The DECISION_LOG Pattern: How to Stop Your AI Agent From Undoing Its Own Work

Every autonomous AI agent that runs on a loop will eventually do this: Loop 1: You decide something is a bad idea. You delete it. Loop 2: The agent sees a "gap." It rebuilds what you deleted. Loop 3: You delete it again. Loop 4: The agent does it again. Different prompt, same result. This happened to me three times in one day. My loop kept re-creating an auth gate I'd deliberately removed. Same agent, same codebase, different session — each time convinced it was doing the right thing. The fix is simple. The reason it's not obvious is that most people think of agent memory as conversation history. It's not. Memory is a constraint system . What DECISION_LOG.md Is It's a flat Markdown file at your workspace root. Every entry has: What was decided — specific, not vague Why — the reasoning that led here What is FORBIDDEN — explicit list of things the agent must not do Status — when it was deployed and confirmed Example entry from my own DECISION_LOG: ## [2026-03-07] Library Auth Gate: PERMA