A CLAUDE.md-style instructions file
Rather than re-explaining project conventions every session — which package manager to use, which directories are off-limits, which patterns the codebase prefers — you can write them once into a project-level instructions file that the agent reads automatically at the start of a session. This turns tribal knowledge that used to live only in a senior engineer's head, or that got repeated in every single prompt, into something durable and shared: any session, run by anyone on the team, starts with the same baseline understanding of how this particular codebase wants to be worked on.
The most useful entries are the ones that aren't obvious from reading the code itself: "run tests with pnpm test, not npm test," "never edit files under generated/," "use our Result<T, E> type instead of throwing exceptions." A rule the agent could already infer from the codebase (like an obvious naming convention visible everywhere) adds less value than a rule capturing a decision or constraint that lives only in the team's collective memory.