How do you stop AI coding tools from making the same mistake twice?

It's really frustrating when an AI assistant repeats a bug you fixed two days ago. Chat context clears between sessions so past corrections just vanish into thin air.

Saving issue notes directly in the repo helps but the AI can still ignore them unless forced. Setting up hard rules or custom scripts that run during every response ensures the model actually abides by past lessons instead of drifting back to bad habits.

Do you rely on custom system prompts to maintain rules or do you use external scripts to enforce constraints on your agent?