feat(ui): Slice 5.4 — the authored vendor browse panel (LayoutDesc 0x21000012)

The vendor window is retail's own: LayoutDesc 0x21000012, root
0x100000B7, found by enumerating all 101 layouts for the one
containing both known tab controls and clinched by the root's Type
0x10000017 — the literal UIElement::RegisterElementClass id for
gmVendorUI (pc:202075). Discovery evidence and the D0 read live in
the research doc's new §B.4.

D0 corrected two assumptions: retail's category "tabs" are a UiMenu
DROPDOWN fed by a hardcoded 18-row ordered category table (ported
bit-for-bit against our ItemType enum; list always scoped to exactly
one category, first-present wins, selection preserved across refresh
per retail's clamp), and the layout authors THREE tabs — Items
(browse, this slice), Buying and Selling (staged-transaction review,
Slice 6) — decision 4's "browse/Buy tab" names the Items tab retail's
mode-2 OpenTab opens. The non-default tabs render and switch pages
but stay inert, fenced in comments.

VendorUiController mounts Items: category dropdown, icon-cell item
row with the retained scrollbar, per-unit retail pricing via
VendorPricing.SellPrice (the vendor-stock path VendorProfile::
VendorSellPrice feeds), name/cost on selection. The panel is a pure
projection of VendorState — opens on populate, closes on clear; the
close button's VendorState.Close() is its only permitted mutation.
Nothing on the wire.

AP-110 narrowed (vendor leaves the absent-panels list); AP-161 files
the precise Slice-6 remainder (Buying/Selling unwired, Buy/Add
buttons, InqAcceptability). Twelve controller tests on a real-dat
fixture. Clean-room complete solution: 11,323 passed / 4 skipped /
0 failed.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

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

@@ -183,6 +183,12 @@ public static class FixtureLoader
     public static ElementInfo LoadMiniGameInfos()
         => LoadInfos("mini_game_2100001E.json");
 
+    public static ImportedLayout LoadVendor()
+        => LayoutImporter.Build(LoadVendorInfos(), _ => (0u, 0, 0), null);
+
+    public static ElementInfo LoadVendorInfos()
+        => LoadInfos("vendor_21000012_100000B7.json");
+
     // ── Shared loader ────────────────────────────────────────────────────────
 
     private static AcDream.App.UI.Layout.ElementInfo LoadInfos(string fileName)

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

@@ -136,6 +136,8 @@ public sealed class RetailLayoutFixtureGenerator
                 "examine_row_2100006B_10000166.json"),
             (AppraisalUiController.LayoutId, SpellExamineComponentTemplateFactory.TemplateId,
                 "examine_component_2100006B_1000032E.json"),
+            (VendorUiController.LayoutId, VendorUiController.RootId,
+                "vendor_21000012_100000B7.json"),
         })
         {
             ElementInfo? panelPart = LayoutImporter.ImportInfos(dats, layoutId, rootId);

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

@@ -0,0 +1,327 @@
+using System.Collections.Generic;
+using System.Linq;
+using AcDream.App.UI;
+using AcDream.App.UI.Layout;
+using AcDream.Core.Items;
+
+namespace AcDream.App.Tests.UI.Layout;
+
+/// <summary>
+/// Slice 5.4 — mirrors <see cref="ExternalContainerControllerTests"/>'s
+/// harness shape (hand-built <see cref="ImportedLayout"/> over
+/// <see cref="RetailWindowFrame.Mount"/>) for the behavioral suite, plus one
+/// real-dat-fixture smoke test (mirroring
+/// <c>AppraisalUiControllerTests</c>'s use of <see cref="FixtureLoader"/>)
+/// that catches drift between the hardcoded ids in
+/// <see cref="VendorUiController"/> and the actual LayoutDesc 0x21000012.
+/// </summary>
+public sealed class VendorUiControllerTests
+{
+    private const uint VendorGuid = 0x70000010u;
+    private const uint ArmorItemGuid = 0x60000101u;
+    private const uint FoodItemGuid = 0x60000102u;
+    private const uint StackedItemGuid = 0x60000103u;
+
+    private sealed class TestElement : UiElement { }
+
+    [Fact]
+    public void Bind_FromRealDatFixture_ResolvesAllRequiredControls()
+    {
+        ImportedLayout layout = FixtureLoader.LoadVendor();
+        var screen = new UiRoot { Width = 1280f, Height = 800f };
+        RetailWindowHandle window = RetailWindowFrame.Mount(
+            screen,
+            layout.Root,
+            static _ => (0u, 0, 0),
+            new RetailWindowFrame.Options
+            {
+                WindowName = "vendor-fixture-smoke",
+                Chrome = RetailWindowChrome.Imported,
+                Visible = false,
+            });
+
+        VendorUiController? controller = VendorUiController.Bind(
+            layout,
+            new VendorState(),
+            window,
+            static (_, _, _, _, _) => 0u);
+
+        Assert.NotNull(controller);
+    }
+
+    private sealed class Harness
+    {
+        public readonly VendorState State = new();
+        public readonly UiRoot Screen = new() { Width = 800f, Height = 600f };
+        public readonly UiItemList ItemList = new();
+        public readonly UiScrollbar ItemScrollbar = new();
+        public readonly UiMenu TypeMenu = new();
+        public readonly UiText ItemNameText = new();
+        public readonly UiText ItemCostText = new();
+        public readonly UiText ItemsTab = new();
+        public readonly UiText BuyingTab = new();
+        public readonly UiText SellingTab = new();
+        public readonly UiElement ItemsPage = new TestElement();
+        public readonly UiElement BuyingPage = new TestElement();
+        public readonly UiElement SellingPage = new TestElement();
+        public readonly UiButton CloseButton;
+        public readonly RetailWindowHandle Window;
+        public readonly VendorUiController Controller;
+
+        public Harness()
+        {
+            var root = new TestElement { Width = 800f, Height = 110f };
+            CloseButton = new UiButton(
+                new ElementInfo { Id = VendorUiController.CloseId, Type = 1 },
+                static _ => (0u, 0, 0));
+
+            root.AddChild(CloseButton);
+            root.AddChild(ItemsTab);
+            root.AddChild(BuyingTab);
+            root.AddChild(SellingTab);
+            root.AddChild(ItemsPage);
+            root.AddChild(BuyingPage);
+            root.AddChild(SellingPage);
+            ItemsPage.AddChild(ItemList);
+            ItemsPage.AddChild(ItemScrollbar);
+            ItemsPage.AddChild(TypeMenu);
+            ItemsPage.AddChild(ItemNameText);
+            ItemsPage.AddChild(ItemCostText);
+
+            var layout = new ImportedLayout(root, new Dictionary<uint, UiElement>
+            {
+                [VendorUiController.CloseId] = CloseButton,
+                [VendorUiController.ItemsTabId] = ItemsTab,
+                [VendorUiController.BuyingTabId] = BuyingTab,
+                [VendorUiController.SellingTabId] = SellingTab,
+                [VendorUiController.ItemsPageId] = ItemsPage,
+                [VendorUiController.BuyingPageId] = BuyingPage,
+                [VendorUiController.SellingPageId] = SellingPage,
+                [VendorUiController.ItemListId] = ItemList,
+                [VendorUiController.ItemScrollbarId] = ItemScrollbar,
+                [VendorUiController.TypeFilterMenuId] = TypeMenu,
+                [VendorUiController.ItemNameTextId] = ItemNameText,
+                [VendorUiController.ItemCostTextId] = ItemCostText,
+            });
+
+            Window = RetailWindowFrame.Mount(
+                Screen,
+                root,
+                static _ => (0u, 0, 0),
+                new RetailWindowFrame.Options
+                {
+                    WindowName = WindowNames.Vendor,
+                    Chrome = RetailWindowChrome.Imported,
+                    Visible = false,
+                    Draggable = false,
+                    Resizable = false,
+                });
+
+            Controller = VendorUiController.Bind(
+                layout,
+                State,
+                Window,
+                static (_, iconId, _, _, _) => iconId != 0u ? iconId + 1000u : 0u)!;
+            Screen.WindowManager.AttachController(WindowNames.Vendor, Controller);
+        }
+    }
+
+    private static VendorShopProfile Profile(
+        float sellRate = 1.5f, uint altCurrency = 0u, string altName = "") =>
+        new(0u, 0u, 0u, false, 1.0f, sellRate, altCurrency, 0u, altName);
+
+    private static string GetText(UiText text)
+        => string.Concat(text.LinesProvider().Select(line => line.Text));
+
+    [Fact]
+    public void Bind_WiresTheScrollbarToTheItemListsScrollModel()
+    {
+        var h = new Harness();
+
+        Assert.True(h.ItemScrollbar.Horizontal);
+        Assert.Same(h.ItemList.Scroll, h.ItemScrollbar.Model);
+    }
+
+    [Fact]
+    public void Opened_ShowsWindowAndPopulatesFirstPresentCategoryInTableOrder()
+    {
+        var h = new Harness();
+        var items = new[]
+        {
+            // Food is table entry #5, Armor is #1 — retail's fixed table
+            // order, not insertion order, decides the default selection.
+            new VendorShopItem(FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 5),
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+        };
+
+        h.State.Apply(VendorGuid, Profile(), items);
+
+        Assert.True(h.Window.IsVisible);
+        Assert.True(h.ItemsPage.Visible);
+        Assert.False(h.BuyingPage.Visible);
+        Assert.False(h.SellingPage.Visible);
+        Assert.Equal(1, h.ItemList.GetNumUIItems());
+        Assert.Equal(ArmorItemGuid, h.ItemList.GetItem(0)!.ItemId);
+        Assert.Equal("Armor", h.TypeMenu.Items.Single(i => Equals(i.Payload, h.TypeMenu.Selected)).Label);
+    }
+
+    [Fact]
+    public void Closed_HidesWindowAndClearsListAndText()
+    {
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(), new[]
+        {
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+        });
+        h.ItemList.GetItem(0)!.Clicked?.Invoke();
+        Assert.True(h.Window.IsVisible);
+        Assert.NotEqual(string.Empty, GetText(h.ItemNameText));
+
+        h.State.Close();
+
+        Assert.False(h.Window.IsVisible);
+        Assert.Equal(0, h.ItemList.GetNumUIItems());
+        Assert.Equal(string.Empty, GetText(h.ItemNameText));
+        Assert.Equal(string.Empty, GetText(h.ItemCostText));
+        Assert.Empty(h.TypeMenu.Items);
+    }
+
+    [Fact]
+    public void Reset_HidesWindowAndClearsContent()
+    {
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(), new[]
+        {
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+        });
+
+        h.State.Reset();
+
+        Assert.False(h.Window.IsVisible);
+        Assert.Equal(0, h.ItemList.GetNumUIItems());
+    }
+
+    [Fact]
+    public void SelectingItem_ShowsRetailCorrectPerUnitPrice_ForStackedItem()
+    {
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(sellRate: 2.0f), new[]
+        {
+            // Value=1000 is the STACK-TOTAL wire value for a 100-unit stack;
+            // per-unit = 1000/100 = 10. SellPrice = ceil(2.0*10*1 - 0.1) = 20
+            // (VendorPricing.SellPrice, ShopSystem::SellPrice pc:702107).
+            new VendorShopItem(
+                StackedItemGuid, -1, 3u, "Arrows", (uint)ItemType.MissileWeapon, 300u, 1000,
+                DescStackSize: 100),
+        });
+
+        h.ItemList.GetItem(0)!.Clicked?.Invoke();
+
+        Assert.Equal("Arrows", GetText(h.ItemNameText));
+        Assert.Equal("20", GetText(h.ItemCostText));
+    }
+
+    [Fact]
+    public void SelectingItem_WithAlternateCurrency_AppendsCurrencyName()
+    {
+        var h = new Harness();
+        h.State.Apply(
+            VendorGuid,
+            Profile(sellRate: 1.0f, altCurrency: 0x12345678u, altName: "Trade Notes"),
+            new[]
+            {
+                new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 50),
+            });
+
+        h.ItemList.GetItem(0)!.Clicked?.Invoke();
+
+        Assert.Equal("50 Trade Notes", GetText(h.ItemCostText));
+    }
+
+    [Fact]
+    public void SelectingDifferentCategory_FiltersItemListToThatCategoryOnly()
+    {
+        var h = new Harness();
+        var armor = new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500);
+        var food = new VendorShopItem(FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 5);
+        h.State.Apply(VendorGuid, Profile(), new[] { armor, food });
+        Assert.Equal(ArmorItemGuid, h.ItemList.GetItem(0)!.ItemId); // default: Armor (table order)
+
+        object? foodPayload = h.TypeMenu.Items.First(i => i.Label == "Food").Payload;
+        h.TypeMenu.OnSelect!.Invoke(foodPayload);
+
+        Assert.Equal(1, h.ItemList.GetNumUIItems());
+        Assert.Equal(FoodItemGuid, h.ItemList.GetItem(0)!.ItemId);
+    }
+
+    [Fact]
+    public void CloseButton_RoutesThroughVendorStateClose_NotADirectFieldWrite()
+    {
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(), new[]
+        {
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+        });
+
+        h.CloseButton.OnClick!.Invoke();
+
+        // The panel never mutates VendorState directly — the ONLY path from
+        // the close button to a cleared session is VendorState.Close()
+        // itself, so VendorId reads back 0 through the owner's own public
+        // surface, not a private field poke.
+        Assert.Equal(0u, h.State.VendorId);
+        Assert.False(h.Window.IsVisible);
+    }
+
+    [Fact]
+    public void SellingTab_SwitchesPageButPopulatesNoSellContent()
+    {
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(), new[]
+        {
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+        });
+
+        h.SellingTab.OnClick!.Invoke();
+
+        Assert.True(h.SellingPage.Visible);
+        Assert.False(h.ItemsPage.Visible);
+        Assert.False(h.BuyingPage.Visible);
+        // Slice 6 fence: no sell-list/price/button wiring exists at all —
+        // the page is exactly the authored-empty container it started as.
+        Assert.Empty(h.SellingPage.Children);
+    }
+
+    [Fact]
+    public void BuyingTab_SwitchesPageButPopulatesNoBuyContent()
+    {
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(), new[]
+        {
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+        });
+
+        h.BuyingTab.OnClick!.Invoke();
+
+        Assert.True(h.BuyingPage.Visible);
+        Assert.False(h.ItemsPage.Visible);
+        Assert.Empty(h.BuyingPage.Children);
+    }
+
+    [Fact]
+    public void ItemsTab_ReselectedAfterVisitingOtherTabs_ShowsBrowseListAgain()
+    {
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(), new[]
+        {
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+        });
+        h.SellingTab.OnClick!.Invoke();
+
+        h.ItemsTab.OnClick!.Invoke();
+
+        Assert.True(h.ItemsPage.Visible);
+        Assert.False(h.SellingPage.Visible);
+        Assert.Equal(1, h.ItemList.GetNumUIItems());
+    }
+}