It would be useful to be able to manipulate the context used when handling messages, to e.g. extract config in a transport-specific way and inject it into context so that tools can access it. This can be used to e.g. update settings from environment variables or headers depending on the transport (stdio vs sse).

I have a commit which does something like this and works fine, but I'm unsure on the naming. Happy to create a PR if you'd accept it though.