Phase 3: The Generate-Validate Loop · 90 min · Claude Code · Git · Python

Project: Spec'd & Validated Prototype

Orbit 1 ends here: one product, a real spec, a real context architecture, passing tests, a clean commit history, and a design doc someone else could actually review.

Hiring signal: This is the first of three portfolio-defining projects in this course — a working prototype with a spec, a validated context architecture, and a design doc is exactly what an interviewer means by 'show me something you built with AI, properly.'

What you will learn

Assemble a spec, a validated context architecture, passing tests, and a clean commit history into one working prototype milestone
Write a design doc that explains architecture decisions and alternatives considered, not just what was built
Distinguish a prototype that merely runs from one that is genuinely spec'd and validated
Run your course-long product through a consolidated Orbit 1 readiness gate before calling the milestone done

Introduction

Project: Spec'd & Validated Prototype

Two learners finish building the first version of their course-long product in the same week. The first has working code that runs, a folder of prompts they used along the way, and a sense that it's "basically done." The second has a spec with acceptance criteria written before any code existed, a context architecture that passed the health check from c12-02, a test suite where every test traces back to a specific acceptance criterion, a commit history where each commit is a validated checkpoint with a real message, and a one-to-two-page design doc explaining why they chose their architecture over the alternatives they considered. Both products might do the same thing when you run them. Only one of them is the deliverable this course means by "spec'd and validated prototype," and the difference is entirely in whether each of Orbit 1's disciplines actually got applied, not skipped in favor of just getting to something that runs.

This lesson doesn't teach a new technique. It's where the four preceding phases — the mindset shift, spec-driven development, context engineering, and the generate-validate loop — stop being separate lessons and become one milestone you actually ship.

What "done" means for this milestone

Your course-long product's first milestone is complete when four things are all true simultaneously, not when any one of them is: the working prototype satisfies every acceptance criterion from your c12-01 spec, verified by tests that were written from those criteria rather than from watching the code run; your context architecture from c12-02 passes its own health check (budget, rules-vs-skill, staleness, isolation); your commit history shows validated checkpoints with real, traceable messages, not one giant end-of-week commit; and you can produce a design doc that explains your architecture decisions to someone who wasn't in the room while you made them.

The gap between 'runs' and 'validated'
Code that runs on the inputs you happened to try is a demo. A validated prototype is one where you can point to a specific test for each acceptance criterion in your spec and show it passing — and where a stranger reading your design doc could ask 'why this approach and not X' and find the answer already written down, not discover you never considered X at all.

Unlock the full lesson

You've read the first 2 sections. The rest of this lesson covers Writing a design doc that's actually reviewable, Running the readiness gate before calling it done, Why this milestone, specifically, is worth defending, Build It — plus a hands-on lab, quiz, and project artifact.

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