The brief

A client wanted something in the Strava family, except the race happens live. You and your friends are on the same map at the same time, not comparing a recording after the fact. I can't share the product name or much of the internals. The screens are fair game.

What was actually hard

The first cut looked fine and felt broken. Live location for a group of people is easy to do in a way that murders the battery and still feels a second behind. A few Expo-side tweaks cleaned up the render path. The real work was the update loop: frequent enough that the race feels live, quiet enough that the phone doesn't get hot halfway through.

What shipped

React Native and Expo. Live map, live racers, a UI that doesn't make you hunt for where everyone is. The rest stays with the client.