Make sure we describe the importance of introduce replay detection accurately

See analysis at arti#725 (comment 2960032)

If this is right, we should mention it in the spec.

added Backlog label

assigned to @nickm

added Next label and removed Backlog label

added Doing label and removed Next label

added Needs Review label and removed Doing label

mentioned in merge request !349 (merged)

added 30m of time spent

mentioned in commit 3d46c77e

closed with merge request !349 (merged)

closed with commit d1daab72