diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index bba630e7..7c6bfd22 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -2137,6 +2137,19 @@ public sealed class GameWindow : IDisposable
                     }
                 }
             }
+
+            // Phase D.2b-A — placeholder inventory window. Starts HIDDEN; F12
+            // (InputAction.ToggleInventoryPanel) reveals it via the UiRoot window
+            // manager. Throwaway scaffolding: Sub-phase B replaces the body with the
+            // real gmInventoryUI (0x21000023) nested layout, keeping the same name.
+            var inventoryWindow = new AcDream.App.UI.UiNineSlicePanel(ResolveChrome)
+            {
+                Left = 220, Top = 120, Width = 320, Height = 400,
+                Visible = false,
+            };
+            _uiHost.Root.AddChild(inventoryWindow);
+            _uiHost.RegisterWindow(AcDream.App.UI.WindowNames.Inventory, inventoryWindow);
+            Console.WriteLine("[D.2b-A] placeholder inventory window registered (F12 toggles).");
         }
 
         // Phase N.4+N.5 — WB rendering pipeline foundation. The modern path is
@@ -11420,6 +11433,13 @@ public sealed class GameWindow : IDisposable
 
         switch (action)
         {
+            case AcDream.UI.Abstractions.Input.InputAction.ToggleInventoryPanel:
+                // Retail F12 (rebindable). Gated upstream by WantsKeyboard, so it
+                // does not fire while the chat input holds focus. Null _uiHost =
+                // retail UI off (ACDREAM_RETAIL_UI unset) → no-op.
+                _uiHost?.ToggleWindow(AcDream.App.UI.WindowNames.Inventory);
+                break;
+
             case AcDream.UI.Abstractions.Input.InputAction.AcdreamToggleDebugPanel:
                 foreach (var panel in EnumerateDebugPanel())
                 {
diff --git a/src/AcDream.App/UI/UiHost.cs b/src/AcDream.App/UI/UiHost.cs
index 718d5cbd..8e4c66f3 100644
--- a/src/AcDream.App/UI/UiHost.cs
+++ b/src/AcDream.App/UI/UiHost.cs
@@ -103,6 +103,14 @@ public sealed class UiHost : System.IDisposable
         _                  => UiMouseButton.Left,
     };
 
+    // ── Window manager forwarders (delegate to UiRoot) ─────────────────
+
+    /// <summary>Register a top-level window for Show/Hide/Toggle. See <see cref="UiRoot.RegisterWindow"/>.</summary>
+    public void RegisterWindow(string name, UiElement window) => Root.RegisterWindow(name, window);
+
+    /// <summary>Toggle a registered window's visibility; returns the new IsVisible.</summary>
+    public bool ToggleWindow(string name) => Root.ToggleWindow(name);
+
     public void Dispose()
     {
         TextRenderer.Dispose();