relay: add control channel and heartbeat stream

src/infra/heartbeat-events.ts

@@ -0,0 +1,35 @@
+export type HeartbeatEventPayload = {
+  ts: number;
+  status: "sent" | "ok-empty" | "ok-token" | "skipped" | "failed";
+  to?: string;
+  preview?: string;
+  durationMs?: number;
+  hasMedia?: boolean;
+  reason?: string;
+};
+
+let lastHeartbeat: HeartbeatEventPayload | null = null;
+const listeners = new Set<(evt: HeartbeatEventPayload) => void>();
+
+export function emitHeartbeatEvent(evt: Omit<HeartbeatEventPayload, "ts">) {
+  const enriched: HeartbeatEventPayload = { ts: Date.now(), ...evt };
+  lastHeartbeat = enriched;
+  for (const listener of listeners) {
+    try {
+      listener(enriched);
+    } catch {
+      /* ignore */
+    }
+  }
+}
+
+export function onHeartbeatEvent(
+  listener: (evt: HeartbeatEventPayload) => void,
+): () => void {
+  listeners.add(listener);
+  return () => listeners.delete(listener);
+}
+
+export function getLastHeartbeatEvent(): HeartbeatEventPayload | null {
+  return lastHeartbeat;
+}