Your question is Mock Activity-Tracking App Take-Home. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Implement a mock activity-tracking app with solid business logic and an improved, user-friendly UI: support start/stop recording with live metrics, persist sessions and show history, and add a post-launch gradual rollout using a feature-flag system that simulates backend control.