feat(vendor): Slice 6 buy arc — shop items are real objects, vendor selection is THE selection, and Buy works (0x005F)

Three ordered pieces in one landing (the shared controller/composition
files carry all three; the internal order was 6.1 -> 6.2 -> 6.3):

6.1 VendorShopItemMaterializer diff-merges the shop list into the live
ClientObjectTable on VendorState transitions (so client-local close and
session teardown retire the entries too) and never claims a guid it did
not add — ACE's UniqueItemsForSale can re-list a guid a player once
held (AP-163 files the collision-skip; no retail counterpart traced).
Right-click examine on shop items now routes through the ordinary
appraisal path — the 5.4 F7c blocker dissolves with the table entries.

6.2 SelectionChangeSource.Vendor: row clicks, auto-select, and examine
all flow through the canonical SelectionState; the status bar and the
existing byte-faithful StackSplitQuantityState slider light up
unmodified. VendorSplitPolicy is the single 0xDC41CB0 mask owner; the
slider VALUE seeds to 1 for exempt items while maxSplitSize keeps the
stack (the splitSize/maxSplitSize distinction, research §B.3).
Selection clears at retail's actual site — VendorItemsUI::RemoveFromShop
(pc:202848), not a CloseVendor-level clear that does not exist.

6.3 BuildBuy (0x005F): vendorGuid, count, (i32 amount, u32 guid) pairs,
and the trailing alternateCurrencyId the REAL client sends
(CM_Vendor::Event_Buy pc:689288) though ACE's reader ignores it.
TryBuy rides the EXISTING J5.2 one-request-at-a-time reservation and
completes on UseDone; the Buy button disables while a request is in
flight. The reconciliation round-trip (money property update, inventory
CreateObject, ApproachVendor refresh -> panel rebuild) is proven by a
synthetic-inbound test against existing machinery — no new owner.

Register: AP-161 narrowed (selection + examine residuals close;
staging/Sell remain; double-click-to-buy confirmed ABSENT from retail
with negative evidence cited — we match retail). AP-162 files the
conscious no-client-side-affordability-precheck deferral.

Clean-room complete solution: 11,368 passed / 4 skipped / 0 failed.

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

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

@@ -27,6 +27,7 @@ public sealed class ItemInteractionControllerTests
         public readonly List<uint> Drops = new();
         public readonly List<(uint Item, uint Amount)> SplitDrops = new();
         public readonly List<(uint Target, uint Item, uint Amount)> Gives = new();
+        public readonly List<(uint VendorGuid, uint ItemGuid, int Amount, uint AlternateCurrencyId)> Buys = new();
         public readonly List<string> Toasts = new();
         public readonly List<string> SystemMessages = new();
         public readonly List<CombatMode> CombatModeRequests = new();
@@ -94,7 +95,9 @@ public sealed class ItemInteractionControllerTests
                 },
                 combatState: Combat,
                 sendChangeCombatMode: CombatModeRequests.Add,
-                requestUse: requestUse);
+                requestUse: requestUse,
+                sendBuy: (vendorGuid, itemGuid, amount, alternateCurrencyId) =>
+                    Buys.Add((vendorGuid, itemGuid, amount, alternateCurrencyId)));
         }
 
         public ItemInteractionController Controller { get; }
@@ -2145,4 +2148,123 @@ public sealed class ItemInteractionControllerTests
         Assert.Equal(0, h.Controller.BusyCount);
         Assert.Equal(InteractionModeKind.None, h.Controller.InteractionState.Current.Kind);
     }
+
+    // ── Slice 6.3: TryBuy ───────────────────────────────────────────────
+
+    [Fact]
+    public void TryBuy_Succeeds_SendsBuyAndTakesTheSharedUseReservation()
+    {
+        var h = new Harness();
+
+        bool result = h.Controller.TryBuy(
+            vendorGuid: 0x40001000u,
+            itemGuid: 0x50002000u,
+            amount: 1,
+            alternateCurrencyId: 0u);
+
+        Assert.True(result);
+        Assert.Equal(
+            new[] { (0x40001000u, 0x50002000u, 1, 0u) },
+            h.Buys);
+        // BeginUseRequestReservation increments BusyCount synchronously,
+        // before/independent of any wire response -- this is what makes the
+        // Buy button disable immediately (research doc §A.4: "no second
+        // gate", the SAME BusyCount>0 check every other request rides).
+        Assert.Equal(1, h.Controller.BusyCount);
+    }
+
+    [Fact]
+    public void TryBuy_StackedQuantity_ForwardsTheExactAmount()
+    {
+        var h = new Harness();
+
+        Assert.True(h.Controller.TryBuy(0x40001000u, 0x50002001u, 25, 0u));
+
+        Assert.Equal(25, h.Buys.Single().Amount);
+    }
+
+    [Fact]
+    public void TryBuy_AlternateCurrencyVendor_ForwardsTheCurrencyWcid()
+    {
+        var h = new Harness();
+
+        Assert.True(h.Controller.TryBuy(0x40001000u, 0x50002000u, 1, 0x12345678u));
+
+        Assert.Equal(0x12345678u, h.Buys.Single().AlternateCurrencyId);
+    }
+
+    [Fact]
+    public void TryBuy_WhileAnotherRequestIsBusy_IsRejectedAndSendsNothing()
+    {
+        var h = new Harness();
+        h.Controller.IncrementBusyCount(); // simulates any other in-flight request
+
+        bool result = h.Controller.TryBuy(0x40001000u, 0x50002000u, 1, 0u);
+
+        Assert.False(result);
+        Assert.Empty(h.Buys);
+        Assert.Equal(1, h.Controller.BusyCount); // unchanged -- no second reservation taken
+    }
+
+    [Fact]
+    public void TryBuy_ASecondBuyWhileTheFirstIsInFlight_IsRejected()
+    {
+        var h = new Harness();
+        Assert.True(h.Controller.TryBuy(0x40001000u, 0x50002000u, 1, 0u));
+
+        bool second = h.Controller.TryBuy(0x40001000u, 0x50002001u, 1, 0u);
+
+        Assert.False(second);
+        Assert.Single(h.Buys);
+        Assert.Equal(1, h.Controller.BusyCount);
+    }
+
+    [Theory]
+    [InlineData(0u, 0x50002000u, 1)]
+    [InlineData(0x40001000u, 0u, 1)]
+    [InlineData(0x40001000u, 0x50002000u, 0)]
+    [InlineData(0x40001000u, 0x50002000u, -1)]
+    public void TryBuy_InvalidArguments_IsRejectedWithoutTakingAReservation(
+        uint vendorGuid, uint itemGuid, int amount)
+    {
+        var h = new Harness();
+
+        bool result = h.Controller.TryBuy(vendorGuid, itemGuid, amount, 0u);
+
+        Assert.False(result);
+        Assert.Empty(h.Buys);
+        Assert.Equal(0, h.Controller.BusyCount);
+    }
+
+    [Fact]
+    public void TryBuy_CompleteUse_ReleasesTheReservationAndReenablesFurtherRequests()
+    {
+        // Research doc §A.4: UseDone (0x01C7) is the completion signal for
+        // Buy, resolved through the SAME RuntimeInteractionTransactionState.
+        // CompleteUse the existing UseDone handler already calls -- no new
+        // completion plumbing needed on the receive side.
+        var h = new Harness();
+        Assert.True(h.Controller.TryBuy(0x40001000u, 0x50002000u, 1, 0u));
+        Assert.Equal(1, h.Controller.BusyCount);
+
+        h.Controller.CompleteUse(0);
+
+        Assert.Equal(0, h.Controller.BusyCount);
+        // The gate is free again -- a second Buy can now proceed.
+        Assert.True(h.Controller.TryBuy(0x40001000u, 0x50002001u, 1, 0u));
+        Assert.Equal(2, h.Buys.Count);
+    }
+
+    [Fact]
+    public void TryBuy_FailedUseDone_AlsoReleasesTheReservation()
+    {
+        // A.2's failure paths all still end in exactly one SendUseDoneEvent
+        // -- success or failure, the reservation resolves the same way.
+        var h = new Harness();
+        Assert.True(h.Controller.TryBuy(0x40001000u, 0x50002000u, 1, 0u));
+
+        h.Controller.CompleteUse(0x0009u); // an arbitrary nonzero WeenieError
+
+        Assert.Equal(0, h.Controller.BusyCount);
+    }
 }

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

@@ -94,6 +94,9 @@ public class SelectedObjectControllerTests
         public readonly Dictionary<uint, bool>   HasHealthMap    = new();
         public readonly Dictionary<uint, float>  ManaMap         = new();
         public readonly Dictionary<uint, uint>   StackMap        = new();
+        // Slice 6.2: vendor-owned split-exempt predicate — see
+        // SelectedObjectController.Bind's isVendorSplitExempt parameter.
+        public readonly Dictionary<uint, bool>   VendorSplitExemptMap = new();
 
         public void FireSelection(uint? g)
         {
@@ -135,7 +138,8 @@ public class SelectedObjectControllerTests
                 unsubscribeObjectUpdated: h =>
                 {
                     if (ObjectUpdatedHandler == h) ObjectUpdatedHandler = null;
-                });
+                },
+                isVendorSplitExempt: g => VendorSplitExemptMap.TryGetValue(g, out var v) && v);
     }
 
     // ── B1: Bind initialisation ──────────────────────────────────────────────

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

@@ -4,6 +4,8 @@ using AcDream.App.UI;
 using AcDream.App.UI.Layout;
 using AcDream.Core.Items;
 using AcDream.Core.Properties;
+using AcDream.Core.Selection;
+using AcDream.Runtime.Gameplay;
 
 namespace AcDream.App.Tests.UI.Layout;
 
@@ -41,13 +43,26 @@ public sealed class VendorUiControllerTests
                 Visible = false,
             });
 
+        var objects = new ClientObjectTable();
+        using var itemInteraction = new ItemInteractionController(
+            objects,
+            new RuntimeInteractionTransactionState(new InventoryTransactionState(objects)),
+            new InteractionState(),
+            playerGuid: static () => 0u,
+            sendUse: null,
+            sendUseWithTarget: null,
+            sendWield: null,
+            sendDrop: null);
         VendorUiController? controller = VendorUiController.Bind(
             layout,
             new VendorState(),
             window,
             static (_, _, _, _, _) => 0u,
-            new ClientObjectTable(),
+            objects,
             static () => 0u,
+            itemInteraction,
+            new SelectionState(),
+            new StackSplitQuantityState(),
             datFont: null,
             debugFont: null,
             static _ => (0u, 0, 0));
@@ -60,9 +75,11 @@ public sealed class VendorUiControllerTests
         // F2/F3: a deterministic non-zero player coin total so the cost-text
         // "(you have ...)" tail is assertable.
         public const int DefaultPlayerCoinValue = 1500;
-        private const uint PlayerGuid = 0x50000001u;
+        public const uint PlayerGuid = 0x50000001u;
 
         public readonly VendorState State = new();
+        public readonly SelectionState Selection = new();
+        public readonly StackSplitQuantityState SplitQuantity = new();
         public readonly UiRoot Screen = new() { Width = 800f, Height = 600f };
         public readonly ClientObjectTable Objects = new();
         public readonly UiItemList ItemList = new();
@@ -81,6 +98,9 @@ public sealed class VendorUiControllerTests
         public readonly UiButton AddButton;
         public readonly RetailWindowHandle Window;
         public readonly VendorUiController Controller;
+        public readonly List<uint> Examines = new();
+        public readonly List<(uint VendorGuid, uint ItemGuid, int Amount, uint AlternateCurrencyId)> Buys = new();
+        public readonly ItemInteractionController ItemInteraction;
 
         public Harness()
         {
@@ -145,6 +165,19 @@ public sealed class VendorUiControllerTests
                     Resizable = false,
                 });
 
+            ItemInteraction = new ItemInteractionController(
+                Objects,
+                new RuntimeInteractionTransactionState(new InventoryTransactionState(Objects)),
+                new InteractionState(),
+                playerGuid: static () => PlayerGuid,
+                sendUse: null,
+                sendUseWithTarget: null,
+                sendWield: null,
+                sendDrop: null,
+                sendExamine: Examines.Add,
+                sendBuy: (vendorGuid, itemGuid, amount, alternateCurrencyId) =>
+                    Buys.Add((vendorGuid, itemGuid, amount, alternateCurrencyId)));
+
             Controller = VendorUiController.Bind(
                 layout,
                 State,
@@ -155,6 +188,9 @@ public sealed class VendorUiControllerTests
                 static (_, iconId, underlay, overlay, effects) => iconId + underlay + overlay + effects,
                 Objects,
                 static () => PlayerGuid,
+                ItemInteraction,
+                Selection,
+                SplitQuantity,
                 datFont: null,
                 debugFont: null,
                 static _ => (0u, 0, 0))!;
@@ -611,4 +647,204 @@ public sealed class VendorUiControllerTests
         Assert.False(h.SellingPage.Visible);
         Assert.Equal(1, h.ItemList.GetNumUIItems());
     }
+
+    [Fact]
+    public void RightClickShopRow_SelectsAndRoutesThroughItemInteractionExamine()
+    {
+        // Slice 6.1: mirrors ExternalContainerControllerTests'
+        // RightClickLoot_selectsAndExaminesWithoutPickingUp — the shop list
+        // wires ExamineItemRequested the same way the container lists do,
+        // now that shop items are materialized into ClientObjectTable
+        // (AP-161 finding #2's examine gap closes here).
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(), new[]
+        {
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+            new VendorShopItem(FoodItemGuid, -1, 1u, "Bread", (uint)ItemType.Food, 100u, 5),
+        });
+        // Food, not the auto-selected Armor default, so the assertion below
+        // proves the right click itself drove the selection.
+        UiItemSlot? foodCell = null;
+        object? foodPayload = h.TypeMenu.Items.First(i => i.Label == "Food").Payload;
+        h.TypeMenu.OnSelect!.Invoke(foodPayload);
+        foodCell = h.ItemList.GetItem(0);
+        Assert.Equal(FoodItemGuid, foodCell!.ItemId);
+
+        foodCell.OnEvent(new UiEvent(0u, foodCell, UiEventType.RightClick));
+
+        Assert.Equal(new[] { FoodItemGuid }, h.Examines);
+        Assert.Equal("Bread", GetText(h.ItemNameText));
+        Assert.True(foodCell.Selected);
+    }
+
+    // ── Slice 6.3: Buy button ────────────────────────────────────────────
+
+    [Fact]
+    public void BuyButton_Press_NonStackedItem_BuysQuantityOne()
+    {
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(), new[]
+        {
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+        });
+        // F4 auto-selected the sole item; its own stack size (default/absent)
+        // is <=1, so StackSplitQuantityState was never seeded above 1 either
+        // (this harness doesn't mount SelectedObjectController, so the split
+        // state starts at its class default Value=1/Maximum=1 — exactly what
+        // production would also show for a non-stacked item).
+
+        h.BuyButton.OnClick!.Invoke();
+
+        Assert.Equal(
+            new[] { (VendorGuid, ArmorItemGuid, 1, 0u) },
+            h.Buys);
+    }
+
+    [Fact]
+    public void BuyButton_Press_StackedItem_UsesTheLiveSplitSliderQuantity()
+    {
+        // Slice 6.3: BuySingleItem (pc:201674-201681) reads the CURRENT
+        // slider value, not the full stack. This harness doesn't mount
+        // SelectedObjectController (the toolbar owns that seeding in
+        // production), so the test seeds SplitQuantity directly to stand in
+        // for "the player selected this item, then dragged the slider to
+        // 25" before pressing Buy.
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(), new[]
+        {
+            new VendorShopItem(
+                StackedItemGuid, -1, 3u, "Arrows", (uint)ItemType.MissileWeapon, 300u, 1000,
+                DescStackSize: 100),
+        });
+        h.SplitQuantity.Reset(100u, initialValue: 25u);
+
+        h.BuyButton.OnClick!.Invoke();
+
+        Assert.Equal(25, h.Buys.Single().Amount);
+    }
+
+    [Fact]
+    public void BuyButton_Press_AlternateCurrencyVendor_ForwardsTheVendorsTradeWcid()
+    {
+        var h = new Harness();
+        h.State.Apply(
+            VendorGuid,
+            Profile(altCurrency: 0x12345678u, altName: "Trade Notes", altAmount: 500u),
+            new[]
+            {
+                new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+            });
+
+        h.BuyButton.OnClick!.Invoke();
+
+        Assert.Equal(0x12345678u, h.Buys.Single().AlternateCurrencyId);
+    }
+
+    [Fact]
+    public void BuyButton_DisablesTheInstantAPurchaseIsInFlight_AndReenablesOnCompletion()
+    {
+        var h = new Harness();
+        h.State.Apply(VendorGuid, Profile(), new[]
+        {
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+        });
+        Assert.True(h.BuyButton.Enabled);
+
+        h.BuyButton.OnClick!.Invoke();
+
+        // TryBuy's reservation increments BusyCount synchronously, before
+        // any wire response — the button must reflect that immediately,
+        // with no per-frame polling (ItemInteractionController.StateChanged
+        // drives RecomputeBuyButtonEnabled).
+        Assert.False(h.BuyButton.Enabled);
+
+        h.ItemInteraction.CompleteUse(0);
+
+        Assert.True(h.BuyButton.Enabled);
+    }
+
+    [Fact]
+    public void BuyButton_NoSelection_PressDoesNothing()
+    {
+        var h = new Harness();
+
+        h.BuyButton.OnClick!.Invoke();
+
+        Assert.Empty(h.Buys);
+    }
+
+    [Fact]
+    public void ReconciliationRoundTrip_MoneyCreateObjectAndApproachVendorRefresh_FlowThroughExistingMachinery()
+    {
+        // Slice 6.3: verifies the loop end-to-end with synthetic inbound
+        // messages, adding no new owner (research doc §C.4/§A.2 point 4):
+        // (1) a money property update applies to the SAME ClientObjectTable
+        //     the vendor panel reads live for its cost text,
+        // (2) the purchase lands in the player's inventory via the ordinary
+        //     CreateObject merge-upsert (ClientObjectTable.Ingest),
+        // (3) the vendor's post-buy ApproachVendor refresh
+        //     (VendorStateTransitionKind.Refreshed) rebuilds the panel —
+        //     here the bought-out item leaves the vendor's stock entirely
+        //     (the common single-item-purchase case), so the rebuild is
+        //     externally observable: the item leaves the list and the
+        //     selection/buttons clear.
+        var h = new Harness();
+        const uint PurchasedItemGuid = 0x60000900u;
+        h.State.Apply(VendorGuid, Profile(sellRate: 1.0f), new[]
+        {
+            new VendorShopItem(ArmorItemGuid, -1, 2u, "Chainmail", (uint)ItemType.Armor, 200u, 500),
+        });
+        Assert.Equal(1, h.ItemList.GetNumUIItems());
+        Assert.True(h.BuyButton.Enabled);
+
+        h.BuyButton.OnClick!.Invoke();
+        Assert.Single(h.Buys);
+        Assert.False(h.BuyButton.Enabled);
+
+        // (1) Money: PrivateUpdatePropertyInt(CoinValue) — the exact path
+        // ObjectTableWiring's PlayerIntPropertyUpdated handler calls.
+        int newCoinValue = Harness.DefaultPlayerCoinValue - 500;
+        h.Objects.UpdateIntProperty(Harness.PlayerGuid, (uint)PropertyInt.CoinValue, newCoinValue);
+
+        // (2) CreateObject: the purchased item lands in the player's own
+        // inventory — the ordinary Ingest merge-upsert every CreateObject
+        // uses (ObjectTableWiring.ApplyEntitySpawn), landing here with the
+        // player as its container.
+        h.Objects.Ingest(new WeenieData(
+            Guid: PurchasedItemGuid,
+            Name: "Chainmail",
+            Type: ItemType.Armor,
+            WeenieClassId: 2u,
+            IconId: 200u,
+            IconOverlayId: 0u,
+            IconUnderlayId: 0u,
+            Effects: 0u,
+            Value: 500,
+            StackSize: null,
+            StackSizeMax: null,
+            Burden: null,
+            ContainerId: Harness.PlayerGuid,
+            WielderId: 0u,
+            ValidLocations: null,
+            CurrentWieldedLocation: null,
+            Priority: null,
+            ItemsCapacity: null,
+            ContainersCapacity: null,
+            Structure: null,
+            MaxStructure: null,
+            Workmanship: null));
+
+        // (3) ApproachVendor refresh: sold out of the ONLY armor stack, so
+        // the SAME vendor's next snapshot no longer lists it.
+        h.State.Apply(VendorGuid, Profile(sellRate: 1.0f), System.Array.Empty<VendorShopItem>());
+
+        // (4) UseDone completes the reservation.
+        h.ItemInteraction.CompleteUse(0);
+
+        Assert.Equal(newCoinValue, h.Objects.Get(Harness.PlayerGuid)?.Properties.GetInt((uint)PropertyInt.CoinValue));
+        Assert.Equal(Harness.PlayerGuid, h.Objects.Get(PurchasedItemGuid)?.ContainerId);
+        Assert.Equal(0, h.ItemList.GetNumUIItems());
+        Assert.Equal(string.Empty, GetText(h.ItemNameText));
+        Assert.False(h.BuyButton.Enabled);
+    }
 }