nextConversationId

Generate a process-global, JVM-unique conversation id. Exposed for callers that want to construct messages with a pre-allocated id (rare). Note: contractNet does not use this — it draws from a per-model counter reset each replication, so its ids are reproducible run-to-run and isolated between models. If you mix manual ids with contractNet on the same mailboxes, pass a distinct prefix here to avoid any overlap with the default "cnp" namespace.