should be it

external/duckdb/extension/demo_capi/capi_demo.cpp

@@ -0,0 +1,24 @@
+#include "add_numbers.h"
+#include "duckdb_extension.h"
+
+DUCKDB_EXTENSION_ENTRYPOINT(duckdb_connection connection, duckdb_extension_info info, duckdb_extension_access *access) {
+
+	// Register a demo function
+	RegisterAddNumbersFunction(connection);
+
+#ifdef DUCKDB_EXTENSION_API_VERSION_UNSTABLE
+	// Test using the unstable API
+	duckdb_arrow result;
+	auto api_result = duckdb_query_arrow(connection, "SELECT 1 as a", &result);
+
+	if (api_result != duckdb_state::DuckDBSuccess) {
+		access->set_error(info, "Arrow Query failed during initialization");
+		return false;
+	}
+
+	duckdb_destroy_arrow(&result);
+#endif
+
+	// Return true to indicate succesful initialization
+	return true;
+}