feat(D.2b): UiScrollbar (Type 11) — promote the generic chat scrollbar (widget-generalization Task 2)

- git mv UiChatScrollbar.cs → UiScrollbar.cs; rename class + update doc summary to
  "Generic scrollbar. Ports retail UIElement_Scrollbar (RegisterElementClass(0xb) @
  acclient_2013_pseudo_c.txt:124137); thumb size = trackLen * ThumbRatio (min 8px); step ±1 line."
- git mv UiChatScrollbarTests.cs → UiScrollbarTests.cs; rename test class + replace
  every UiChatScrollbar reference with UiScrollbar (bodies unchanged).
- DatWidgetFactory: register Type 11 → new UiScrollbar() before the _ fallback case.
- ChatWindowController: change Scrollbar property type to UiScrollbar; replace the old
  "construct-remove-add" block with a "find factory-built UiScrollbar and bind in place"
  block (no RemoveChild/AddChild); keep `var track` assignment in scope so the Max/Min
  block's track.Left/track.Width reads still compile against UiElement?.
- AP-41 divergence register: update file:line to UiScrollbar.cs:35; narrow wording to
  "fallback only — single-tile drawn only when cap ids are unset; the chat controller
  passes all three cap ids so the 3-slice path is the active code path."
- Update inline UiChatScrollbar doc-comment references in UiScrollable.cs + UiChatView.cs.
- Full suite: 399 passed, 2 skipped (dat/tower fixture skips), 0 failed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/architecture/retail-divergence-register.md

@@ -138,7 +138,7 @@ accepted-divergence entries (#96, #49, #50).
 | AP-38 | Chat transcript renders pre-split `ChatLog` lines 1:1; no in-element word-wrap at the panel's current pixel width | `src/AcDream.App/UI/UiChatView.cs` | Retail does in-element wrap via `UIElement_Text::SizeToFit`; our pre-split lines are always shorter than 440 px in practice; a line that overflows clips at the edge rather than wrapping | Very long server system messages (server shutdowns, broadcast announcements) clip rather than wrapping — no information loss, just visual truncation | `UIElement_Text::SizeToFit` @0x467980; `gmMainChatUI` layout |
 | AP-39 | Chat lines carry one color per `ChatKind` (per-line solid color); retail `UIElement_Text` supports per-glyph styled runs (bold, different hue per segment) | `src/AcDream.App/UI/UiChatView.cs:13` | Retail glyph-run parsing lives inside keystone.dll with no PDB/decomp; per-line per-kind coloring is the correct tonal palette and covers all existing chat types | Chat lines retail renders with multiple colors or bold names (e.g. "PlayerName says: text") render as one flat color; subtle visual difference but functionally complete | `UIElement_Text` glyph-run styling (keystone.dll, no decomp) |
 | AP-40 | Single default translucency for the chat window chrome; no focused/unfocused opacity transition; dat font face/size taken from the vitals `vitalsDatFont` (same dat font, not a chat-specific size lookup) | `src/AcDream.App/Rendering/GameWindow.cs` (chatController binding line) | Retail fades the chat window to ~80% alpha when unfocused (`gmMainChatUI::UpdateAlpha @0x4cdea0`); the opacity animation deferred to the Plan-2 window-manager input integration; sharing `vitalsDatFont` is safe — retail uses the same AC-default font for both | The chat window is always fully opaque/same-font rather than subtly fading when idle; no wrong text, but the focused/unfocused breathing rhythm is absent | `gmMainChatUI::UpdateAlpha` @0x4cdea0; `UCF::SetAceFont @0x4d3940` |
-| AP-41 | Scrollbar thumb drawn as a single stretched sprite (`0x06004C63`, the 3-slice middle tile) instead of retail's 3-slice: top cap `0x06004C60` + tiled middle `0x06004C63` + bottom cap `0x06004C66` | `src/AcDream.App/UI/UiChatScrollbar.cs:37` | The middle tile stretches acceptably at chat-panel dimensions; the 3-slice port is a Task-H upgrade acknowledged inline in the `ThumbSprite` property comment | The thumb's top and bottom edges lack the retail end-cap sprites — slightly wrong visual shape at small thumb sizes (thumb too-short for the middle tile to cleanly scale) | `UIElement_Scrollbar::UpdateLayout @0x4710d0`; cap sprites `0x06004C60` (top) + `0x06004C66` (bottom) from base layout `0x2100003E` |
+| AP-41 | Scrollbar thumb 3-slice cap fallback only: single-tile draw (`0x06004C63`) used only when `ThumbTopSprite`/`ThumbBotSprite` are unset; the chat controller passes all three cap ids so the 3-slice path is drawn in practice | `src/AcDream.App/UI/UiScrollbar.cs:35` | The fallback single-tile path is unreachable when caps are bound (chat controller always sets them); the 3-slice path is the active code path | Only if a future caller omits the cap ids will the fallback fire — no visual regression in the chat window | `UIElement_Scrollbar::UpdateLayout @0x4710d0`; cap sprites `0x06004C60` (top) + `0x06004C66` (bottom) from base layout `0x2100003E` |
 
 ---
 

src/AcDream.App/UI/Layout/ChatWindowController.cs

@@ -20,9 +20,9 @@ namespace AcDream.App.UI.Layout;
 /// <see cref="ElementInfo"/> tree (which contains everything) and adds the behavioral
 /// widgets as children of their parent container widgets (transcript panel
 /// <c>0x10000010</c> / input bar <c>0x10000013</c>) which ARE created as
-/// <see cref="UiDatElement"/> nodes. The scrollbar track (<c>0x10000012</c>) and
+/// <see cref="UiDatElement"/> nodes. The scrollbar track (<c>0x10000012</c>) is built
-/// channel menu (<c>0x10000014</c>) are created by the factory and are replaced
+/// directly as a <see cref="UiScrollbar"/> by the factory (Type 11) and is bound in place
-/// with their behavioral counterparts here.
+/// here. The channel menu (<c>0x10000014</c>) is still replaced with its behavioral counterpart.
 /// </para>
 /// </summary>
 public sealed class ChatWindowController
@@ -71,7 +71,7 @@ public sealed class ChatWindowController
     public UiChatInput Input { get; private set; } = null!;
 
     /// <summary>Scrollbar widget, driven by <see cref="Transcript"/>'s scroll model.</summary>
-    public UiChatScrollbar Scrollbar { get; private set; } = null!;
+    public UiScrollbar Scrollbar { get; private set; } = null!;
 
     /// <summary>Channel-selector menu widget.</summary>
     public UiChannelMenu Menu { get; private set; } = null!;
@@ -110,7 +110,7 @@ public sealed class ChatWindowController
     /// <param name="debugFont">Fallback debug bitmap font (used when
     ///   <paramref name="datFont"/> is null).</param>
     /// <param name="resolve">Dat RenderSurface id → (GL tex handle, px width, px height).
-    ///   Forwarded to <see cref="UiChatScrollbar"/> and <see cref="UiChannelMenu"/>.</param>
+    ///   Forwarded to <see cref="UiScrollbar"/> and <see cref="UiChannelMenu"/>.</param>
     public static ChatWindowController? Bind(
         ElementInfo rootInfo,
         ImportedLayout layout,
@@ -196,33 +196,24 @@ public sealed class ChatWindowController
         inputBar.AddChild(c.Input);
         c.Input.OnSubmit = text => ChatCommandRouter.Submit(text, vm, busProvider(), c._activeChannel);
 
-        // ── Scrollbar — replace the imported track placeholder ────────────
+        // ── Scrollbar — bind the factory-built Type-11 track element ────────
-        // The factory created a UiDatElement for the track. Remove it and place a
+        // The factory now builds the Type-11 track element (0x10000012) as a UiScrollbar
-        // behavioral UiChatScrollbar at the same position, driving the transcript's scroll.
+        // directly. Find it, bind it in place — no remove/add needed.
         var track = layout.FindElement(TrackId);
-        if (track?.Parent is { } trackParent)
+        if (track is UiScrollbar bar)
         {
-            c.Scrollbar = new UiChatScrollbar
+            float oldTop = bar.Top;
-            {
+            bar.Top    = 0f;                       // pull up to the panel top (resize-bar reclaim)
-                // Pull the bar up to the panel top so the top arrow meets the window
+            bar.Height = bar.Height + oldTop;
-                // border (and lines up with the max/min button at root y=0); the dat
+            bar.Model         = c.Transcript.Scroll;
-                // track sits 6px down, which left a gap after the resize-bar reclaim.
+            bar.SpriteResolve = resolve;
-                Left         = track.Left,
+            bar.TrackSprite    = TrackSprite;
-                Top          = 0f,
+            bar.ThumbSprite    = ThumbSprite;
-                Width        = track.Width,
+            bar.ThumbTopSprite = ThumbTopSprite;
-                Height       = track.Height + track.Top,
+            bar.ThumbBotSprite = ThumbBotSprite;
-                Anchors      = track.Anchors,
+            bar.UpSprite       = UpSprite;
-                Model        = c.Transcript.Scroll,
+            bar.DownSprite     = DownSprite;
-                SpriteResolve = resolve,
+            c.Scrollbar = bar;
-                TrackSprite    = TrackSprite,
-                ThumbSprite    = ThumbSprite,
-                ThumbTopSprite = ThumbTopSprite,
-                ThumbBotSprite = ThumbBotSprite,
-                UpSprite       = UpSprite,
-                DownSprite     = DownSprite,
-            };
-            trackParent.RemoveChild(track);
-            trackParent.AddChild(c.Scrollbar);
         }
 
         // ── Channel menu — replace the imported menu placeholder ──────────

src/AcDream.App/UI/Layout/DatWidgetFactory.cs

@@ -58,6 +58,7 @@ public static class DatWidgetFactory
         UiElement e = info.Type switch
         {
             7  => BuildMeter(info, resolve, datFont),  // UIElement_Meter
+            11 => new UiScrollbar(),                   // UIElement_Scrollbar (reg :124137)
             _  => new UiDatElement(info, resolve),     // generic fallback for all other types
         };
 

src/AcDream.App/UI/UiChatView.cs

@@ -52,7 +52,7 @@ public sealed class UiChatView : UiElement
     /// <summary>Inner text inset from the view edges, px.</summary>
     public float Padding { get; set; } = 4f;
 
-    /// <summary>The scroll model — also read by the linked UiChatScrollbar.</summary>
+    /// <summary>The scroll model — also read by the linked UiScrollbar.</summary>
     public UiScrollable Scroll { get; } = new();
 
     /// <summary>True while the view is pinned to the newest line (auto-scrolls as content grows).</summary>

src/AcDream.App/UI/UiScrollable.cs

@@ -7,7 +7,7 @@ namespace AcDream.App.UI;
 /// the scroll offset is an integer pixel value (<c>m_iScrollableY</c>) clamped to
 /// [0, ContentHeight - ViewHeight]; the thumb ratio is view/content; the position
 /// ratio is scroll/(content-view). Pure (no GL) so it is fully unit-tested and
-/// shared by the transcript (UiChatView) and the scrollbar (UiChatScrollbar).
+/// shared by the transcript (UiChatView) and the scrollbar (UiScrollbar).
 /// Decomp anchors: SetScrollableXY @0x4740c0, UpdateScrollbarSize_ @0x4741a0,
 /// UpdateScrollbarPosition_ @0x473f20, UIElement_Text::InqScrollDelta @0x4689b0.
 /// </summary>

src/AcDream.App/UI/UiScrollbar.cs

@@ -4,11 +4,9 @@ using System.Numerics;
 namespace AcDream.App.UI;
 
 /// <summary>
-/// Right-side chat scrollbar: a track sprite, a draggable thumb sized to the
+/// Generic scrollbar. Ports retail <c>UIElement_Scrollbar</c>
-/// content/view ratio, and up/down step buttons. Drives a linked
+/// (RegisterElementClass(0xb) @ acclient_2013_pseudo_c.txt:124137);
-/// <see cref="UiScrollable"/>. Ports retail <c>UIElement_Scrollbar::UpdateLayout
+/// thumb size = trackLen * ThumbRatio (min 8px); step ±1 line.
-/// @0x4710d0</c> (thumb size = trackLen * ThumbRatio, min 8px; thumb pos from
-/// PositionRatio) and <c>HandleButtonClick @0x470e90</c> (step ±1 line).
 /// </summary>
 /// <remarks>
 /// Dat element ids (chat LayoutDesc 0x21000006): track 0x10000012 (X=474 Y=6 W=16 H=68),
@@ -22,7 +20,7 @@ namespace AcDream.App.UI;
 /// rendered scrollbar's height; the widget responds to those regions directly via hit
 /// comparison in OnEvent without requiring separate child elements.
 /// </remarks>
-public sealed class UiChatScrollbar : UiElement
+public sealed class UiScrollbar : UiElement
 {
     /// <summary>The scroll model this bar reflects + drives (shared with the transcript).</summary>
     public UiScrollable? Model { get; set; }
@@ -61,7 +59,7 @@ public sealed class UiChatScrollbar : UiElement
     private bool _draggingThumb;
     private float _dragOffsetY;
 
-    public UiChatScrollbar() { CapturesPointerDrag = true; }
+    public UiScrollbar() { CapturesPointerDrag = true; }
 
     /// <summary>
     /// Computes the thumb rectangle (local y origin and height) within the track area

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

@@ -97,6 +97,15 @@ public class DatWidgetFactoryTests
         Assert.Null(DatWidgetFactory.Create(noMedia, NoTex, null));
     }
 
+    // ── Test 5b: Type 11 → UiScrollbar ──────────────────────────────────────
+
+    [Fact]
+    public void Type11_Scrollbar_MakesUiScrollbar()
+    {
+        var e = DatWidgetFactory.Create(new ElementInfo { Type = 11, Width = 16, Height = 68 }, NoTex, null);
+        Assert.IsType<UiScrollbar>(e);
+    }
+
     // ── Test 6: Meter slice extraction (the important one) ───────────────────
 
     /// <summary>

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

@@ -4,9 +4,9 @@ using Xunit;
 namespace AcDream.App.Tests.UI;
 
 /// <summary>
-/// Pure unit tests for <see cref="UiChatScrollbar.ThumbRect"/> — no GL dependency.
+/// Pure unit tests for <see cref="UiScrollbar.ThumbRect"/> — no GL dependency.
 /// </summary>
-public class UiChatScrollbarTests
+public class UiScrollbarTests
 {
     // Model: content=400, view=100, trackLen=200.
     // ThumbRatio = 100/400 = 0.25  →  thumbH = max(8, 200*0.25) = 50.
@@ -17,7 +17,7 @@ public class UiChatScrollbarTests
     {
         var m = new UiScrollable { ContentHeight = 400, ViewHeight = 100 };
         // PositionRatio = 0 (start).
-        var (y, h) = UiChatScrollbar.ThumbRect(m, trackTop: 0f, trackLen: 200f);
+        var (y, h) = UiScrollbar.ThumbRect(m, trackTop: 0f, trackLen: 200f);
         Assert.Equal(50f, h, 3f);
         Assert.Equal(0f, y, 3f);
     }
@@ -28,7 +28,7 @@ public class UiChatScrollbarTests
         var m = new UiScrollable { ContentHeight = 400, ViewHeight = 100 };
         m.ScrollToEnd(); // PositionRatio = 1.
         float trackTop = 16f, trackLen = 200f;
-        var (y, h) = UiChatScrollbar.ThumbRect(m, trackTop, trackLen);
+        var (y, h) = UiScrollbar.ThumbRect(m, trackTop, trackLen);
         Assert.Equal(50f, h, 3f);
         // y = trackTop + travel * 1 = 16 + 150 = 166.
         Assert.Equal(166f, y, 3f);
@@ -41,7 +41,7 @@ public class UiChatScrollbarTests
         // thumbH=50; travel=150; y = trackTop + 150 = trackTop + 150.
         var m = new UiScrollable { ContentHeight = 400, ViewHeight = 100 };
         m.ScrollToEnd();
-        var (y, h) = UiChatScrollbar.ThumbRect(m, trackTop: 16f, trackLen: 200f);
+        var (y, h) = UiScrollbar.ThumbRect(m, trackTop: 16f, trackLen: 200f);
         Assert.Equal(50f, h, 3f);
         Assert.Equal(166f, y, 3f); // 16 + 150
     }
@@ -54,7 +54,7 @@ public class UiChatScrollbarTests
         m.SetScrollY(150);
         Assert.Equal(0.5f, m.PositionRatio, 3);
 
-        var (y, h) = UiChatScrollbar.ThumbRect(m, trackTop: 0f, trackLen: 200f);
+        var (y, h) = UiScrollbar.ThumbRect(m, trackTop: 0f, trackLen: 200f);
         Assert.Equal(50f, h, 3f);
         // y = 0 + 150 * 0.5 = 75.
         Assert.Equal(75f, y, 3f);
@@ -65,7 +65,7 @@ public class UiChatScrollbarTests
     {
         // content=1000, view=10, trackLen=200 → ThumbRatio=0.01 → raw=2 < 8 → clamp to 8.
         var m = new UiScrollable { ContentHeight = 1000, ViewHeight = 10 };
-        var (_, h) = UiChatScrollbar.ThumbRect(m, trackTop: 0f, trackLen: 200f);
+        var (_, h) = UiScrollbar.ThumbRect(m, trackTop: 0f, trackLen: 200f);
         Assert.Equal(8f, h, 3f);
     }
 
@@ -74,7 +74,7 @@ public class UiChatScrollbarTests
     {
         // content <= view → ThumbRatio = 1 → thumbH = trackLen.
         var m = new UiScrollable { ContentHeight = 50, ViewHeight = 100 };
-        var (y, h) = UiChatScrollbar.ThumbRect(m, trackTop: 16f, trackLen: 100f);
+        var (y, h) = UiScrollbar.ThumbRect(m, trackTop: 16f, trackLen: 100f);
         Assert.Equal(100f, h, 3f);
         Assert.Equal(16f, y, 3f); // travel = 0 → y = trackTop
     }