@Nested
    @DisplayName("Lifecycle and exception mapping")
    class LifecycleAndExceptions {

        @Test
        @DisplayName("open() acquires handle and closes it")
        void openDelegatesEnsureOpenAndCloses() throws Exception {
            SmbFileInputStream in = newStream();
            in.open();
            // ensureOpen returns acquired handle; try-with-resources must close it