First cut

ws/broadcast.js

@@ -0,0 +1,24 @@
+// Central registry of all active WebSocket connections.
+// Fastify-websocket exposes individual socket objects; we collect them here
+// so any part of the server can broadcast without importing fastify itself.
+
+/** @type {Set<import('ws').WebSocket>} */
+const clients = new Set();
+
+export function registerClient(socket) {
+  clients.add(socket);
+  socket.on('close', () => clients.delete(socket));
+}
+
+/**
+ * Broadcast a job update to every connected client.
+ * @param {object} payload  Plain object — will be JSON-serialised.
+ */
+export function broadcast(payload) {
+  const msg = JSON.stringify(payload);
+  for (const ws of clients) {
+    if (ws.readyState === 1 /* OPEN */) {
+      ws.send(msg);
+    }
+  }
+}