Observability tools: Langfuse vs Phoenix vs W&B Weave

Review from deployments: - Langfuse: Excellent tracing, prompt/version analytics, user feedback capture. Quick to add. - Phoenix (Arize): Strong evaluation workflows and dataset-centric debugging; great for RAG diagnostics. - W&B Weave: End-to-end experiment lineage; strong for teams already on W&B. Advice: Pick one primary and integrate signals into your data warehouse. Alert on regressions of core metrics (faithfulness, latency, cost).