GPT-5.3-Codex vs GPT-5.6 Lunafor coding

The race is a classic **check-then-act** around an `await`.

### What goes wrong

`getConfig()` does:

1. Check `if (cache)`.
2. If empty, start `fetch` and `await`.

Because `await` yields control, another caller can run in between.

### Problematic interleaving

Assume two callers: A and B.

1. A calls `getConfig()`, sees `cache === null`.
2. A starts `fetch('/config')`, hits `await` (pauses).
3. B calls `getConfig()`, still sees `cache === null`.
4. B also starts `fetch('/config')`, hits `await`.

Now you have **two in-flight requests**.

If…

The race is caused by the `await` yielding control before `cache` is assigned.

For example:

1. Call A checks `cache` — it is `null`.
2. Call A starts `fetch()` and pauses at `await`.
3. Call B runs before A finishes and also checks `cache` — still `null`.
4. Call B starts a second `fetch()`.
5. Both requests eventually assign to `cache`; the one that finishes last determines the final value.

Thus, concurrent callers can cause duplicate requests and may even receive different results.

Cache the in-flight promise instead:

```js
let configPro…