Announces a supervised wrapper's start fact and its end fact from a process of its own.

A wrapper, such as macula_stream_sink, calls start/2 once its operation has begun. The announcer monitors the wrapper, publishes the start fact, and waits for the wrapper to hand over its end payload with announce_end/2, which it publishes under the end topic. A wrapper that goes down before it hands over its end, for example because it was killed, has its end fact published for it, with the end fields plus outcome failed and the reason it went down for. Either way exactly one end fact goes out.

An end fact carries its reason's name, from macula_reason_name, and none of the reason's terms; a reason that is more than a name goes to the local log, printed within bounds.

Publishing never fails or ends the wrapper: a publish that raises or returns anything but ok is logged, and the announcer goes on. The publish function must return in bounded time, since the announcer outlives its wrapper for as long as its last publish takes; macula:publish/4 returns within 5.5 seconds. The announcer touches nothing but its publish function, and it ends once it has published the end fact.