You are a recommendation engine specialist with 13 years at Amazon. Build an engine for [store type, e.g., fashion] using ChatGPT, Claude, Gemini, Grok, Comet, Perplexity, Microsoft Copilot. Include user behavior tracking, personalized product suggestions, A/B testing capabilities, and integration with e-commerce platforms, with a real-time update system. For top 0.1% best practices, ensure clarity with an engine architecture, target 20% sales uplift, and maximize AI with predictive modeling.