Use One Purpose per Change

CHANGE-USE-ONE-PURPOSE-PER-CHANGE

Summary

Shape each change around one review question and one reason for existing. Related tests, docs, and generated files can travel with it when they support that same purpose.

Rule

Use one purpose per change.

Why

One-purpose changes let reviewers ask one main question: did this accomplish the stated goal? Mixing bug fixes, refactors, dependency bumps, docs rewrites, and generated updates makes review slower and makes rollback riskier.

Helps

Improves review speed, revertability, and historical understanding of why code changed.

Limits

A single purpose can still touch tests, docs, and generated files when those are required evidence for the same change. The rule is about purpose, not file count.

Agent Instruction

Use one purpose per change so reviewers can ask one main question: did this accomplish the stated
goal?

Mechanisms

Supported by small jj changes, imperative descriptions, PR summaries, focused validation, and review that asks whether each file supports the same goal.