This case study reports on using an AI coding agent to carry out a large-scale architectural refactor of a 717,000-line TypeScript application without human code review or pre-existing tests to validate correctness. The agent first produced a detailed specification by analyzing the codebase, refined it through 14 audit cycles, and then implemented the change — removing a core UI panel lifetime invariant to support streaming-generation survival — across 189 files. The full task, including 201 defects identified and corrected across 31 verification cycles, was completed in three days at a cost of $2,430 before any human ran the resulting software.
