A snapshot: name, view-order columns, view-order rows, and the
visual specification when the host exposes one.
Throws
Whatever getSummaryColumnsInfoAsync or getPageAsync throws. The
reader is always released first; the caller decides whether a failed read
means keeping the previous figure.
Read everything one worksheet contributes to the figure.
The column info call is made first and outside the queue — it opens no reader — so the view order is known before any pagination starts.