Book Events — the tightest constraint holds the gate.

Every event ticketing app counts seats. Almost no real venue is limited by seats. A farm dinner is limited by seats and kitchen staff; a pottery studio by wheels and kilns; a goat yoga class, genuinely, by goats. Sell a family of five into a room that has the chairs but not the second cook, and the merchant finds out on the night.

Book Events models capacity as resource pools. A booking draws weighted amounts from several at once and the tightest one binds — and when it binds, the shopper is told which constraint stopped them, in the merchant’s own words, rather than watching a button fail.

It is an embedded Shopify app, which means the interesting problems are boundary problems. Money only moves through the merchant’s own checkout, so events have to become products and ticket types variants and stay in sync. The theme’s own Buy-it-now button is a second front door that skips the date, the attendee details and the capacity hold — so it isn’t hidden, it’s refused by a checkout validation function, because a control you can only see in the UI is not a control.

This is the product where the operating model shows up most plainly as documents. Eleven architecture decision records, each naming the Jira issues it constrains and the vendor documentation it was checked against, with the date. Written for a reader who will be an AI as often as a person — and a decision whose blast radius isn’t on the record gets relitigated every single time.