Stream Presence

The rail's live wire — presence pushed, not polled.

ONE CONNECTION PER PERSON, NOT FIFTEEN REQUESTS A MINUTE PER TAB. The poll this replaces was correct and expensive in the same breath: it asked "is anything working" every four seconds forever, and was still up to four seconds late with the answer. The browser keeps GET /presence as the opening read and the fallback when a stream cannot be held, so nothing here is load-bearing for correctness — it is the difference between a light that is right and a light that is right IMMEDIATELY.