1. A method of processing a client-initiated request, performed by a respective server system having one or more processors and memory storing one or more programs that when executed by the one or more processors cause the respective server system to perform the method, the method comprising: receiving, from a client system, the client-initiated request; after receiving the client-initiated request, determining whether at least a first predefined number of other server systems have a predefined task-processing status for the client-initiated request indicating that the other server systems have undertaken performance of a corresponding task-processing operation for the request; in accordance with a determination that less than the first predefined number of other server systems in the set of other server systems have the predefined task-processing status for the client-initiated request: sending a processing-status message to one or more of the server systems in the set of other server systems indicating that the respective server system has undertaken performance of the corresponding task-processing operation for the request; performing the corresponding task-processing operation; and upon completing the task-processing of the request, sending a result of the processing to the client system contingent upon a status of the other server systems in the set of other server systems.