Ctx defines the Context type, which carries deadlines, cancelation futures, and other request-scoped values accross API boundaries and between processes.
It is similar to Go's context package. The main use case is to have incoming requests to a server create a Context. This Context is propagated in the chain of function calls between the incoming request until the outging response. On its way, the Context can be replaced with a derived Context using with_cancel, with_deadline, with_timeout, or with_value.