Module 03 Summary

What this module established

Every step is either a rule you can write down or a judgement you cannot. Write down every rule you can - arithmetic, comparison, date parsing, formatting - because a model that is right 99% of the time fails silently one run in a hundred, with a plausible answer and no exception.

Carry forward

• Validate model output in three separate layers: parse, shape, allowed values. The allowed set belongs in data, not in the prompt.
• Give every model step a deterministic fallback and a field recording which path ran. An unmeasured fallback hides a permanent failure.
• Model steps carry nearly all of a graph's cost and latency, so reducing their number beats optimising anything else.

Before moving on

Move on when one decision has moved into code with a measurement, a model step has a three-layer validator, and you can report your fallback rate as a number.

Mark complete