feat: use Telegram native Rich Message for assistant replies

Co-authored-by: MuziIsabel <MuziIsabel@users.noreply.github.com>

tests/client.test.ts

@@ -51,3 +51,24 @@ test('sendMessage can include reply_markup', async () => {
     inline_keyboard: [[{ text: 'A', callback_data: 'bind:1' }]],
   })
 })
+
+test('sendRichMessage posts native rich markdown body', async () => {
+  const calls: Array<{ url: string; body: Record<string, unknown> }> = []
+  const fetchImpl: typeof fetch = async (input, init) => {
+    calls.push({ url: String(input), body: JSON.parse(String(init?.body)) })
+    return new Response(JSON.stringify({
+      ok: true,
+      result: { message_id: 2, date: 0, chat: { id: 1, type: 'private' }, text: '# hi' },
+    }), { status: 200 })
+  }
+  const client = new TelegramClient('TOK', { fetch: fetchImpl })
+  await client.sendRichMessage(1, '# hi\n\n- a\n- b')
+  assert.match(calls[0]!.url, /\/botTOK\/sendRichMessage$/)
+  assert.deepEqual(calls[0]!.body, {
+    chat_id: 1,
+    rich_message: {
+      markdown: '# hi\n\n- a\n- b',
+      skip_entity_detection: true,
+    },
+  })
+})

tests/rich-format.test.ts

@@ -0,0 +1,31 @@
+import assert from 'node:assert/strict'
+import test from 'node:test'
+import {
+  RICH_MESSAGE_MAX_CHARS,
+  splitRichMarkdown,
+} from '../src/rich-format.ts'
+
+test('splitRichMarkdown keeps small markdown as one chunk', () => {
+  const markdown = '# 标题\n\n- a\n- b\n\n```js\nx\n```\n'
+  assert.deepEqual(splitRichMarkdown(markdown), [markdown])
+})
+
+test('splitRichMarkdown splits long plain text without losing content', () => {
+  const markdown = 'a'.repeat(RICH_MESSAGE_MAX_CHARS + 100)
+  const chunks = splitRichMarkdown(markdown)
+  assert.ok(chunks.length > 1)
+  assert.equal(chunks.join(''), markdown)
+})
+
+test('splitRichMarkdown keeps long fenced code blocks balanced', () => {
+  const opening = '```js\n'
+  const closing = '\n```'
+  const markdown = `${opening}${'x'.repeat(RICH_MESSAGE_MAX_CHARS + 1000)}${closing}`
+  const chunks = splitRichMarkdown(markdown)
+  assert.ok(chunks.length > 1)
+  for (const chunk of chunks) {
+    assert.ok(chunk.trimStart().startsWith('```'), 'chunk should start with a fence')
+    assert.ok(chunk.trimEnd().endsWith('```'), 'chunk should end with a fence')
+  }
+  assert.equal(chunks.join('').replace(/```js\n/g, '').replace(/\n```/g, ''), 'x'.repeat(RICH_MESSAGE_MAX_CHARS + 1000))
+})