optional preview frame

tests/RenderCadenceCompositorAppConfigProviderTests.cpp

@@ -36,6 +36,7 @@ std::filesystem::path WriteConfigFixture()
 		<< "  \"outputFrameRate\": \"60\",\n"
 		<< "  \"autoReload\": false,\n"
 		<< "  \"maxTemporalHistoryFrames\": 8,\n"
+		<< "  \"previewEnabled\": true,\n"
 		<< "  \"previewFps\": 24,\n"
 		<< "  \"enableExternalKeying\": true\n"
 		<< "}\n";
@@ -66,6 +67,7 @@ void TestLoadsRuntimeHostConfig()
 	Expect(config.outputFrameRate == "60", "output frame rate loads");
 	Expect(!config.autoReload, "auto reload loads");
 	Expect(config.maxTemporalHistoryFrames == 8, "history length loads");
+	Expect(config.previewEnabled, "preview enabled toggle loads");
 	Expect(config.previewFps == 24.0, "preview fps loads");
 	Expect(config.deckLink.externalKeyingEnabled, "external keying loads");
 
@@ -91,6 +93,15 @@ void TestCommandLineOverrides()
 	Expect(config.http.preferredPort == 8282, "port CLI override applies");
 }
 
+void TestPreviewDefaultsAreOptIn()
+{
+	using namespace RenderCadenceCompositor;
+
+	const AppConfig config = DefaultAppConfig();
+	Expect(!config.previewEnabled, "preview is disabled by default");
+	Expect(config.previewFps == 30.0, "preview fps default is 30");
+}
+
 void TestHelpers()
 {
 	using namespace RenderCadenceCompositor;
@@ -118,6 +129,7 @@ int main()
 {
 	TestLoadsRuntimeHostConfig();
 	TestCommandLineOverrides();
+	TestPreviewDefaultsAreOptIn();
 	TestHelpers();
 
 	if (gFailures != 0)