What A Twelve-Day Codex Session Revealed About Persistent Engineering Agents

Thu, 28 May 2026 00:00:00 +0000

The REX frozen-failure cleanup was a compiler project, but it was also an agent project.

For twelve days, Codex worked through a large historical CTest failure set in a real codebase. The task was not a toy benchmark. It involved a Clang frontend, a source-to-source AST, an unparser, token and source-position preservation, OpenMP and Fortran guardrails, midend analyses, generated files, reference outputs, review comments, hooks, and full-suite CTest runs.

That is the kind of task where many agent demos stop being useful.

Engineering on ./Code

What A Twelve-Day Codex Session Revealed About Persistent Engineering Agents