Live windev finding: after a client sent the ShutdownWorker control command
the worker exited 0 and WorkerClient moved to Closed on the shutdown ack,
but GatewaySession.State stayed Ready (even with an event stream attached)
until its lease expired.
IWorkerClient has no state-change callback, so the session observes the
worker from its own worker-event pump source: WorkerClient enters
Closed/Faulted before completing the event channel, so when the enumeration
ends ObserveWorkerTerminalState sees the terminal state and faults a Ready
session. Faulted rather than Closed: Closed means the gateway closed it and
would linger in the registry; a faulted session stays observable with the
reason and the faulted-session sweep reaps it, accounting SessionClosed
exactly once. Only a Ready session follows its worker, so a gateway-
initiated close is unaffected.
FakeWorkerHarness-based tests cover the ShutdownWorker exit and a broken
worker pipe.
Joseph Doherty