ADMIN

Lists a campaign's vouchers, newest first is not guaranteed — codes are
returned in key order, so treat the sequence as stable but not chronological
and page through it with the supplied cursor.

campaign_id is required. The table is keyed by campaign, and a campaign can
hold millions of codes, so there is no unscoped listing.

Filtering by tag returns exactly one batch's codes. Vouchers created before
batching existed carry no tag and never appear under a tag filter.