feat: secure trade with other players - wire, RuntimeTradeState, the

authored gmSecureTradeUI window, and both retail open paths

Three-lane research first (docs/research/2026-08-14-trade-lane{A,B,C}):
retail gmSecureTradeUI decode, the byte-exact ACE/decomp/holtburger
three-way wire agreement, and the acdream seam map (which found both
open paths ALREADY classified by the ported policy - OpenSecureTrade on
Use-a-player, StartSecureTrade on drag-item-onto-player with the
DragItemOnPlayerOpensSecureTrade option - dead-ending at a stub toast).

- Core.Net: TradeRequests builders (0x1F6-0x204, retail's CM_Trade
  senders byte-checked against ACE's readers; the ACE-discarded
  AcceptTrade echo carries zero-count item lists - AD-94), corrected +
  completed inbound parsers (0x1FD-0x208; the old AddToTrade parser
  missed the SIDE dword, TradeFailure missed the reason), delegate-hole
  registrars, six WorldSession sends. 10 golden-byte tests.
- Runtime: RuntimeTradeState, the third sibling J-owner (fellowship/
  allegiance shape): session-scoped, clears at generation reset (new
  stage Trade=14), staged teardown stage 11 (Identity/EntityObjects
  shift 12/13, TeardownStageCount 14 - the FA2-era per-stage-flag test
  caught the mapping exactly as designed), combined ownership ledger,
  event routing with ACE's wrong-initiator RegisterTrade landmine
  honored (partner = whichever guid is not mine). 7 conformance tests.
- App: SecureTradeUiController binds the dedicated authored LayoutDesc
  0x2100000D (root 0x1000007A - gmSecureTradeUI::PostInit's exact ids):
  partner name/status/count/grid, the authored 'Trade' accept toggle
  (accept <-> decline withdraw), 'Clear All' (ACE clears BOTH sides -
  surfaced honestly), the X close, drop-on-your-grid staging, per-mode
  accept cues (partner icon's authored Highlight state + Trade button
  Selected latch). Mounted via the vendor recipe (nine-slice chrome,
  hidden until RegisterTrade). ItemInteractionController's two policy
  arms now raise SecureTradeRequested instead of the stub toast; the
  drag path queues the dragged item until the window registers
  (ClientTradeSystem::AttemptToTradeItem @0x0056DF80's shape).

Register: AD-94 (accept-echo zero-count lists), AD-95 (numeric-only
count texts pending template verification).

Suites: App 4,990/3, Core.Net 905, Runtime 1,626 - all green. The
panel itself is user-gate acceptance (two-client connected trade), the
#372-class lesson: fixture-green alone is not acceptance for a mount.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/AcDream.App/UI/RetailUiRuntime.cs

@@ -283,7 +283,10 @@ public sealed record SocialRuntimeBindings(
     Func<uint, RuntimeCommandResult> AllegianceSwear,
     Func<uint, RuntimeCommandResult> AllegianceBreak,
     Func<uint, RuntimeCommandResult> AllegianceKick,
-    Func<bool, RuntimeCommandResult> AllegianceSetUpdateSubscription);
+    Func<bool, RuntimeCommandResult> AllegianceSetUpdateSubscription,
+    // Secure trade (2026-08-14): the third sibling J-owner's borrowed view.
+    // Trailing/optional per the established compatibility convention.
+    AcDream.Runtime.Gameplay.IRuntimeTradeView? Trade = null);
 
 public sealed record InventoryRuntimeBindings(
     ClientObjectTable Objects,
@@ -478,6 +481,7 @@ public sealed class RetailUiRuntime : IDisposable
         MountInventory();
         MountExternalContainer();
         MountVendor();
+        MountSecureTrade();
         MountItemCooldowns();
         Host.WindowManager.WindowVisibilityChanged += OnWindowVisibilityChanged;
         BindToolbarPanelButtons();
@@ -607,6 +611,7 @@ public sealed class RetailUiRuntime : IDisposable
         LinkStatusUiController?.Tick();
         IndicatorBarController?.Tick();
         JumpPowerbarController?.Tick();
+        SecureTradeController?.Tick();
         SelectedObjectController?.Tick(deltaSeconds);
         ExternalContainerController?.Tick();
         SocialPanelController?.Tick();
@@ -3470,6 +3475,102 @@ public sealed class RetailUiRuntime : IDisposable
         Console.WriteLine("[M4] retail vendor browse panel mounted from LayoutDesc 0x21000012.");
     }
 
+    /// <summary>The mounted secure-trade window's controller — null until
+    /// <see cref="MountSecureTrade"/> runs (or when the trade view/layout is
+    /// unavailable).</summary>
+    public Layout.SecureTradeUiController? SecureTradeController { get; private set; }
+
+    private void MountSecureTrade()
+    {
+        if (_bindings.Social.Trade is not { } tradeView)
+        {
+            Console.WriteLine("[M4] secure trade: no runtime trade view bound.");
+            return;
+        }
+
+        ImportedLayout? layout;
+        lock (_bindings.Assets.DatLock)
+        {
+            layout = LayoutImporter.Import(
+                _bindings.Assets.Dats,
+                Layout.SecureTradeUiController.LayoutId,
+                Layout.SecureTradeUiController.RootId,
+                _bindings.Assets.ResolveSprite,
+                _bindings.Assets.DefaultFont,
+                _bindings.Assets.ResolveFont);
+        }
+        if (layout is null)
+        {
+            Console.WriteLine(
+                "[M4] secure trade: LayoutDesc 0x2100000D root 0x1000007A not found.");
+            return;
+        }
+
+        var bus = _bindings.Options.CommandBus();
+        Layout.SecureTradeUiController? controller =
+            Layout.SecureTradeUiController.Bind(
+                layout,
+                new Layout.SecureTradeUiController.Bindings(
+                    Trade: tradeView,
+                    Objects: _bindings.Inventory.Objects,
+                    ResolveIcon: _bindings.Inventory.ResolveIcon,
+                    OpenTrade: partner => bus.Publish(
+                        new OpenTradeNegotiationsRuntimeCmd(partner)),
+                    CloseTrade: () => bus.Publish(
+                        new CloseTradeNegotiationsRuntimeCmd()),
+                    AddToTrade: item => bus.Publish(
+                        new AddToTradeRuntimeCmd(item)),
+                    AcceptTrade: (selfAccepted, partnerAccepted, partner) =>
+                        bus.Publish(new AcceptTradeRuntimeCmd(
+                            partner, selfAccepted, partnerAccepted)),
+                    DeclineTrade: () => bus.Publish(new DeclineTradeRuntimeCmd()),
+                    ResetTrade: () => bus.Publish(new ResetTradeRuntimeCmd()),
+                    SetWindowVisible: visible =>
+                    {
+                        if (visible) Host.ShowWindow(WindowNames.SecureTrade);
+                        else Host.HideWindow(WindowNames.SecureTrade);
+                    }));
+        if (controller is null)
+        {
+            Console.WriteLine("[M4] secure trade: required authored grids are missing.");
+            return;
+        }
+
+        UiElement root = layout.Root;
+        RetailWindowFrame.Mount(
+            Host.Root,
+            root,
+            _bindings.Assets.ResolveSprite,
+            new RetailWindowFrame.Options
+            {
+                WindowName = WindowNames.SecureTrade,
+                // Root 0x1000007A authors content only (the in-screen copy's
+                // bevel lives in LayoutDesc 0x21000005, not here) — the
+                // shared nine-slice frame surrounds it, same as the vendor.
+                Chrome = RetailWindowChrome.NineSlice,
+                Left = MathF.Max(0f, (Host.Root.Width - root.Width) * 0.5f),
+                Top = MathF.Max(0f, (Host.Root.Height - root.Height) * 0.5f),
+                ContentWidth = root.Width,
+                ContentHeight = root.Height,
+                MinWidth = root.Width,
+                MinHeight = root.Height,
+                Visible = false,
+                ResizeX = false,
+                ResizeY = false,
+                ConstrainDragToParent = true,
+                ConstrainResizeToParent = true,
+            });
+
+        SecureTradeController = controller;
+        Host.WindowManager.AttachController(WindowNames.SecureTrade, controller);
+        // Both retail open paths (Use-on-player, drag-item-on-player) —
+        // raised by ItemInteractionController's policy execution arms.
+        _bindings.Inventory.ItemInteraction.SecureTradeRequested +=
+            controller.RequestSecureTrade;
+        Console.WriteLine(
+            "[M4] retail secure trade panel mounted from LayoutDesc 0x2100000D.");
+    }
+
     private void MountItemCooldowns()
     {
         ItemCooldownAssets? assets;
@@ -3506,6 +3607,11 @@ public sealed class RetailUiRuntime : IDisposable
                 _characterSheetSubscription?.Dispose();
                 Host.WindowManager.WindowVisibilityChanged -= OnWindowVisibilityChanged;
                 WindowOpacity.Dispose();
+                if (SecureTradeController is { } trade)
+                {
+                    _bindings.Inventory.ItemInteraction.SecureTradeRequested -=
+                        trade.RequestSecureTrade;
+                }
             },
             () => _itemConfirmationController?.Dispose(),
             () => _gameplayConfirmationController?.Dispose(),