test: split the 1.5.2 suite into a harness and per-topic files

test/helpers/harness.js holds the aedes broker, the Alexa-side watcher, until() and the cleanups, plus directive(),
connected() and setup(), which the old file spelled out in each test. test/alex2node.test.js (194 lines, 8 tests)
becomes connection, discovery, directives, change-report and typings.

The 50-line round-trip test is cut at its topic boundaries and the duplicate-endpointId test no longer carries the
thermostat discovery check, so a failure names a case: 8 tests become 15, every 1.5.2 assertion kept. Four checks
are stricter: the "directive" event is compared whole, the StateReport is checked for its token and properties, the
Celsius conversion covers lowerSetpoint as well as temperature, and a duplicate endpointId is listed once.

No change to src/ or dist/. npm test: 15 pass in 0.9 s.

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

test/typings.test.js

@@ -0,0 +1,37 @@
+"use strict";
+// The declarations tracked in dist/: what a TypeScript consumer compiles against.
+const { test } = require("node:test");
+const assert = require("node:assert/strict");
+const fs = require("node:fs");
+const path = require("node:path");
+const { ActionMapping, AlexaActions, AlexaStatusMessage, EndpointHealth } = require("../dist/index.js");
+
+const DIST = path.join(__dirname, "..", "dist");
+const MODULES = [
+  "index", "Alex2Node", "Device", "AlexaInterface", "AlexaStatusMessage", "AlexaErrorResponse", "ActionMapping",
+  "DisplayCategory",
+];
+const declaration = (name) => fs.readFileSync(path.join(DIST, `${name}.d.ts`), "utf8");
+
+test("1.5.2 typings: dist ships declarations, ActionMapping's payload is optional, addHealthProp takes the enum or the string", () => {
+  for (const name of MODULES) assert.ok(fs.existsSync(path.join(DIST, `${name}.d.ts`)), `dist/${name}.d.ts`);
+
+  // The declaration text itself: a revert in src/ would rebuild narrower types, and the runtime checks below would
+  // not notice.
+  assert.match(declaration("ActionMapping"), /constructor\(actions: AlexaActions\[\], directiveName: string, directivePayload\?: string\);/);
+  assert.match(declaration("AlexaStatusMessage"), /addHealthProp\(health: EndpointHealth \| `\$\{EndpointHealth\}`, uncertaintyInMs\?: number\): this;/);
+  assert.match(declaration("AlexaInterface"), /addSupportedModes\(modes: Array<string \| SupportedMode>\): void;/);
+  assert.match(declaration("index"), /export type \{ SupportedMode \} from "\.\/AlexaInterface";/);
+
+  assert.deepEqual(new ActionMapping([AlexaActions.Close], "TurnOn").toJSON(), {
+    "@type": "ActionsToDirective",
+    actions: ["Alexa.Actions.Close"],
+    directive: { name: "TurnOn" },
+  });
+  const health = (h) => {
+    const message = new AlexaStatusMessage("ct", "root", "e", null).addHealthProp(h).toJSON();
+    return message.context.properties[0].value;
+  };
+  assert.deepEqual(health(EndpointHealth.OK), { value: "OK" });
+  assert.deepEqual(health("UNREACHABLE"), { value: "UNREACHABLE" });
+});