
This essay argues that AI is reshaping software at an architectural level — moving from human-centered applications to a composable agentic ecosystem where CLIs, Skills, and MCP form distinct layers that agents invoke as primary users.

Why did developers abandon polished IDEs for a terminal tool? The answer is less about AI than about Unix—a 50-year-old design philosophy of composable text tools that proves to be the perfect substrate for machine intelligence, and a preview of the AUI paradigm ahead.