Vigiles
Sometimes it helps to be able to examine, in totality, the request your Rails application received, and the specific response it elicited. Very handy when you're debugging. Also very handy when your engineers have to assist non-technical customer support staff. That aside, it's generally a great visualization of the black box abstraction, where your entire application is seen as one logical function, taking input (request) and producing output (response).
At the moment, this gem is unable to conduct you on your research journey from a given request to its response: you'd have to call on your logs and other observability systems you've engaged. But it's easy—rather, possible—to see how we can bring this in house, with a little tracing.