first commit

packages/dev-server/src/realtime-bus.ts

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+/**
+ * Build the cross-process realtime bus from config. When realtime scaling is
+ * enabled, room broadcasts are bridged over Redis pub/sub so they reach clients
+ * on every app process/instance (multiple runs, or multiple apps behind the
+ * gateway). Returns undefined when scaling is off (single-process realtime).
+ */
+
+import type { RealtimeBus } from "@wrnexus/core";
+import { createPubSub } from "@wrnexus/pubsub";
+import { redisDriver } from "@wrnexus/pubsub/redis";
+
+export function realtimeBusFromConfig(cfg?: {
+  scale?: boolean;
+  redisUrl?: string;
+}): RealtimeBus | undefined {
+  if (!cfg?.scale && !cfg?.redisUrl) return undefined;
+  return createPubSub(redisDriver(cfg.redisUrl));
+}