feat: harden isolated Tornado test workflow

tests/MBN_STOCK_WEBVIEW.Playout.Tests/PlayoutOptionsLoaderTests.cs

@@ -117,6 +117,26 @@ public sealed class PlayoutOptionsLoaderTests
         Assert.True(options.TrustedLiveOutputEnabled);
     }
 
+    [Fact]
+    public void LoadFileOnly_IgnoresEnvironmentForReproducibleExplicitDiagnostics()
+    {
+        using var environment = ClearedEnvironment()
+            .Set("MBN_STOCK_PLAYOUT_MODE", "Live")
+            .Set("MBN_STOCK_PLAYOUT_HOST", "sensitive-host");
+        using var file = TemporaryJsonFile.Create(
+            """
+            {
+              "mode": "Test",
+              "host": "127.0.0.1"
+            }
+            """);
+
+        var options = PlayoutOptionsLoader.LoadFileOnly(file.Path);
+
+        Assert.Equal(PlayoutMode.Test, options.Mode);
+        Assert.Equal("127.0.0.1", options.Host);
+    }
+
     [Fact]
     public void Load_InvalidJson_ReturnsOnlySafeConfigurationMessage()
     {