transcribe: refactor in anticipation of EventSource client
transcribe: refactor in anticipation of EventSource client

shaunstanislaus/magic-wormhole,warner/magic-wormhole,warner/magic-wormhole,idanyelin/magic-wormhole,warner/magic-wormhole,barseghyanartur/magic-wormhole,warner/magic-wormhole,negativo/magic-wormhole,david415/magic-wormhole