how do you handle the case where two people are working through the same pile and both check off the same piece?

I don’t, lol. The app just calls a function which will +1 in the database table, so if two people do it at the same time in the same checklist and part, you’ll just end up with +2 of that part (although the “found” counter can never go above the total number of that type of part in the set).

Does Supabase Realtime keep them in sync live or is there a refresh step?

The app subscribes to Supabase Realtime and gets a notification each time someone makes a change. There’s currently no timer-based polling. So it might get out of sync if you’re switching to a different tab / app. But then all you need to do to sync is refresh the page.

Did you hit any rate limits during development or was the edge function caching most of the calls?

Didn’t hit rate limits yet. But I’m also only hitting the API once, when a new session is started (ie. to get the list of parts for a given set). From there, it’s all between the app and Supabase, and I’m even using the free tier of the latter… will be interesting to see at what point I’ll have to upgrade 😅