A coordinator agent fans out four research subagents, one per data source, and merges their findings into a report. In production, the report sometimes omits a whole section with no indication of why. Investigation shows that when a source API times out, the subagent catches the error and returns an empty string as its final message, which the coordinator treats as "nothing relevant found." The team wants the coordinator to retry transient failures, and to state clearly in the report which sources could not be covered. What is the best fix?