 0
+    return leadingMargin + offset
+
 UIElement::SetState @ 0x00464E70
     next = desc.AccessStateDesc(stateId)
     if next != current:
@@ -245,6 +255,12 @@ before its retained children lets the center chrome overpaint the caption.
 This rule is derived structurally from `PassToChildren`, not from the two
 spellbook element ids.
 
+Layout `0x21000034` supplies the 300 by 600 content surface, including its tab
+bar and close control, but not the enclosing movable-window border. Production
+mounts it through the same shared retained nine-slice frame used by the
+Attributes/Skills window (`0x2100002E`). Treating the root as already framed
+removes the gold outer border.
+
 The Magic-combat favorite tab captions are authored text (`I` through `VIII`)
 and intentionally omit property `0x20`. Their small rectangles still render
 because retail begins with zero text margins. A generic four-pixel inset on

src/AcDream.App/UI/RetailUiRuntime.cs

@@ -764,7 +764,10 @@ public sealed class RetailUiRuntime : IDisposable
             new RetailWindowFrame.Options
             {
                 WindowName = WindowNames.Spellbook,
-                Chrome = RetailWindowChrome.Imported,
+                // LayoutDesc 0x21000034 is the 300x600 content surface. Like the
+                // Attributes/Skills window, retail supplies the outer gold frame
+                // through the shared window chrome rather than this root element.
+                Chrome = RetailWindowChrome.NineSlice,
                 Left = 18f,
                 Top = 18f,
                 Visible = false,

src/AcDream.App/UI/UiText.cs

@@ -166,6 +166,7 @@ public sealed class UiText : UiElement, IUiDatStateful
     private uint _activeRetailStateId = UiStateInfo.DirectStateId;
     private string _activeDatStateName = "";
     private bool _drawTextAfterChildren;
+    private bool _honorDatVerticalJustification;
 
     // ── Selection state ──────────────────────────────────────────────────
     private Pos? _selAnchor;   // where the drag started
@@ -206,6 +207,7 @@ public sealed class UiText : UiElement, IUiDatStateful
     internal void ConfigureDatState(ElementInfo info)
     {
         _datInfo = info;
+        _honorDatVerticalJustification = true;
         // Retail spellbook tabs are UIElement_Text parents whose Open/Closed
         // PassToChildren states drive three authored chrome pieces. In retail's
         // software surface those pieces form the tab background while the text
@@ -429,12 +431,18 @@ public sealed class UiText : UiElement, IUiDatStateful
             (int)MathF.Floor(innerH),
             preserveEnd: true);
 
-        // UiScrollable: ScrollY=0 is TOP/oldest, ScrollY=MaxScroll is BOTTOM/newest.
-        // Visual layout: newest at bottom → baseY = bottom - contentH (ScrollY at max).
-        // Invert: baseY = bottom - contentH + (MaxScroll - ScrollY).
-        // With _pinBottom: ScrollY=MaxScroll → baseY=bottom-contentH → last line ends at bottom. ✓
-        // Scrolled to top:  ScrollY=0 → baseY=bottom-contentH+MaxScroll=bottom-innerH=top. ✓
-        float baseY = bottom - contentH + (Scroll.MaxScroll - Scroll.ScrollY);
+        // Overflow keeps the UiScrollable convention: ScrollY=0 is TOP/oldest and
+        // ScrollY=MaxScroll is BOTTOM/newest. Fitting DAT-authored content instead
+        // uses retail CalcJustification (tabs center their one glyph line); synthesized
+        // transcript widgets retain the established bottom pin.
+        float baseY = ContentBaseY(
+            top,
+            bottom,
+            contentH,
+            Scroll.MaxScroll,
+            Scroll.ScrollY,
+            VerticalJustify,
+            _honorDatVerticalJustification);
         _lastBaseY = baseY;
 
         // Normalised selection span (start <= end), if any.
@@ -624,6 +632,35 @@ public sealed class UiText : UiElement, IUiDatStateful
             _               => (height - lineHeight) * 0.5f,   // Center (default)
         };
 
+    /// <summary>
+    /// Resolve the first line's Y coordinate for the normal multi-line path.
+    /// Retail <c>UIElement_Text::CalcJustification @ 0x00467260</c> applies the
+    /// authored vertical justification when the text content fits the surface;
+    /// overflow continues to use the scroll offset. Synthesized transcript widgets
+    /// retain the historical bottom-pinned behavior by passing
+    /// <paramref name="honorJustification"/> as <see langword="false"/>.
+    /// </summary>
+    public static float ContentBaseY(
+        float top,
+        float bottom,
+        float contentHeight,
+        float maxScroll,
+        float scrollY,
+        VJustify justification,
+        bool honorJustification)
+    {
+        float viewHeight = Math.Max(0f, bottom - top);
+        if (!honorJustification || contentHeight > viewHeight)
+            return bottom - contentHeight + (maxScroll - scrollY);
+
+        return justification switch
+        {
+            VJustify.Top => top,
+            VJustify.Bottom => bottom - contentHeight,
+            _ => top + (viewHeight - contentHeight) * 0.5f,
+        };
+    }
+
     /// <summary>Order two caret positions so the first is <= the second (by line,
     /// then column).</summary>
     public static (Pos start, Pos end) Order(Pos a, Pos b)

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

@@ -48,6 +48,9 @@ public sealed class SpellbookWindowControllerTests
 
         Assert.Equal("Spellbook", Assert.Single(spellTab.LinesProvider()).Text);
         Assert.Equal("Components", Assert.Single(componentTab.LinesProvider()).Text);
+        Assert.False(spellTab.OneLine);
+        Assert.True(spellTab.Centered);
+        Assert.Equal(VJustify.Center, spellTab.VerticalJustify);
         Assert.True(spellTab.DrawTextAfterChildren);
         Assert.True(componentTab.DrawTextAfterChildren);
 

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

@@ -227,4 +227,54 @@ public class UiTextTests
         Assert.Equal(yNoPad, yWithPad);   // Center is padding-independent
         Assert.Equal((40f - 12f) * 0.5f, yNoPad);
     }
+
+    [Theory]
+    [InlineData(VJustify.Top, 0f)]
+    [InlineData(VJustify.Center, 4.5f)]
+    [InlineData(VJustify.Bottom, 9f)]
+    public void ContentBaseY_FittingAuthoredText_UsesRetailVerticalJustification(
+        VJustify justification,
+        float expected)
+    {
+        float y = UiText.ContentBaseY(
+            top: 0f,
+            bottom: 25f,
+            contentHeight: 16f,
+            maxScroll: 0f,
+            scrollY: 0f,
+            justification,
+            honorJustification: true);
+
+        Assert.Equal(expected, y);
+    }
+
+    [Fact]
+    public void ContentBaseY_OverflowingAuthoredText_PreservesScrollPosition()
+    {
+        float y = UiText.ContentBaseY(
+            top: 0f,
+            bottom: 25f,
+            contentHeight: 64f,
+            maxScroll: 39f,
+            scrollY: 12f,
+            VJustify.Center,
+            honorJustification: true);
+
+        Assert.Equal(-12f, y);
+    }
+
+    [Fact]
+    public void ContentBaseY_SynthesizedText_RetainsBottomPinWhenContentFits()
+    {
+        float y = UiText.ContentBaseY(
+            top: 0f,
+            bottom: 25f,
+            contentHeight: 16f,
+            maxScroll: 0f,
+            scrollY: 0f,
+            VJustify.Center,
+            honorJustification: false);
+
+        Assert.Equal(9f, y);
+    }
 }