Thinking Fast & Slow for a Personalized Notification System

What this post added

Introduced a hierarchical 'Slow-Fast' architecture for the personalized notification system. The 'Slow' policy makes strategic decisions about a member's weekly messaging plan (frequency and pacing) by maximizing a utility function that balances engagement signals against long-term messaging costs. The 'Fast' policy executes tactical send decisions based on this plan, pulling it from a low-latency feature store. This decouples frequency planning from message selection, enabling independent evolution of both components and improving member experience by respecting longer-term horizons.