The agent queries metrics during a known outage window and reports everything looks healthy — no error, just empty series. Why?
The silent failure of observability agents: time-range defaulting plus datasource UID mismatch. Query tools default to a recent window (typically the last hour); if the incident was three hours ago, the response is a valid, empty result set — and the agent, trained to please, reports system nominal. The second variant is worse: datasource references are opaque UIDs per Grafana instance, and a wrong UID returns no data, never an unknown datasource error. The engineering fix: make explicit time ranges a non-negotiable prompting rule anchored to the alert timestamp, and verify datasource UIDs with a list-datasources call at session start. Empty metrics are a query bug until proven otherwise — never let the agent interpret them as health.