I'd been incorrectly using indirection against Cython's build_ext
module.

On the service-side, an operation isn't successfully completed with
just the conclusion of transmission to the other side; local ingestion
of the status and code must be completed as well before termination
callbacks are called.

This exposes a bug somewhere in how channel connectivity events get
published on completion queues. Investigation remains active.

These changes should have been included in dc8c3239.