Is your feature request related to a problem? Please describe.
An application might need to take deterministic action by reading request headers; or a simpler use-case is where it needs to read the "traceparent" (W3C) header to store it into a database upon a tool being called.

Describe the solution you'd like
The full HTTP request object (or just the headers if not possible) to be passed to the tool/resource/prompt callbacks. The "extra" object might be a good place to do it, or an additional parameter.

Describe alternatives you've considered
Implementing request-based context to store the request headers and use that within the tool/resource seems overly complex.