obs-metrics

The answer is in the metrics — latency percentiles, error ratios, saturation, rates, missing-data traps. Backends: Wavefront (WQL), Mimir/Prometheus (PromQL), and Cloud Monitoring on GCP (PromQL; MQL is deprecated). Triggers: 'query the metrics', 'graph the error rate', 'is latency up', 'write a metric alert query'. Not for alert design (obs-alerting) or logs (obs-logs). Deciding what a live page means or what to do next belongs to incident-investigation, which routes query work here.