Slash command
A word starting with / that you type to make the harness do something right now: clear the context, switch mode, or run a saved prompt. You type it, not the agent.
It turns a long instruction you repeat into one word, so the careful version becomes the easy version. If you type the same review prompt every day, it should be a command the whole team shares.
Say it to your agent
“Make a /review-diff command in .claude/commands/review-diff.md. It runs git diff main, and for each changed file says what could break, with the line number. Commit it so the team gets it.”