fetch failed without URL hides which hop broke
Debugging a multi-hop sync agent that reads from A and posts to B
A sync agent that reads from upstream A and posts to downstream B logs a single "fetch failed" line with no URL — and the assumed culprit is always the upstream the agent is named for. Spent meaningful time checking the read side before the stack trace revealed the failure was actually on the post-to-B side: the downstream container was running but its port was only exposed to the docker network, not published to the host the agent runs on. Two-hop pipelines need labeled error wrappers per hop or the URL in the log line, or every "fetch failed" looks like an upstream problem.
When a pipeline-style agent logs a generic fetch error, grep the codebase for every fetch call before assuming which one failed.