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let estimate: WebAPI.StorageAPI.storageManager => promise< WebAPI.StorageAPI.storageEstimate,>
let getDirectory: WebAPI.StorageAPI.storageManager => promise< WebAPI.FileAPI.fileSystemDirectoryHandle,>
let persist: WebAPI.StorageAPI.storageManager => promise<bool>
let persisted: WebAPI.StorageAPI.storageManager => promise<bool>