Claude Code hooks: why "just tell it not to" doesn't hold up

If you've spent time customizing Claude Code, you've probably written a line like this in your CLAUDE.md : "always run the formatter after editing a file" or "never touch .env or any .pem / .key file." It works — until a long session, a big diff, or a context window full of other instructions makes that one line easy to deprioritize. The model isn't being careless; a system prompt is advisory. Every instruction in it competes with everything else in context for attention, and instructions…