- the registered view keeps the console that started it; Println, Printf
and status lines go above it only from that console, other consoles
write to their own writers (bonfire.PrintAbove still reaches any view)
- runLive claims the single live slot by check and set under liveMu and
reports when it could not, so the widget prints plain lines
- unregister, finish and wait run deferred, so a panic in work leaves no
registration behind and still propagates (WR-02)
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