A multi-agent analysis system produced a wrong final answer. Each agent writes its own logs with its own request IDs, and the team cannot determine which handoff introduced the error. What is the best first investment?

Answer: A — Propagate one trace ID through every delegation and tool call, logging each handoff's inputs and outputs

Root-causing errors across agents requires connecting the hops; (a) makes each handoff traceable. (b) may catch some errors but does not explain where they arise. (c) adds volume without correlation. (d) guesses at a fix without diagnosis.