> I can't read the source code since it's 8 million lines of code and written in a programming language I don't know and in a language I don't speak.

^ This is the real world. Some comments talked about how maintainability is king and you just can't keep a mental model together of what the LLM produced. In real life software there is no single person with a mental model of how the system works end to end. In the most ideal scenario you have an architecture diagram, some readme's, and a runbook of how to use the system or get it running in a dev environment. Everything else is manually tracing through mountains of code of wildly varying quality.

coding harnesses are god sent tools when it comes to analysis and maintainability of existing code bases (including code they have produced).