TL;DR Many LLM observability setups capture prompts, outputs, tokens, and latency while leaving retrieval failures hidden. A single search call may conceal query rewriting, filtering, fetching, deduplication, reranking, and evidence selection. A useful trace connects the original question to the effective query, returned sources, selected passages, and final claims. Retrieval tracing helps distinguish missing, stale, or ignored evidence from a genuine generation failure. Production...