The original middleware

index.ts

type Conv = DialogflowConversation<TabletopAudioSession>

app.middleware(async (conv: Conv) => {
  await cacheResults(conv)
})

async function cacheResults(conv: Conv) {
  if (!conv.data.json) {
    const response = await fetch(tabletopAudioUrl)
    const json: TabletopAudioResponse = await response.json()
    conv.data.json = json
  }
}