The find-non-progressing-operation op isn't marked as read-only or runtime-only (it's both) so it isn't accessible to external callers on a domain server.
The related cancel-non-progressing-operation is marked runtime-only, so it's accessible. There's no point allow cancellation (which changes things) and not allowing a find (which just reads), so we should make the find visible.
A requirement of fixing this though is there need to be new test methods added to OperationCancellationTest case that test finding and cancelling the op via the server resource and not just via the host. The existing testFindNonProgressingOperation() can just have a second "find" op added after the current one, and then new variants of testCancellingNonProgressingDomainRollout() and testFindNonProgressingDomainRollout() can be added that use the full server address for the find/cancel op.