When federated nodes are created (via external projections), it is critical that there is a valid Federated Node Id -> External Projection Id mapping, so that a correct parent back-reference can be created.

Currently those mappings are transient, held only in memory by the FederatedDocumentStore. In addition to the current behavior, we should make sure these mappings are stored (probably in the system area) when the repository shuts down and re-loaded when it starts up.