Do you think we should make this a helper function? I think there are several other places where we expect an address string set in the .env that might not be checksummed

We can make it a utility function; I only did it here because this was the only place I could see that we actually normalised addressed on input.

I'll update accordingly 👍

It may be easier to use a reviver in this case. JSON.parse's second parameter is an optional function that looks at keys/values. We could probably create a reviver function like:

/**
 * Converts a potential string/array of strings that match an address into a checksummed address
 **/
export function checksumAddress(value: unknown): unknown {
    const isArray = Array.isArray(value);
    const result: unknown[] = (isArray ? value : [value]).map((v) => utils.isAddress(v) ? utils.getAddress(v) : v;
    return isArray ? result : result[0];
}

JSON.parse(
    RELAYER_INVENTORY_CONFIG ?? {},
    (, v) => checksumAddress(v)
)