Glossary
Engagement dedup
The rule that a post you have already engaged with never comes back — within that exchange.
Within one exchange, a post you have engaged with never reappears, and neither does a queue you have already worked. The exclusion is per-post and per-queue, and it does not expire.
It is NOT cross-exchange, and this site said for a long time that it was. Commenting on a post does not remove it from your saves or shares queue: each exchange keeps its own history and checks only that. If the phrase "cross-exchange dedup" brought you here, that is the correction.
Follows are deduped permanently by nature — you can only follow someone once. Story views are deduped pairwise per calendar month, because a permanent block there would burn a useful pair after a single view.
This is why an exchange can feel quiet for an established account: it has already seen a great deal of what that exchange has, and the engine will not recycle it.
See also