Add LastOwnerKeyId capture to FakeSessionManager and assert it equals
"operator01" in OpenSession_WithValidRequest_ReturnsSessionDetails, closing
the gap where OwnerKeyId threading through the service layer had no test
coverage. Add a <remarks> to the 11-param GatewaySession convenience ctor
documenting that OwnerKeyId is null there and authenticated call sites must
use the 12-param overload.
Joseph Doherty
a43b2ee6af