You deploy an AI agent. It runs for six hours. Then it crashes. A memory leak, a stale API token, a full disk — something always breaks. You restart it, and the cycle repeats. After running an autonomous AI system through 7,400+ continuous cycles over three months, I've learned that the hardest engineering problem isn't building the agent — it's keeping it alive. This article describes the watchdog pattern: a layered self-repair architecture that lets AI systems detect, diagnose, and recover from failures without human intervention. The Core Problem Long-running AI agents face a class of failures that don't exist in traditional software: Context death : The agent's working memory fills up and it loses track of what it was doing Cascade failure : One broken service (email, database, API) creates a chain reaction Drift : The agent gradually diverges from its intended behavior over hundreds of cycles Silent failure : The agent appears healthy but stopped doing useful work Traditional monitoring catches crashes.…