Function user_storage_key

perro_source/io_stack/perro_io/src/asset_io.rs:228–230

(app_name: &str, relative_path: &str)

    validate_dlc_name(name)?;
    let root = root.as_ref().to_path_buf();
    if !root.exists() {
        return Err(io::Error::new(
            io::ErrorKind::NotFound,
            format!("dlc disk root not found: {}", root.display()),
        ));
    }