Last month, a production agent at a startup started hallucinating customer data. Every API call returned 200 OK. The agent's dashboard showed green across the board. Latency was normal. Error rate was zero. Six hours later, the billing arrived: $2,847 in tokens for a single user query that entered a reasoning loop and never stopped. This isn't a hypothetical. The Operator Collective documented $47,000 runaway agent invoices in 2025. In 2026, the numbers are only going up as agents get more autonomous and cheaper per token. The problem is fundamental: traditional monitoring was built for deterministic software. Request comes in, code executes, response goes out. Same input always produces same output. You know what "healthy" looks like. AI agents break that contract. The same prompt can spiral through 15 reasoning iterations, call 40 tools, and produce a confident but completely wrong answer — all returning HTTP 200. Your dashboards stay green. Your agent is on fire.…