AI is transforming how apps are built, but not what they're built on. Without a cross-platform framework, agents must generate, verify, and maintain separate code for every platform, or degrade to web pages that don't feel native. This talk draws on lessons from evolving Lynx, the cross-platform framework behind TikTok and CapCut, to present three design principles for making app infrastructure AI-native: AI-Ergonomic (harness-able), AI-Efficient (token-economical), and AI-Expressive (intent-driven UI).