assertTrue(ex instanceof IOException, "Should be an IOException (checked)");
    }

    @ParameterizedTest(name = "Message-only ctor preserves message: [{0}]")
    @MethodSource("messages")
    void messageConstructor_setsMessageAndNullCause(String message) {
        // Arrange & Act
        SMBProtocolDowngradeException ex = new SMBProtocolDowngradeException(message);

        // Assert - message preserved, cause null