I Revived a 9-Year-Old App with OpenAI Codex with a Product Engineer Mindset

The author revived a nine-year-old app called Highlander, which had become broken due to outdated dependencies and deployment issues, by using OpenAI Codex with a "Product Engineer" mindset focused on fixing critical issues and shipping value quickly. Codex assisted with local revival, adding a demo login, security hardening, and deploying the app to Fly.io, including removing hardcoded localhost API calls to resolve mixed-content errors. The author plans to apply the same approach to revive a related React/Redux app, documenting the process to blend software engineering and product engineering skills for broader career opportunities.

Nine years ago, I built an app called Highlander. It was one of those projects you never forget, but over time it broke: old dependencies, outdated tooling, local setup drift, and deployment blockers. This week, I brought it back to life. Not by rewriting everything from scratch. By pairing with Codex and treating the work like a Product Engineer: fix what matters, unblock users, and ship value fast. The Problem: The app was frozen in time: It had been broken long enough that I honestly didn’t expect a quick recovery. The Approach: Product Engineering, Not Just Refactoring: I didn’t just “clean code.” I prioritized outcomes: That sequence mattered more than perfection. Product Development Context: This rebuild also reconnects to the original product planning work from the Highlander sprint board on Trello: Highlander product sprint board That board reflects early MVP scope, feature prioritization, and roadmap thinking. Revisiting the app now with Codex let me combine that original product intent with modern implementation and deployment practices. What Codex Helped Me Ship: 1 Local revival 2 Demo-ready UX. I added a demo login path directly in the UI. 3 Security hardening. Before deployment, I tightened core risks. 4 Deployment to Fly.io One of the most important production fixes was removing hardcoded localhost API calls That one change removed mixed-content/CORS issues on deployed pages. Why this matters for my career growth: I’m not making a hard transition away from software engineering. I’m intentionally blending Software Engineer + Product Engineer skills so I can widen my career options and be more valuable to a broader set of teams and employers. This project reflects that blend: It wasn’t just a code cleanup. It was an end-to-end product delivery exercise. What’s Next: I have another 9-year-old app: Highlander-react-redux. It uses the same backend API, but the frontend is React/Redux. Next, I’m going to use Codex again to revive it with the same Product Engineer lens: I’ll document that process too, including what worked, what failed, and what changed in my thinking. Highlander Project Demo: https://highlander.fly.dev/index.html Github: https://github.com/heriberto-codes/highlander