Function with

native/watchos/src/scene.rs:160–166

(f: F)

});

fn with<F, R>(f: F) -> R where F: FnOnce(&mut Inner) -> R {
    let mut g = INNER.lock().unwrap();
    if g.nodes.is_empty() {
        g.nodes.push(None);  // sentinel at index 0
    }
    f(&mut *g)
}

// ============================================================
// Mutations — called from bloom_scene_* FFI in lib.rs