backend-observability

# Observability Instrumentation > The build-time counterpart to your monitoring stack. The Sentry plugin installs the SDK; `debug-sentry-monitor` triages after the fact; `audit-langfuse-llm` audits LLM traces. about instrumenting **correctly while you build** so those tools have signal to work with — and so a 3am incident is debuggable. ## When this fires Adding logging / tracing / metrics to new code, reviewing instrumentation, or fixing "we can't tell what happened in prod." Not for installing an SDK (use the Sentry/Langfuse plugins) or post-hoc triage (use the monitor/audit skills). ## The one rule that matters most: correlation A prod incident is only debuggable if you can pivot **error ↔ trace ↔ log ↔ user** from any one of them. Make every layer share an id. - Generate/propagate a **request id** (or OTel `trace_id`) at the entry point (HTTP middleware, edge function, job start). Put it in async context (`AsyncLocalStorage` / context var), not a parameter threaded everywhere. - **Stamp it on everything:** every log line, Sentry `setTag("request_id", id)` / `setContext`, and the Langfuse trace (`trace.id` or metadata). On an LLM error, attach the Langfuse trace URL to the Sentry event so you jump straight from the exception to the prompt/response. - Set user/session/tenant scope (`Sentry.setUser`, Langfuse `userId`/`sessionId`) — scrubbed (see redaction). ## Structured logging discipline - **Structured, not string-soup.** Emit JSON with stable fields (`level`, `msg`,...