observability

@colin4k1024

Set up and query Superagent's observability stack: OpenTelemetry traces, Prometheus metrics, and Grafana dashboards. TRIGGER when: debugging latency or errors via traces, adding custom metrics, configuring OTel collector, reading Grafana dashboards, or when the user asks "如何查看 trace", "metrics 怎么看", "observability 怎么接入", "add a span to my code". DO NOT TRIGGER when: working on agent logic, model routing, or frontend UI.