Run events

type ViewState = {
  active: Set<string>
  settled: Set<string>
}

function reduce(state: ViewState, event: { kind: string; [key: string]: unknown }) {
  switch (event.kind) {
    case 'task_started':
      state.active.add(String(event.task_id))
      break
    case 'task_completed':
      state.active.delete(String(event.task_id))
      state.settled.add(String(event.task_id))
      break
    default:
      telemetry.debug('unrendered event', event.kind)
  }
}