You are evaluating an aging core service that still powers an important part of a B2B SaaS platform. The system has accumulated technical debt, delivery speed is slowing, and reliability issues are starting to affect adjacent teams, but it also contains years of business logic that would be expensive to rediscover. You need to decide whether to refactor incrementally, rewrite the system, or continue investing in the current architecture for now.
How do you decide whether to refactor, rewrite, or keep investing in an existing system?