Groups withdrawn StateNotifications by their producing commit's hex
digest, so a rewind site can emit exactly one StateInvalidatedIngestResult per superseded commit (D-11) instead of one
per notification. Preserves each group's first-seen order; iteration order
of groups follows first appearance in notifications.
Groups withdrawn StateNotifications by their producing commit's hex digest, so a rewind site can emit exactly one StateInvalidatedIngestResult per superseded commit (D-11) instead of one per notification. Preserves each group's first-seen order; iteration order of groups follows first appearance in
notifications.