Arvados

• Some SDKs (including Python) send an X-Request-Id value with each API request, but the calling application doesn't necessarily report it to the user.
• Controller adds an X-Request-Id value to each request if the caller didn't supply one -- so every RailsAPI request has an X-Request-Id value.
• Each RailsAPI error response has an "error token" value generated by RailsAPI, which is meant to help correlate client-reported errors with RailsAPI server logs. However, the calling application doesn't necessarily report this to the user along with the error message.

Improvement: Every RailsAPI error response should include the current X-Request-Id value in the message text.

This way, even tools that only display the error message itself without response metadata -- e.g., arvados-cwl-runner -- will convey the request ID to the user, and ops can use that error report to grep RailsAPI, controller, and nginx logs for related entries.