test(app)+docs: CC4 REVIEW-CLOSED — R5 chargen root extent pinned by observation

The final CC4 re-review closed R1-R4 (the fixed-canvas arbiter, headless
create-gate proof, #402 filing) and left one residual: the arbiter's
mismatch-throw makes 'both char-select screens author 800x600' a crash
premise on the exact user-gate path (ACDREAM_OPEN_CHARGEN=1 ->
char-management declares -> chargen declares on top), and only
char-management's extent was DAT-pinned. The chargen live-DAT probe now
pins the root at 800x600 the same way — measured against the installed
DAT (passes 7/7), not inferred. Ledger row flipped to REVIEW-CLOSED with
real shas.

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

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

@@ -43,6 +43,20 @@ public sealed class CharacterCreationLiveDatTests
             CharacterCreationUiController.RootElementId,
             screen.Root.DatElementId);
 
+        // CC4 re-review R5: the fixed-canvas arbiter THROWS if two concurrent
+        // screens declare different sizes, and char-management's root is
+        // DAT-pinned at 800x600 (CharacterManagementLiveDatTests). Chargen
+        // declares on top of it on the exact user-gate path, so its authored
+        // extent must be pinned too — an unequal extent is now a crash at
+        // Open(), not a cosmetic drift. Observe, don't infer (C4 closeout).
+        ElementInfo rootInfo = Assert.IsType<ElementInfo>(
+            LayoutImporter.ImportInfos(
+                dats,
+                layoutId,
+                CharacterCreationUiController.RootElementId));
+        Assert.Equal(800f, rootInfo.Width);
+        Assert.Equal(600f, rootInfo.Height);
+
         Assert.IsAssignableFrom<UiElement>(
             screen.FindElement(CharacterCreationUiController.ProgressBarElementId));
         AssertButton(screen, CharacterCreationUiController.BackElementId);