Currently, every Client may have a Session (here). I think we should formalize this relationship:

• We should invariant that every ingress Client has a Session and every service Client does not.
• We should have a Client pointer in Session that is valid only if the Session is an ingress Session.

This will make it easier to work with ingress Client instances and allow us to access decorations deeper into the transport infrastructure.

Acceptance criteria:

The relationship between client and session objects is clear and hard to misuse and properly encoded in the type system.