Every ecommerce developer knows the metrics their clients obsess over. Revenue. Conversion rate. CAC. ROAS. Chargeback rate. Almost none of them track sync lag. Sync lag is the gap between when a sale happens on one channel and when every other connected channel finds out about it. It sounds like an infrastructure detail. The business impact is anything but. Here's why sync lag is the most expensive metric nobody measures and the architectural decision that eliminates it. What sync lag actually costs Lost sales that leave no trace An AI agent shopping on behalf of a consumer queries your inventory at minute 14 of a 15-minute sync cycle. It sees stock that sold 13 minutes ago. It flags the product as unavailable. It moves to a competitor. No abandoned cart event fires. No bounce rate spike. No notification of any kind. Just a sale that never happened invisible in every analytics dashboard the client is looking at. Marketplace ranking damage that looks unrelated Every oversell produces a cancellation.…