cubicweb #5245990 can't call a service in postcreate file [open]

sounds like they are not available in the registry at this point:

 File "/home/syt/src/clients/SAEM/cubicweb/server/session.py", line 1161, in call_service
   service = self.vreg['services'].select(regid, self, **kwargs)
 File "/usr/lib/python2.7/dist-packages/logilab/common/registry.py", line 566, in __getitem__
   raise exc
RegistryNotFound: services
prioritynormal
typebug
done in<not specified>
closed by<not specified>