in src/spark_automerge_wrapper.js [218:230]
function processMessage(state, syncStates, peerId, msg) {
  const [metaData, syncMessage] = decodeMessage(msg)
  const sourcePeerId = metaData.s
  const targetPeerId = metaData.t
  if (targetPeerId && targetPeerId !== peerId) {
    return [state, null, true]
  }
  const ret = processSyncMessage(state, syncStates, sourcePeerId, syncMessage)
  ret.push(false)
  return ret
}