Trying to understand async/await in lambda

Thanks to some great help here I have made some progress un understanding the problem I'm trying to solve, but I'm still missing something fundamental.

My use case is an existing lambda-based rules engine, written in Node. The rules in a set generally use results from evaluation of earlier rules, so executing them in sequence, synchronously, makes most sense. I can see how it might be possible to fire off separate asynchronous function calls for everything and then somehow clear up the mess afterwards, potentially re-calling those that failed due to missing data but this would be a nightmare.

So what I'm trying to do is insert an async call in what is currently an exclusively synchronous architecture, and I'm not even sure if this is possible in JS/Node. Any advice gratefully appreciated! This might be a Javascript or even a Node.js question rather than an AWS Lambda one, but from my research the way that asynchronous functions are scheduled does seem to be unique to this combination so I thought I'd start here!

It would be great to get to the bottom of this though ... I'd feel less dumb :)

This is a stripped-back example that shows what I'd like to achieve, inserting an async call to ChatGPT:

const { Configuration, OpenAIApi } = require("openai");

exports.handler = async function(event, context, callback) {

    var output;

	try {
		output = await makeSentence(event.prompt);
		console.log('output: ' + output);
	}
	catch (e){
		output = e.message;
	}

	let response = {
		statusCode: 200,
		headers: { "Content-type" : "application/json" },
		body: JSON.stringify(output)
	};

	return response;
};

async function makeSentence(prompt)
{
	const rule1 = getOpening();                     // existing sync call
	const rule2 = await getMiddle(prompt);          // new async call
	const rule3 = getClosing(rule1 + ' ' + rule2);  // existing sync call
	
        // assemble all the results and return the final result
	return rule3;
}

function getOpening()
{
	const greeting = [ 'Hello', 'Hi', 'Greetings'];
	const random = Math.floor(Math.random() * greeting.length);
	
	return '<sentence>' + greeting[random];
}

async function getMiddle(prompt)
{
    console.log("getMiddle('" + prompt + "')");
    
	const configuration = new Configuration({
		apiKey: "my-api-key-here",
	});
	const openai = new OpenAIApi(configuration);

	await openai.createCompletion({
			model: "text-davinci-003",
			prompt: prompt,
			temperature: 0.7,
			max_tokens: 500,
			top_p: 1,
			frequency_penalty: 0,
			presence_penalty: 0,
	}).then(res => {
        var text = res.data.choices[0].text;
        console.log('got response: ' + text);
        return text;
    }).catch(error => {
        console.log('Error: ' + error.message);
        return error.message;
    });
}

function getClosing(resp)
{
	return resp + '</sentence>';
}

The result of this is:

Event JSON

{
  "prompt": "what did the fox say?"
}

Response

{
  "statusCode": 200,
  "headers": {
    "Content-type": "application/json"
  },
  "body": "\"<sentence>Greetings undefined</sentence>\""
}

Function Logs

START RequestId: c7153471-1563-430d-889a-cb394737b5dd Version: $LATEST
2023-04-26T17:16:44.120Z	c7153471-1563-430d-889a-cb394737b5dd	INFO	getMiddle('what did the fox say?')
2023-04-26T17:16:46.119Z	c7153471-1563-430d-889a-cb394737b5dd	INFO	got response: 

The fox usually says, "Ring-ding-ding-ding-dingeringeding!"
2023-04-26T17:16:46.119Z	c7153471-1563-430d-889a-cb394737b5dd	INFO	getClosing("<sentence>Hi undefined")
2023-04-26T17:16:46.119Z	c7153471-1563-430d-889a-cb394737b5dd	INFO	output: <sentence>Hi undefined</sentence>
END RequestId: c7153471-1563-430d-889a-cb394737b5dd
REPORT RequestId: c7153471-1563-430d-889a-cb394737b5dd	Duration: 2039.43 ms	Billed Duration: 2040 ms	Memory Size: 128 MB	Max Memory Used: 77 MB