OpenStrap/edge ? reverse-engineered prompt

Build me a Flutter app for iPhone and Android that can connect to a WHOOP 4.0 band over Bluetooth and keep working without any WHOOP subscription.

I want it to pair with the band, pull the health and workout data onto the phone, calculate the main stats locally, and show simple screens for today, sleep, heart, stress, breathing, body, steps, workouts, records, recap, and profile. It should also support background syncing so the band keeps updating even when I am not opening the app all the time.

Please make it save data on device first, with no cloud dependency, and let me export my data if I want to. If it makes sense, include Apple Health and Google Health Connect sync for the raw measurements, plus a widget and a few helpful shortcuts on iPhone. I know the numbers will be based on public research and won’t match the official app exactly, so keep it honest and clear in the UI. If you need to look up current docs online, go ahead.