fix(ui): share primary panel placement

Port gmPanelUI's persistent parent placement semantics across Inventory, Character, and Magic while preserving each imported child's content and resize policy. Synchronize typed retained-window handles so drag, switching, close/reopen, and layout persistence all observe one canonical location; keep effect panels independent.

User-verified in normal Release. Release build and all 5,770 tests passed with five intentional skips.

Co-authored-by: OpenAI Codex <codex@openai.com>

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

@@ -1,3 +1,4 @@
+using AcDream.App.UI;
 using AcDream.App.UI.Layout;
 
 namespace AcDream.App.Tests.UI.Layout;
@@ -74,6 +75,71 @@ public sealed class RetailPanelUiControllerTests
         Assert.Equal(2u, controller.ActivePanelId);
     }
 
+    [Fact]
+    public void MainPanels_ShareOneCanonicalPlacementAcrossMoveCloseAndSwitch()
+    {
+        var root = new UiRoot { Width = 1280f, Height = 720f };
+        RetailWindowHandle inventory = Mount(root, WindowNames.Inventory, 40f, 60f);
+        RetailWindowHandle character = Mount(root, WindowNames.Character, 540f, 18f);
+        RetailWindowHandle spellbook = Mount(root, WindowNames.Spellbook, 18f, 18f);
+        using var controller = Create(root);
+        controller.RegisterMainPanel(7u, WindowNames.Inventory, inventory);
+        controller.RegisterMainPanel(11u, WindowNames.Character, character);
+        controller.RegisterMainPanel(13u, WindowNames.Spellbook, spellbook);
+
+        int characterMoves = 0;
+        int spellbookMoves = 0;
+        character.Moved += _ => characterMoves++;
+        spellbook.Moved += _ => spellbookMoves++;
+
+        controller.SetPanelVisibility(7u, visible: true);
+        inventory.MoveTo(312f, 147f);
+
+        Assert.Equal((312f, 147f), (character.Left, character.Top));
+        Assert.Equal((312f, 147f), (spellbook.Left, spellbook.Top));
+        Assert.True(characterMoves > 0);
+        Assert.True(spellbookMoves > 0);
+
+        controller.SetPanelVisibility(11u, visible: true);
+        Assert.False(inventory.IsVisible);
+        Assert.True(character.IsVisible);
+        Assert.Equal((312f, 147f), (character.Left, character.Top));
+
+        controller.SetPanelVisibility(11u, visible: false);
+        controller.SetPanelVisibility(13u, visible: true);
+        Assert.False(character.IsVisible);
+        Assert.True(spellbook.IsVisible);
+        Assert.Equal((312f, 147f), (spellbook.Left, spellbook.Top));
+    }
+
+    [Fact]
+    public void RestorePreviousEffect_DoesNotReplaceMainPanelPlacement()
+    {
+        var root = new UiRoot { Width = 1280f, Height = 720f };
+        RetailWindowHandle inventory = Mount(root, WindowNames.Inventory, 40f, 60f);
+        RetailWindowHandle character = Mount(root, WindowNames.Character, 540f, 18f);
+        RetailWindowHandle effect = Mount(root, WindowNames.PositiveEffects, 900f, 30f);
+        using var controller = Create(root);
+        controller.RegisterMainPanel(7u, WindowNames.Inventory, inventory);
+        controller.RegisterMainPanel(11u, WindowNames.Character, character);
+        controller.Register(4u, WindowNames.PositiveEffects, restorePrevious: true);
+
+        controller.SetPanelVisibility(7u, visible: true);
+        inventory.MoveTo(280f, 120f);
+        controller.SetPanelVisibility(4u, visible: true);
+
+        Assert.Equal((900f, 30f), (effect.Left, effect.Top));
+        Assert.False(inventory.IsVisible);
+        Assert.True(effect.IsVisible);
+
+        controller.SetPanelVisibility(4u, visible: false);
+        Assert.True(inventory.IsVisible);
+        Assert.Equal((280f, 120f), (inventory.Left, inventory.Top));
+
+        controller.SetPanelVisibility(11u, visible: true);
+        Assert.Equal((280f, 120f), (character.Left, character.Top));
+    }
+
     private static RetailPanelUiController Create(Dictionary<string, bool> visible)
         => new(
             name => visible[name],
@@ -87,4 +153,28 @@ public sealed class RetailPanelUiControllerTests
                 visible[name] = false;
                 return true;
             });
+
+    private static RetailPanelUiController Create(UiRoot root)
+        => new(root.IsWindowVisible, root.ShowWindow, root.HideWindow);
+
+    private static RetailWindowHandle Mount(
+        UiRoot root,
+        string name,
+        float left,
+        float top)
+    {
+        var content = new UiPanel { Width = 300f, Height = 500f };
+        return RetailWindowFrame.Mount(
+            root,
+            content,
+            _ => (0u, 0, 0),
+            new RetailWindowFrame.Options
+            {
+                WindowName = name,
+                Left = left,
+                Top = top,
+                Visible = false,
+                ConstrainDragToParent = true,
+            });
+    }
 }