fix(ui): complete retail inventory scroll polish

Preserve pixel scroll offsets across inventory rebuilds, crop partially visible rows with nested geometry/UV clips, and replace the obsolete 560px resize ceiling with available screen height. Keep retail's row-sized wheel step while allowing continuous scrollbar thumb positions.

Co-Authored-By: Codex <codex@openai.com>

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

@@ -291,6 +291,21 @@ public class InventoryControllerTests
         Assert.Same(grid.Scroll, bar.Model);            // the bar drives the grid's scroll
     }
 
+    [Fact]
+    public void Inventory_refresh_preserves_contents_pixel_scroll_offset()
+    {
+        var (layout, grid, _, _, _, _, _, _) = BuildLayout();
+        var objects = new ClientObjectTable();
+        objects.AddOrUpdate(new ClientObject { ObjectId = Player, ItemsCapacity = 102 });
+        Bind(layout, objects);
+        grid.Scroll.SetScrollY(40);
+
+        objects.UpdateIntProperty(Player, 5u, 1000);
+
+        Assert.Equal(40, grid.Scroll.ScrollY);
+        Assert.Equal(-8f, grid.GetItem(6)!.Top);
+    }
+
     [Fact]
     public void Contents_grid_pads_empty_slots_to_main_pack_capacity()
     {

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

@@ -147,7 +147,8 @@ public sealed class RetailWindowFrameTests
         grid.LayoutCells();
 
         Assert.Equal(251f, grid.Height);
-        Assert.Equal(42, grid.Children.Count(child => child.Visible));
+        Assert.Equal(48, grid.Children.Count(child => child.Visible));
+        Assert.Equal(224f, grid.GetItem(42)!.Top); // final row intersects 251px view by 27px
     }
 
     private static void ApplyAnchors(UiElement parent)

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

@@ -0,0 +1,36 @@
+using AcDream.App.UI;
+using Xunit;
+
+namespace AcDream.App.Tests.UI;
+
+public sealed class UiClipRectTests
+{
+    [Fact]
+    public void TryClipSprite_cropsGeometryAndMatchingUvs()
+    {
+        var clip = new UiClipRect(0f, 0f, 100f, 100f);
+        float x = -8f, y = 88f, w = 32f, h = 32f;
+        float u0 = 0f, v0 = 0f, u1 = 1f, v1 = 1f;
+
+        bool visible = UiClipRect.TryClipSprite(
+            clip, ref x, ref y, ref w, ref h, ref u0, ref v0, ref u1, ref v1);
+
+        Assert.True(visible);
+        Assert.Equal((0f, 88f, 24f, 12f), (x, y, w, h));
+        Assert.Equal((0.25f, 0f, 1f, 0.375f), (u0, v0, u1, v1));
+    }
+
+    [Fact]
+    public void Intersection_andFullyOutsideSprite_areEmpty()
+    {
+        UiClipRect intersection = UiClipRect.Intersect(
+            new UiClipRect(0f, 0f, 20f, 20f),
+            new UiClipRect(30f, 30f, 40f, 40f));
+        float x = 0f, y = 0f, w = 10f, h = 10f;
+        float u0 = 0f, v0 = 0f, u1 = 1f, v1 = 1f;
+
+        Assert.True(intersection.IsEmpty);
+        Assert.False(UiClipRect.TryClipSprite(
+            intersection, ref x, ref y, ref w, ref h, ref u0, ref v0, ref u1, ref v1));
+    }
+}

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

@@ -52,6 +52,40 @@ public sealed class UiItemListScrollTests
         Assert.True(list.GetItem(18)!.Visible);         // row 3 now visible
     }
 
+    [Fact]
+    public void Pixel_scroll_keeps_partiallyVisible_edge_rows()
+    {
+        var list = Grid(30);
+
+        list.Scroll.SetScrollY(8);
+        list.LayoutCells();
+
+        Assert.True(list.GetItem(0)!.Visible);
+        Assert.Equal(-8f, list.GetItem(0)!.Top);
+        Assert.True(list.GetItem(18)!.Visible);
+        Assert.Equal(88f, list.GetItem(18)!.Top);
+        Assert.False(list.GetItem(24)!.Visible);
+        Assert.Null(list.HitTest(5f, -1f));
+        Assert.IsType<UiItemSlot>(list.HitTest(5f, 1f));
+    }
+
+    [Fact]
+    public void Deferred_rebuild_preserves_pixel_scroll_offset()
+    {
+        var list = Grid(30);
+        list.Scroll.SetScrollY(40);
+
+        using (list.DeferLayout())
+        {
+            list.Flush();
+            for (int i = 0; i < 30; i++)
+                list.AddItem(new UiItemSlot());
+        }
+
+        Assert.Equal(40, list.Scroll.ScrollY);
+        Assert.Equal(-8f, list.GetItem(6)!.Top);
+    }
+
     [Fact]
     public void Scroll_survives_the_per_frame_anchor_pass()
     {