Phase 1: Spec-Driven Development · 45 min · Git · GitHub Actions · Python

Spec-Code Drift and How to Prevent It

Drift isn't a bug you fix later — it's invisible by construction until something blocks the merge that creates it.

What you will learn

Explain silent spec-code drift as a structural failure mode, not an occasional mistake
Describe how a drift gate makes spec-code divergence a blocking merge condition instead of an invisible one
Justify the same-commit contract update rule and why 'update the spec later' defeats the gate's purpose
Implement a real, git-based drift gate that detects business-logic changes made without a corresponding spec update

Introduction

Spec-Code Drift and How to Prevent It

Objective

Build a real drift gate that uses actual git diffs to detect when business-logic files changed without a corresponding spec update in the same commit, and blocks that commit.

Unlock the full lesson

You've read the first 2 sections. The rest of this lesson covers The Problem, The Concept, Build, Check Yourself, Key Terms & Next — plus a hands-on lab, quiz, and project artifact.

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