Series · 3 parts
Migrating with AI
I inherited the company's most complex system without knowing its domain. Finishing on time by hand was out of the question, so I brought in AI — and the migration is done. These three posts cover the first month burned for lack of direction, the verification harness built one mistake at a time until it caught a major error before launch, and the day I rolled back a week of working AI code myself.
- I Inherited the Company's Most Complex System, and I Didn't Know the Domain
When the migration lead left, the company's most complex system landed whole on me, two years and three months in. A domain I'd never touched, and a first four weeks spent leaning on AI. Only then did I change direction.
- How I Kept AI From Breaking Production
While inspecting pre-launch data, a check I'd stood up in code caught a purchase-cost error worth billions of won. After the four weeks I burned in Part 1, the story of the fences and recorders I bolted on to hold the AI in place — up to the moment it first earned its keep.
- AI Built a Week's Work, and I Rolled It Back
I gave Codex a single goal and left it a few days; I came back to a week's worth of code stacked across a dozen-odd tables. It ran fine, but it was more than I could review. The story of finishing a production migration with two AIs running side by side — and the one time I had to stop it.