Lesson 1: A design, in order, out loud

Module 15 · Lesson 1 · About 50 minutes · Needs: Module 3 (the estimator and docs/numbers.md), Module 4 lesson 2 (the ladder), Modules 5 to 13 for the paths and failures they settled. No model calls

The situation

Week 15, Monday 8 February 2027. Helen's design review is next Monday. Gareth books a 45-minute rehearsal and sets one rule: "Draw nothing until I have heard the problem and the numbers."

The running example is Joel's Q2 2027 target, the roadmap's worked estimate: 100,000 daily Ask users, 10 questions each, 2,000 tokens in, 500 out, 3 seconds. One sampled request carries the request path: trace ask-0446, a Tallis Retail Group employee on 18 September 2026, 1,986 tokens in, 374 out. Its twin on 22 September, ask-0646, carries the failures.