feat: align legacy operator and playout behavior

tests/MBN_STOCK_WEBVIEW.Playout.Tests/PlayoutSceneCompositionFactoryTests.cs

@@ -15,6 +15,33 @@ public sealed class PlayoutSceneCompositionFactoryTests
         Assert.Null(result.BackgroundAssetPath);
     }
 
+    [Theory]
+    [InlineData(0)]
+    [InlineData(6)]
+    [InlineData(19)]
+    public void Fade_AcceptsOriginalDissolveComboIndexRange(int fadeDuration)
+    {
+        var result = PlayoutSceneCompositionFactory.Create(new PlayoutOptions
+        {
+            LegacySceneFadeDuration = fadeDuration
+        });
+
+        Assert.Equal(fadeDuration, result.FadeDuration);
+    }
+
+    [Theory]
+    [InlineData(-1)]
+    [InlineData(20)]
+    [InlineData(60)]
+    public void Fade_RejectsValuesOutsideOriginalDissolveComboIndexRange(int fadeDuration)
+    {
+        Assert.Throws<PlayoutConfigurationException>(() =>
+            PlayoutSceneCompositionFactory.Create(new PlayoutOptions
+            {
+                LegacySceneFadeDuration = fadeDuration
+            }));
+    }
+
     [Fact]
     public void TrustedRelativeVideo_IsVerifiedEvenInDryRun()
     {
@@ -92,4 +119,44 @@ public sealed class PlayoutSceneCompositionFactoryTests
                 new PlayoutOptions { SceneDirectory = scenes.Path },
                 fadeDuration: 6));
     }
+
+    [Fact]
+    public void LegacyStartupDefault_UsesCutsVideo_NotSiblingBackgroundRoot()
+    {
+        using var scenes = TemporarySceneDirectory.Create(
+            "5001.t2s",
+            PlayoutSceneCompositionFactory.LegacyStartupDefaultBackgroundAssetPath);
+        var backgroundRoot = Path.Combine(Directory.GetParent(scenes.Path)!.FullName, "배경");
+        Directory.CreateDirectory(backgroundRoot);
+        File.WriteAllText(
+            Path.Combine(
+                backgroundRoot,
+                PlayoutSceneCompositionFactory.LegacyDefaultBackgroundFileName),
+            "trusted F2/F3 background");
+
+        var result = PlayoutSceneCompositionFactory.CreateLegacyStartupDefault(
+            new PlayoutOptions { SceneDirectory = scenes.Path },
+            fadeDuration: 6);
+
+        Assert.Equal(@"video\기본.vrv", result.BackgroundAssetPath);
+        Assert.Equal(PlayoutAssetRoot.SceneDirectory, result.BackgroundAssetRoot);
+    }
+
+    [Fact]
+    public void LegacyStartupDefault_MissingCutsVideo_FailsEvenWhenSiblingDefaultExists()
+    {
+        using var scenes = TemporarySceneDirectory.Create("5001.t2s");
+        var backgroundRoot = Path.Combine(Directory.GetParent(scenes.Path)!.FullName, "배경");
+        Directory.CreateDirectory(backgroundRoot);
+        File.WriteAllText(
+            Path.Combine(
+                backgroundRoot,
+                PlayoutSceneCompositionFactory.LegacyDefaultBackgroundFileName),
+            "trusted F2/F3 background");
+
+        Assert.Throws<PlayoutConfigurationException>(() =>
+            PlayoutSceneCompositionFactory.CreateLegacyStartupDefault(
+                new PlayoutOptions { SceneDirectory = scenes.Path },
+                fadeDuration: 6));
+    }
 }