An enabled Find a Tender or mock source with no api_root used to start and then fail on every fetch. Its worker now returns an error naming the missing key before it starts, which stops Run. "fetch once" checks sources.find_a_tender.api_root the same way. TestRunMissingAPIRoot covers both sources, and TestRunLogsSourceErrors sets an api_root so it still tests the zero interval. The section docs and internal/config/README.md say what an empty api_root means.