Ask HN: How to successfully manage a long-term codebase?

My company's codebase is completing seven years since its first line was written. I know it's not that old, but as I talk with fellow developers from other companies I can spot a few differences as a result of how each codebase has been managed that directly affect team productivity, engagement and happiness: - Perception of architectural consistency - Perception of quality and robustness - Willingness to adopt "new trends" - Amount of technical debt - Frequency of partial/total rewrites - Operational complexity and costs About a year ago I posted a few learnings from my own experience managing our codebase since its inception: - https://thomasvilhena.com/2019/11/system-design-coherence So I'm interested in your experience and learnings managing a long-term code base, both what your team did right and what went wrong. Thanks in advance!