feat(render): implement Campaign AR and terrain fidelity

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

@@ -431,4 +431,47 @@ public sealed class OptionPageModelTests
         Assert.Equal(0, flushCount); // NO AfterApply publication on a seed
         Assert.Equal(1, gatingCount); // Apply/Reset ghosting re-evaluated
     }
+
+    [Fact]
+    public void RemoveTail_DetachesRowsAndPageNotifyOwnership()
+    {
+        var page = new OptionPage();
+        var retained = new BoolOptionRow(false, false);
+        var removed = new BoolOptionRow(false, false);
+        int notifications = 0;
+        page.OnOptionChanged = () => notifications++;
+        page.Register(retained);
+        page.Register(removed);
+
+        page.RemoveTail(1);
+        notifications = 0;
+        removed.SetCurrentValue(true);
+
+        Assert.Single(page.Rows);
+        Assert.Same(retained, page.Rows[0]);
+        Assert.Equal(0, notifications);
+        Assert.False(page.Changed);
+    }
+
+    [Fact]
+    public void Defaults_IsSafeWhenAnEarlierRowReplacesTheDynamicTail()
+    {
+        var page = new OptionPage();
+        int removedApplyCount = 0;
+        var pack = new BoolOptionRow(
+            initial: true,
+            defaultValue: false,
+            apply: _ => page.RemoveTail(1));
+        var dynamic = new BoolOptionRow(
+            initial: false,
+            defaultValue: true,
+            apply: _ => removedApplyCount++);
+        page.Register(pack);
+        page.Register(dynamic);
+
+        page.Defaults();
+
+        Assert.Single(page.Rows);
+        Assert.Equal(0, removedApplyCount);
+    }
 }