Function list_page_in 

pub fn list_page_in(
    store: &Mutex<CursorStore>,
    req: &FsListReq,
    now: Instant,
) -> FsListResult

One page of fs.list. A failure to open the directory is an Ok answer with error set, never an Err (spec §9: a denied folder must never look empty, and must never fail the pane).