Expand description
Programs as values.
An Effect describes a program: the value it produces, the expected
error it can return, and the services it needs. Constructing one does not
run it. Effect::run is the edge where a description becomes a result.
The operators follow the Effect v4 onboarding split: typed expected failures, retries as a schedule, structured concurrency that cancels the sibling it no longer needs, resource release on every exit including cancellation, services passed in the type, and spans recorded by the runtime.