inbuxa:ReportExport/set creates {reportId, from?, to?}: the report built
for that period (its last full one by default, at most 90 days back, as
far as metrics are kept) as a ZIP of summary.txt and the section CSVs,
stored as an upload, mailing nobody. Reading needs sysScheduledReportGet,
as seeing the report does; a tenant administrator downloads only their
own; every download is in the audit log. A download doesn't move the
deliverability baseline the next mail compares with.