Add automatic Threads link replies and sunrise preview card

tests/threads.test.ts

@@ -2,7 +2,25 @@ import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import { calculateSun } from '../src/astronomy/sunCalculator.ts';
 import { observer } from '../src/config/observer.ts';
-import { dailySchedule, publishImage, publishCarousel } from '../server/threads/publisher.ts';
+import { dailySchedule, publishImage, publishCarousel, publishReply } from '../server/threads/publisher.ts';
+
+test('reply targets the published parent and attaches a preview link, claiming before publish', async () => {
+  const replies = [{ id: 'reply-container' }, { status: 'FINISHED' }, { id: 'reply' }];
+  let claimed = false;
+  const id = await publishReply('token', 'parent-post', 'Visit us', 'https://sunrise.horoli.kr', async () => {
+    claimed = true;
+  }, async (url, init) => {
+    const params = init?.body as URLSearchParams;
+    if (String(url).endsWith('/me/threads')) {
+      assert.equal(params.get('reply_to_id'), 'parent-post');
+      assert.equal(params.get('link_attachment'), 'https://sunrise.horoli.kr');
+      assert.equal(params.get('media_type'), 'TEXT');
+    }
+    if (String(url).endsWith('/me/threads_publish')) assert.ok(claimed);
+    return new Response(JSON.stringify(replies.shift()));
+  }, async () => {});
+  assert.equal(id, 'reply');
+});
 
 test('schedule uses the Korean date and existing SunCalc sunrise', () => {
   const now = new Date('2026-11-01T18:00:00Z');