bridge: a discovery request that arrives twice is answered once

A broker that mirrors another delivers every message twice, and the bridge
answered both copies of a discovery request. A request is now remembered
by its messageId for 60 s, as a directive is, and its copy is dropped with
a log line. The messageId is read from the header of the Discover
directive or from the request itself when that is the header alone.
A request without a messageId is answered every time, as before.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

dist/esm/Alex2Node.js

@@ -14,6 +14,20 @@ const DESCRIBED = [
     "description", "manufacturerName", "manufacturer", "model", "serialNumber", "firmwareVersion", "softwareVersion",
     "customIdentifier", "cookie",
 ];
+// The messageId of a discovery request: in the header of the Discover directive, or beside the namespace and the
+// name when the request is the header alone. undefined for a request without one, which is answered every time.
+function requestId(text) {
+    let request;
+    try {
+        request = JSON.parse(text);
+    }
+    catch {
+        return undefined;
+    }
+    const header = request?.directive?.header ?? request?.header ?? request;
+    const { messageId } = (typeof header === "object" && header !== null ? header : {});
+    return typeof messageId === "string" ? messageId : undefined;
+}
 /**
  * The Alexa-to-MQTT bridge: one broker connection for a user's root topic, a set of registered devices, discovery and
  * directive dispatch.
@@ -118,6 +132,11 @@ class Alex2MQTT extends EventEmitter {
         this.log(`MQTT Message Received`, { topic, payload: text });
         try {
             if (topic === topics.discover(this.rootTopic)) {
+                const messageId = requestId(text);
+                if (messageId !== undefined && this.dispatcher.arrivedBefore("", messageId)) {
+                    this.log(`the discovery request ${messageId} is dropped: it arrived before`);
+                    return;
+                }
                 await this.answerDiscovery();
                 return;
             }