observability

Discipline for making a service's health answerable without reading its code, structured logging, the four golden signals (latency, errors, traffic, saturation), and an SLI/SLO/error-budget definition with alerts that link a runbook. Use when adding logging to a service, instrumenting metrics or tracing, defining what "healthy" means for a service, setting up alerts, or when the user asks how to monitor, debug in…