System Design: AI Software Engineer (From Autocomplete to Autonomous App Builder)

Goal: Build a system that predicts the next line of code in 300ms, refactors 12 files in 45 seconds, and builds an entire app from a one-sentence spec over 4 hours.

1 million developers. 100 million completions per day. This is the blueprint.

How to read this: Three stories, three time scales.

Story one: a keystroke becomes ghost text in 300ms. Story two: "refactor auth to JWT" becomes a 12-file diff in 45 seconds.

Story three: "build me a SaaS app" becomes a deployed product in 4 hours. Each story goes deeper into the system.