in src/global_string.js [59:74]
export async function createGlobalStringSignal(startValue, signalName) {
  const signal = await String(startValue, signalName)
  const updateState = (state, signalName, event) => {
    return SparkAutomergeWrapper.setSignalString(
      state,
      'update value',
      signalName,
      event.newValue
    )
  }
  await GlobalSignal.createGlobalSignal(signal, startValue, signalName, guaranteeStateString, updateState)
  return signal
}