diff --git a/src/AcDream.App/UI/UiChatView.cs b/src/AcDream.App/UI/UiChatView.cs
index 1392c26f..9dbe9cd3 100644
--- a/src/AcDream.App/UI/UiChatView.cs
+++ b/src/AcDream.App/UI/UiChatView.cs
@@ -52,8 +52,12 @@ public sealed class UiChatView : UiElement
     /// <summary>Inner text inset from the view edges, px.</summary>
     public float Padding { get; set; } = 4f;
 
-    // Pixels the transcript is scrolled UP from the newest line (0 = pinned to bottom).
-    private float _scroll;
+    /// <summary>The scroll model — also read by the linked UiChatScrollbar.</summary>
+    public UiScrollable Scroll { get; } = new();
+
+    /// <summary>True while the view is pinned to the newest line (auto-scrolls as content grows).</summary>
+    private bool _pinBottom = true;
+
     private const float WheelLines = 1f;   // lines advanced per wheel notch (retail = 1 line per notch)
 
     // ── Cached layout from the last OnDraw, so OnEvent hit-tests the SAME geometry ──
@@ -112,11 +116,19 @@ public sealed class UiChatView : UiElement
         float top = Padding, bottom = Height - Padding;
         float innerH = bottom - top;
         float contentH = lines.Count * lh;
-        _scroll = ClampScroll(_scroll, contentH, innerH);
 
-        // Bottom-pin: with _scroll==0 the LAST line ends at `bottom`; scrolling up
-        // shifts the whole block down so older lines are revealed at the top.
-        float baseY = bottom - contentH + _scroll;
+        // Drive the shared scroll model with the current geometry.
+        Scroll.LineHeight = (int)MathF.Round(lh);
+        Scroll.ContentHeight = (int)MathF.Ceiling(contentH);
+        Scroll.ViewHeight = (int)MathF.Floor(innerH);
+        if (_pinBottom) Scroll.ScrollToEnd();
+
+        // 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);
         _lastBaseY = baseY;
 
         // Normalised selection span (start <= end), if any.
@@ -166,9 +178,11 @@ public sealed class UiChatView : UiElement
         {
             case UiEventType.Scroll:
             {
-                float lh = DatFont?.LineHeight ?? (Font ?? _lastFont)?.LineHeight ?? 16f;
-                // Silk wheel +Y = scroll up = reveal older = shift content down = larger _scroll.
-                _scroll += e.Data0 * WheelLines * lh;   // re-clamped next OnDraw against live content
+                // Silk wheel +Y = scroll up = reveal older = toward the TOP = decrease ScrollY.
+                // ScrollByLines sign: +down/newer, -up/older.
+                // e.Data0 > 0 → wheel up → want older → ScrollByLines with negative lines.
+                Scroll.ScrollByLines((int)(-e.Data0 * WheelLines));
+                _pinBottom = Scroll.AtEnd;
                 return true;
             }