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>

dist/esm/messages/build.js

@@ -0,0 +1,124 @@
+// Every message the bridge publishes, built from plain values. Nothing here reads the clock or makes an id unless
+// the caller leaves messageId or a time out, so a test that passes both compares whole objects.
+import { randomUUID } from "crypto";
+import { errorNamespace } from "./errors.js";
+import { isoTime } from "./property.js";
+/** A message that would be dropped on its way to Alexa, refused where it is built. */
+export class MessageError extends Error {
+    constructor(endpointId, problem) {
+        super(`${endpointId}: ${problem}`);
+        this.endpointId = endpointId;
+        this.problem = problem;
+        this.name = "MessageError";
+    }
+}
+// The fields in the order of the examples
+function header(namespace, name, fields) {
+    return {
+        namespace,
+        name,
+        ...(fields.instance ? { instance: fields.instance } : {}),
+        messageId: fields.messageId ?? randomUUID(),
+        ...(fields.correlationToken !== undefined ? { correlationToken: fields.correlationToken } : {}),
+        payloadVersion: fields.payloadVersion ?? "3",
+    };
+}
+/**
+ * The answer to a directive (alexa-response.html, "Synchronous response"). An endpoint with nothing to report
+ * answers with an empty list of properties, not without a context (state-reporting-for-smart-home-addons.html,
+ * "Directive response example for a property that isn't retrievable").
+ */
+export function response(fields) {
+    return {
+        event: {
+            header: header(fields.namespace ?? "Alexa", fields.name ?? "Response", fields),
+            endpoint: { endpointId: fields.endpointId },
+            payload: fields.payload ?? {},
+        },
+        context: { properties: [...(fields.context ?? [])] },
+    };
+}
+/** The answer to ReportState: every retrievable property of the endpoint. */
+export function stateReport(fields) {
+    return response({ ...fields, name: "StateReport", namespace: "Alexa", payload: {} });
+}
+/**
+ * "The directive arrived, the answer follows": no context, the state is in the Response that follows
+ * (alexa-response.html, "Deferred response example").
+ */
+export function deferredResponse(fields) {
+    const { estimatedDeferralInSeconds } = fields;
+    return {
+        event: {
+            header: header("Alexa", "DeferredResponse", fields),
+            endpoint: { endpointId: fields.endpointId },
+            payload: estimatedDeferralInSeconds === undefined ? {} : { estimatedDeferralInSeconds },
+        },
+    };
+}
+/** The answer to a directive the endpoint could not follow (alexa-errorresponse.html). */
+export function errorResponse(fields) {
+    return {
+        event: {
+            header: header(fields.namespace ?? errorNamespace(fields.type), "ErrorResponse", fields),
+            endpoint: { endpointId: fields.endpointId },
+            payload: { type: fields.type, message: fields.message, ...fields.extra },
+        },
+    };
+}
+const sameProperty = (a, b) => a.namespace === b.namespace && a.name === b.name && (a.instance ?? "") === (b.instance ?? "");
+/**
+ * A change of state nobody asked for. The header has no correlationToken (message-guide.html, "Header object").
+ * A property that changed is left out of the context: it is reported in one of the two (same page, "Context
+ * object"). Throws MessageError when nothing changed: Alex2MQTT drops such a report without a word.
+ */
+export function changeReport(fields) {
+    const { endpointId, changed, context = [] } = fields;
+    if (changed.length === 0) {
+        throw new MessageError(endpointId, "a ChangeReport needs at least one property that changed, this one has none. "
+            + "Add the changed property before unchanged(), or send no report when nothing changed");
+    }
+    return {
+        event: {
+            header: header("Alexa", "ChangeReport", { messageId: fields.messageId }),
+            endpoint: { endpointId },
+            payload: { change: { cause: { type: fields.cause ?? "PHYSICAL_INTERACTION" }, properties: [...changed] } },
+        },
+        context: { properties: context.filter((property) => !changed.some((other) => sameProperty(property, other))) },
+    };
+}
+/** The answer to Activate and Deactivate of a scene (alexa-scenecontroller.html). */
+export function sceneEvent(fields) {
+    return {
+        event: {
+            header: header("Alexa.SceneController", fields.activated ? "ActivationStarted" : "DeactivationStarted", fields),
+            endpoint: { endpointId: fields.endpointId },
+            payload: { cause: { type: fields.cause ?? "VOICE_INTERACTION" }, timestamp: isoTime(fields.timestamp) },
+        },
+        context: {},
+    };
+}
+/** Somebody rang (alexa-doorbelleventsource.html). */
+export function doorbellPress(fields) {
+    return {
+        event: {
+            header: header("Alexa.DoorbellEventSource", "DoorbellPress", { messageId: fields.messageId }),
+            endpoint: { endpointId: fields.endpointId },
+            payload: { cause: { type: fields.cause ?? "PHYSICAL_INTERACTION" }, timestamp: isoTime(fields.timestamp) },
+        },
+    };
+}
+/** An event of a button or a sensor that routines start on (alexa-simpleeventsource.html). */
+export function simpleEvent(fields) {
+    return {
+        event: {
+            header: header("Alexa.SimpleEventSource", "Event", {
+                instance: fields.instance,
+                messageId: fields.messageId,
+                payloadVersion: "1.0",
+            }),
+            endpoint: { endpointId: fields.endpointId },
+            payload: { id: fields.id, timestamp: isoTime(fields.timestamp) },
+        },
+    };
+}