If you want to go full circle you can send the ⌘-C and ⌘-V key events before/after they query. This will just send selected text and replace this with answer. I prefer not to do that, since queries are quite slow and I rarely block waiting for round trip. I also use vim and vim mode in lot's of apps, so replace works differently there.

I prefer to use clipboard as the exchange place. I select text, copy it, then query the service. Once the query completes I can see the answer in popup and can paste it to my current editing place.

This is the code:

  local hyper = {"cmd", "alt", "ctrl"}

  hs.hotkey.bind(hyper, "Y", function()
    local url = "https://api.openai.com/v1/completions"
    local api_key = "..."

    local headers = {
      authorization="Bearer " .. api_key,
      ["content-type"]="application/json",
      accept="application/json"
    }

    -- hs.eventtap.keyStroke({"cmd"}, "c")

    local message = hs.pasteboard.readString()

    local data = {
      prompt=message,
      model="text-davinci-003",
      max_tokens=32,
      temperature=0
    }

    hs.notify.new({title="OpenAI query", informativeText=message}):send()

    hs.http.asyncPost(url, hs.json.encode(data), headers, function(status, body, headers)
      local response = hs.json.decode(body)
      local answer = response["choices"][1]["text"]

      print(body)

      hs.notify.new({title="OpenAI response", informativeText=answer}):send()
      hs.pasteboard.writeObjects(answer)
      -- hs.eventtap.keyStroke({"cmd"}, "v")
    end)
  end)