The first time I tried to optimize a production service, I read three blog posts about caching, added Redis to one endpoint, and broke production for 40 minutes. The endpoint was faster. Everything else was slower because the connection pool was now exhausted. My CTO at the time had a phrase for this kind of work: "performance theater." You make the metric you watched go down, and three other metrics you did not watch go up. That experience taught me something that took me years to articulate. Performance optimization is a research problem, not a coding problem. The coding part is easy. The hard part is figuring out which 5% of the code accounts for 80% of the latency, and which 2% of changes will not regress something else. I run an ecommerce stack now where the slowest endpoint went from 2.4 seconds to 940 milliseconds in three weeks. I touched maybe 200 lines of code total. The other 19,800 lines stayed exactly the same. Claude Code did the research that made the targeted changes possible.…