Every story the desk has followed across three signals or more, ranked each Thursday: the longest first, then the one that moved last. Each arc is a Record: the outlets, in order, with the receipts.
One story gets one signal; when the story moves, the desk publishes the development and links it both ways. An arc is what that leaves behind: every outlet that reported it, in the order they did, with a verbatim receipt for each. This is where the arcs live. Single signals stay on their channel pages until a second report makes them a story.