The Evidence Locker Your Agent Doesn't Keep
Your trace logs every token. They log every tool call, every retry, every retrieval latency, every model id. They look exhaustive. Then a regulator, a customer, or your own incident channel asks the one question that should be easy: what did the model actually see at the moment it decided? And you discover that your trace recorded the questions but not the answers the model was looking at when it answered.
The retrieved chunks have rotated out of the vector store because the corpus was reindexed last Tuesday. The tool response was a streamed payload you stored only the final-state summary of, because storing the full stream tripled your bill. The system prompt was assembled at runtime from a feature flag that has since flipped twice, and your flag service does not retain historical values by timestamp. You have full observability over what happened — the call graph, the token counts, the latencies. You have nothing about what the model was answering against. That gap is the difference between a trace and a decision record, and most teams have not noticed they only built one of the two.
