The Checkpoint Pattern: Save and Resume Long AI Coding Sessions

You’re three hours into an AI-assisted refactoring session. The context window is stuffed. You ask for “one more change” and the model hallucinates a function that doesn’t exist. Sound familiar? The problem isn’t the model — it’s that you never saved your progress. The Pattern A checkpoint is a small markdown file you write (or ask your assistant to write) at natural pause points during a long session. It captures: What’s done — files changed, tests passing What’s next — the immediate next task Key decisions — why you chose approach A over B Active constraints — things the model must not touch Here’s the template: # Checkpoint: Auth Refactor — Step 3 of 5 ## Completed - Extracted `AuthService` from `UserController` - Added unit tests for token refresh flow - Migrated 3/7 endpoints to new service ## Next - Migrate `/api/users/me` endpoint - Update integration tests ## Decisions - Chose refresh-token rotation over sliding expiry (see PR #142 discussion) - Keeping legacy `authenticate()`