Glovida

Regulated retail imposes constraints that ordinary commerce does not: caps on quantities of particular products, restrictions on what can be bought together, and eligibility that depends on the customer rather than the catalogue. A client-side check on the cart page satisfies none of these — the cart is mutable from the API, and checkout is reachable directly.

Validation lives in a Shopify Function running server-side inside the platform's own cart and checkout evaluation, with a companion checkout extension surfacing the reason clearly to the customer. The browser gets a fast, friendly version of the same rules for immediate feedback; the browser is not what is trusted.

That split — advisory in the client, authoritative on the server — is the entire design. The client-side copy exists purely so the customer finds out at the point of adding rather than at the point of paying.

A companion Shopify admin app for the operations side, plus the cart-validation extension package. The storefront work also carried a staging clone used to trial theme changes against production data before release, which is the kind of unglamorous infrastructure that stops a pharmacy storefront breaking on a Friday.