Lesson 4: Fix answers with a check, tune prompts with tests
26 min read·13 Oct 2026
Module 5 · Lesson 4 · About 55 minutes · Needs: Lesson 1 (the scaffold form, decide); Lesson 2 helps (a verifier); Module 4 Lesson 2 (dev and test splits)The situation
It is Thursday 2 July 2026, week 5. Grace Mwangi, billing admin of Hollis Bakery, writes in T-1027: "Please cancel and refund our annual plan, which renewed 9 days ago." The rule says refund_full: 2,400 USD, which Joel must approve.
Tomasz suggests: "Ask the model to check its own answer." Maya asks: "Could a program tune the prompt for us?" This lesson tests both and finds what each needs: a signal from outside the model. T-1027 is the running example.