Rht
data class RhtWrite(val installed: RhtNode? = null, val revived: RhtNode? = null, val superseded: RhtNode? = null)
RhtWrite is what Rht.set reports back.
installed is the node the write put in the map, absent when the write lost LWW and changed nothing. Its size is what enters docSize.live.
revived is a tombstone this write replaced. It was registered as garbage when it was removed, so the caller re-registers the pair to cancel that registration: it is no longer collectable, it is simply gone.
superseded is a LIVE node this write replaced. RHT overrides immutably, so the old node is dropped with no tombstone and nothing to collect, but its bytes were counted in docSize.live and have to leave it.