We deployed a LangChain agent for a client and it silently failed for two weeks. Here's what we built to make sure it never happens again.

Six weeks ago, a LangChain agent we'd deployed for a B2B client started failing on roughly 30% of its sessions. No exceptions. No 500s. Nothing in the logs that looked wrong. The agent kept running, kept returning responses, kept looking completely healthy from the outside. We found out because the client called asking why their numbers looked off. Two weeks of silent failures. About $2,400 in wasted LLM spend before we even knew there was a problem. And the frustrating part wasn't that we…