Our shop previously used the Fulfillment API to automatically fulfill open orders for a specific product every night. The product is digital and is fulfilled via email by an automated process. We run a cleanup script every night to identify paid / unfulfilled orders for this product and then mark them as fulfilled.
I have reviewed a bunch of the new Fulfillment Orders documentation and it all feels like overkill for this use case. Can someone point me in the right direction? We aren't really looking to be a fulfillment app or an order management app, would just like to fulfill orders of a specific product ID in an automated fashion.
Your script can now check for fulfillment orders containing the product with this ID and create fulfillments for these fulfillment orders. The only difference will be that you query for fulfillment orders rather than for orders. Fulfilling orders now is only possible through examining fulfillment orders. It's made for grater customization and allows multiple fulfillment scenarios to work together on the same customer order. In your case, I assume you can skip queuing orders.
Regarding examples from documentation, it's an order management app example, just very simplified.