Observability

Status: Accepted (2026-09-14), amended by ADR-0019 (SDK in its own module) and ADR-0028 (Grafana opt-in)

Context: Telemetry must be on by default without vendor lock-in or cognitive load.

Options: Vendor SDKs; Prometheus + Zap; slog + OpenTelemetry.

Decision: slog for logs (stdout), OTel for traces/metrics configured via standard OTEL_* env vars; OTLP logs opt-in until the Go logs signal is stable; /livez, /readyz.

Why: Standards with the widest backend support; logs still work with zero infrastructure.

Tradeoffs: OTel SDK adds dependency weight and some startup cost.

Consequences: All modules instrument via OTel APIs and accept *slog.Logger; no module may depend on a vendor telemetry SDK.