Expansion through the published inference package.
Completion returns the neutral response, including object, usage, cost and
trace. Streaming consumes neutral events, calls an optional on_event observer
and a monitor callback (:halt rejects generation), and retains the final
response when supplied by the provider. A monitor may use TypeSafe contracts.
Physical cancellation is provider-dependent: a Pristine token is forwarded in
request options only when the client explicitly declares :cancellation as
supported. Other clients have local cancellation only. Require that capability
at run startup when physical cancellation is essential.