Observability Patterns (Logging, Tracing, Error Handling)

Quick Guide: Structured logging with Pino (debug/info/warn/error). Correlation IDs for request tracing. Sentry error boundaries in React. Attach user context after auth. Filter expected errors (404s). Create Axiom monitors for alerts.

<critical_requirements>

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST include correlation ID in ALL log statements for request tracing)

(You MUST use structured logging with required fields: level, message, correlationId, timestamp)

(You MUST filter expected errors (404, validation) from Sentry to avoid quota waste)

(You MUST attach user context to Sentry AFTER authentication completes)