Wrong HTTP status for timeout?

With a simple Dockerfile that always times out after 1s:

```Dockerfile
FROM public.ecr.aws/lambda/nodejs:12
RUN echo 'exports.handler = (_event, _context, cb) => { setTimeout(() => {}, 100000) }' > index.js
ENV AWS_LAMBDA_FUNCTION_TIMEOUT=1
CMD ["index.handler"]
```

Hitting the endpoint:

```
$ curl -qv http://localhost:8080/2015-03-31/functions/function/invocations -d '{}'
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> POST /2015-03-31/functions/function/invocations HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.64.1
> Accept: */*
> Content-Length: 2
> Content-Type: application/x-www-form-urlencoded
>
* upload completely sent off: 2 out of 2 bytes
< HTTP/1.1 200 OK
< Date: Tue, 19 Jan 2021 02:38:17 GMT
< Content-Length: 33
< Content-Type: text/plain; charset=utf-8
<
* Connection #0 to host localhost left intact
Task timed out after 1.00 seconds* Closing connection 0
```

Returns status code 200 and no special response headers.

I didn't find conclusive documentation on what exactly should happen, but the [screenshot](https://theburningmonk.com/wp-content/uploads/2019/05/img_5ce5e801baffb.png) on [this page](https://theburningmonk.com/2019/05/how-to-log-timed-out-lambda-invocations/) seems to suggest that a "real" lambda would return 502.

Reproduce the timeout using the provided Dockerfile and POST to the documented invocation endpoint with curl. Compare the emulator’s 200 response and headers with the real Lambda behavior described in the linked article, then establish the expected status and headers; done means timeout responses match that behavior.

Written by the indexing model from the issue text.