Objects (when used as they were intended and not the way some people tend to use them) should have a logical grouping of attributes and responsibilities. Ideally each object should be composable and have a singe responsibility but when that's not plausible or sensible each object should be the grouping of logically related items.

A `PreparedRequest` should only pertain to the actual request - the headers, the method, the body, the requested URL, etc. What is not logically related to a `PreparedRequest` is information that pertains to how the Adapter sends that request. That's why these should never be stored on `PreparedRequest` objects. They're logically (and semantically) not related and so they do not belong.