One concrete answer from my own small tool: move the things you must stay in control of out of your head and into tests. Our privacy rules (drafts never stored

One concrete answer from my own small tool: move the things you must stay in control of out of your head and into tests. Our privacy rules (drafts never stored or logged) are executable, so any patch that quietly violates them fails the suite whether or not I reviewed that diff carefully that day. I still read the code, but the invariants no longer depend on my attention holding.