messages: pure builders for every event the bridge sends

src/messages builds Response, StateReport, DeferredResponse, ErrorResponse, ChangeReport and the scene, doorbell
and simple events from plain values; messageId and times are parameters, so a test compares whole objects.
StateBuilder collects properties checked by the descriptors, AlexaError and AlexaErrors carry the payload fields
of an error type. AlexaStatusMessage and AlexaErrorResponse move to src/compat and are written on the builders.
On the wire, against 1.5.2: a DeferredResponse has no context key, a ChangeReport has no correlationToken, the
namespace of an ErrorResponse follows its type, and a ChangeReport without a changed property is not published:
send() resolves "" and the bridge reports an error that names the endpoint.
143 tests pass (108 before).

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

src/compat/AlexaErrorResponse.ts

@@ -0,0 +1,64 @@
+import { randomUUID } from "crypto";
+import type { MqttClient } from "mqtt";
+import { errorResponse } from "../messages/build.js";
+import { AlexaErrors } from "../messages/errors.js";
+import type { AlexaError } from "../messages/errors.js";
+import type { ErrorResponseMessage } from "../messages/types.js";
+
+/** An ErrorResponse as 1.x builds it: device.getErrorMessage(token), setErrorMessage(), send(). */
+export class AlexaErrorResponse {
+  // Sent when setErrorMessage() was not called: 1.x published an empty payload, which is no ErrorResponse to Alexa
+  private error: AlexaError = AlexaErrors.of("INTERNAL_ERROR", "the device answered with an error and did not say which");
+  private namespace?: string;
+  // One id for the message, however often toJSON() is called
+  private readonly messageId = randomUUID();
+  /** Where a failed publish is reported (set by the Device that built this message, 1.5.2): send() never rejects. */
+  public onPublishError?: (err: Error) => void;
+
+  constructor(
+    private readonly correlationToken: string,
+    private readonly rootTopic: string,
+    private readonly endpointId: string,
+    private readonly mqttClient: MqttClient
+  ) {}
+
+  /**
+   * The error to answer with. otherParams are the fields the type adds to the payload (validRange). The header
+   * carries the namespace the type is documented under, Alexa.ThermostatController for THERMOSTAT_IS_OFF;
+   * options.namespace names another.
+   */
+  setErrorMessage(
+    type: string,
+    message: string,
+    otherParams: Record<string, any> = {},
+    options: { namespace?: string } = {}
+  ): void {
+    this.error = AlexaErrors.of(type, message, otherParams);
+    this.namespace = options.namespace;
+  }
+
+  toJSON(): ErrorResponseMessage {
+    const { type, alexaMessage, extra } = this.error;
+    return errorResponse({
+      endpointId: this.endpointId,
+      messageId: this.messageId,
+      correlationToken: this.correlationToken,
+      type,
+      message: alexaMessage,
+      extra,
+      namespace: this.namespace ?? this.error.namespace,
+    });
+  }
+
+  /** Resolves with the topic published to, or "" when the publish failed. Never rejects. */
+  send(sendAsync = false): Promise<string> {
+    const topic = `${this.rootTopic}/${this.endpointId}/${sendAsync ? "deferredResponse" : "alexaResponce"}`; // "alexaResponce" is how Alex2MQTT and Alex2ESP spell the topic
+    return new Promise((resolve) => {
+      this.mqttClient.publish(topic, JSON.stringify(this.toJSON()), (err) => {
+        if (!err) return resolve(topic);
+        if (this.onPublishError) this.onPublishError(err); // -> the bridge's "error" event (when somebody listens)
+        resolve(""); // 1.5.1 rejected here, and an un-caught send() then killed the host on any broker hiccup
+      });
+    });
+  }
+}