1. A method performed on a computing device, the method comprising: rejecting, in response to a conversation continuation not existing on a system and a non-conversation continuation or a governing continuation existing on the system, a request to resume the conversation continuation, where the conversation continuation is configured for resuming an activity in response to a message from an external service that is engaged in a conversation with the activity, where the non-conversation continuation is configured for resuming the activity in response to a message indicating completion of an operation associated with the activity, where the governing continuation is configured for controlling continued execution of dependent continuations, and where the conversation continuation and the non-conversation continuation are included in a continuation list; delaying, in response to the conversation continuation not existing on the system and no non-conversation continuations or governing continuations existing on the system, handling of the request to resume the conversation continuation; and accepting, in response to the conversation continuation existing on the system, the request to resume the conversation continuation.