For decades, software engineering followed an unwritten golden rule: "Never rewrite legacy systems from scratch."

Refactoring in place was almost always the safer, more conservative path. Rewrites were notorious for cost overruns, missed deadlines, and lost business logic hidden deep within millions of lines of C/C++ code.

However, the rise of agentic AI coding assistants and modern code-generation pipelines is flipping this classic playbook on its head.

The Modern Dilemma: AI-Accelerated Velocity vs. Structural Decay

AI models can now generate entire modules, write unit tests, and translate legacy paradigms into modern C++ syntax in a fraction of the time it takes human teams. This makes greenfield rewrites look far more enticing than ever before.

But there is a catch.

AI tools optimize for local correctness —getting a specific function or class to compile and pass local unit tests.…