Building an allocation system for en primeur
En primeur sells entitlement before stock exists. What an allocation system needs that a standard shopping cart does not have.
En primeur selling has a structural problem that most commerce software is not built to solve: you are selling wine that does not exist as physical stock yet, to a list of buyers who each have different entitlement based on history and relationship, under a release window that closes fast.
Generic ecommerce checkout assumes stock exists and anyone can buy it until it runs out. En primeur is closer to the opposite: entitlement exists before stock does, and the job of the system is to manage who gets access to how much, fairly and defensibly, not just to process a transaction. That is why allocation sits inside Commerce rather than beside it.
A functional allocation system needs a few things a standard storefront does not have.
Customer tiers that actually mean something. Not just a loyalty badge, but a real entitlement level that determines how many bottles or cases a given buyer can access at first release, based on purchase history or relationship.
A release mechanism, not just a product listing. Allocations typically open to a defined list at a defined time, with a window that closes, rather than staying open indefinitely like a normal catalog listing.
Fill tracking that shows what is actually happening in real time. How many offers went out, how many were confirmed, what the fill rate looks like by tier, so you can see whether a release is landing with the buyers it was meant to reach.
A path from allocation to fulfillment that does not require re-entering the same order into a different system, since the wine may not physically exist yet and could be delivered months later, sometimes into storage rather than shipped immediately.
Most commerce platforms treat this as an edge case to be handled manually with spreadsheets and email, because it does not fit the assumptions built into a standard shopping cart. For a business that runs en primeur as a real part of its calendar, that manual handling is not a minor inconvenience, it is a recurring, predictable cost every release cycle.