diff --git a/src/AcDream.App/Rendering/GameWindow.cs b/src/AcDream.App/Rendering/GameWindow.cs
index 2e26a360..1944137d 100644
--- a/src/AcDream.App/Rendering/GameWindow.cs
+++ b/src/AcDream.App/Rendering/GameWindow.cs
@@ -1794,6 +1794,36 @@ public sealed class GameWindow : IDisposable
             _uiHost.Root.AddChild(panel);
             Console.WriteLine("[D.2b] retail UI active — vitals panel from vitals.xml markup.");
 
+            // Phase D.2b — LayoutDesc importer A/B harness. When ACDREAM_RETAIL_UI_IMPORTER=1,
+            // build the SAME vitals window (0x2100006C) data-driven from the dat and place it beside
+            // the hand-authored one so the two can be compared pixel-for-pixel before the importer
+            // becomes the default. The hand-authored path above is untouched.
+            if (_options.RetailUiImporter)
+            {
+                AcDream.App.UI.Layout.ImportedLayout? imported;
+                lock (_datLock)
+                    imported = AcDream.App.UI.Layout.LayoutImporter.Import(
+                        _dats!, 0x2100006Cu, ResolveChrome, vitalsDatFont);
+                if (imported is not null)
+                {
+                    AcDream.App.UI.Layout.VitalsController.Bind(imported,
+                        healthPct:   () => _vitalsVm!.HealthPercent,
+                        staminaPct:  () => _vitalsVm!.StaminaPercent ?? 0f,
+                        manaPct:     () => _vitalsVm!.ManaPercent ?? 0f,
+                        healthText:  () => (_vitalsVm!.HealthCurrent, _vitalsVm.HealthMax) is (uint c, uint m) ? $"{c}/{m}" : "",
+                        staminaText: () => (_vitalsVm!.StaminaCurrent, _vitalsVm.StaminaMax) is (uint c, uint m) ? $"{c}/{m}" : "",
+                        manaText:    () => (_vitalsVm!.ManaCurrent, _vitalsVm.ManaMax) is (uint c, uint m) ? $"{c}/{m}" : "");
+                    // Offset beside the hand-authored window (at x=10) for an A/B visual comparison.
+                    imported.Root.Left = 200; imported.Root.Top = 30;
+                    _uiHost.Root.AddChild(imported.Root);
+                    Console.WriteLine("[D.2b] importer vitals window active (A/B vs hand-authored).");
+                }
+                else
+                {
+                    Console.WriteLine("[D.2b] importer vitals: LayoutDesc 0x2100006C not found.");
+                }
+            }
+
             // Retail chat window — a draggable/resizable nine-slice frame hosting a
             // scrollable transcript (UiChatView). Read-only + wheel-scroll for now;
             // drag-select + Ctrl+C copy land in the next D.2b sub-step. A dedicated
diff --git a/src/AcDream.App/RuntimeOptions.cs b/src/AcDream.App/RuntimeOptions.cs
index 9be7601d..bff1f885 100644
--- a/src/AcDream.App/RuntimeOptions.cs
+++ b/src/AcDream.App/RuntimeOptions.cs
@@ -41,6 +41,7 @@ public sealed record RuntimeOptions(
     bool DumpLiveSpawns,
     int? LegacyStreamRadius,
     bool RetailUi,
+    bool RetailUiImporter,
     string? AcDir)
 {
     /// <summary>
@@ -85,6 +86,7 @@ public sealed record RuntimeOptions(
             // top of the quality preset's radii. Null when unset or invalid.
             LegacyStreamRadius:  TryParseNonNegativeInt(env("ACDREAM_STREAM_RADIUS")),
             RetailUi:            IsExactlyOne(env("ACDREAM_RETAIL_UI")),
+            RetailUiImporter:    IsExactlyOne(env("ACDREAM_RETAIL_UI_IMPORTER")),
             AcDir:               NullIfEmpty(env("ACDREAM_AC_DIR")));
     }
 
diff --git a/tests/AcDream.App.Tests/RuntimeOptionsRetailUiTests.cs b/tests/AcDream.App.Tests/RuntimeOptionsRetailUiTests.cs
index b18590ae..9c6b88a2 100644
--- a/tests/AcDream.App.Tests/RuntimeOptionsRetailUiTests.cs
+++ b/tests/AcDream.App.Tests/RuntimeOptionsRetailUiTests.cs
@@ -25,4 +25,29 @@ public class RuntimeOptionsRetailUiTests
         Assert.False(opts.RetailUi);
         Assert.Null(opts.AcDir);
     }
+
+    [Fact]
+    public void Parse_ReadsRetailUiImporter_WhenSetToOne()
+    {
+        var env = new Dictionary<string, string?>
+        {
+            ["ACDREAM_RETAIL_UI_IMPORTER"] = "1",
+        };
+        var opts = RuntimeOptions.Parse("dats", k => env.GetValueOrDefault(k));
+        Assert.True(opts.RetailUiImporter);
+    }
+
+    [Fact]
+    public void Parse_DefaultsRetailUiImporterOff_WhenUnsetOrOtherValue()
+    {
+        // Unset → false.
+        Assert.False(RuntimeOptions.Parse("dats", _ => null).RetailUiImporter);
+
+        // Non-"1" values → false (mirrors RetailUi / other IsExactlyOne flags).
+        var envOther = new Dictionary<string, string?>
+        {
+            ["ACDREAM_RETAIL_UI_IMPORTER"] = "true",
+        };
+        Assert.False(RuntimeOptions.Parse("dats", k => envOther.GetValueOrDefault(k)).RetailUiImporter);
+    }
 }