fix(telegram): preserve incident history html output

apps/api/tests/test_telegram_message_templates.py

@@ -53,6 +53,51 @@ def test_auto_repair_status_line_distinguishes_auto_resolved() -> None:
     assert "CPU 92%->30%" in result
 
 
+def test_telegram_html_chunks_preserve_complete_lines() -> None:
+    """歷史/詳情長訊息不得用 text[:500] 切壞 HTML tag。"""
+    lines = [
+        "📊 <b>事件歷史統計</b>",
+        "",
+        "<code>INC-20260513-79ED5E</code>",
+        "🧭 <b>DB Truth-chain</b>",
+        "階段: <code>blocked</code> / <code>manual_required</code>",
+    ] * 90
+
+    chunks = telegram_gateway_module._telegram_html_chunks(lines, limit=900)
+
+    assert len(chunks) > 1
+    assert all(len(chunk) <= 900 for chunk in chunks)
+    assert all(chunk.count("<code>") == chunk.count("</code>") for chunk in chunks)
+    assert all(chunk.count("<b>") == chunk.count("</b>") for chunk in chunks)
+
+
+@pytest.mark.asyncio
+async def test_send_html_line_message_falls_back_to_plain_text_on_parse_error(monkeypatch):
+    """Telegram HTML parse 400 時要送純文字 fallback，不可回報成歷史查詢失敗。"""
+    sent_requests = []
+    gateway = TelegramGateway()
+
+    async def fake_send_request(method, payload):
+        sent_requests.append((method, payload))
+        if payload.get("parse_mode") == "HTML":
+            raise telegram_gateway_module.TelegramGatewayError("HTTP error: 400")
+        return {"ok": True}
+
+    monkeypatch.setattr(gateway, "_send_request", fake_send_request)
+
+    await gateway._send_html_line_message(
+        ["📊 <b>事件歷史統計</b>", "階段: <code>blocked</code>"],
+        chat_id="chat",
+        failure_context="test_history",
+    )
+
+    assert len(sent_requests) == 2
+    assert sent_requests[0][1]["parse_mode"] == "HTML"
+    assert "parse_mode" not in sent_requests[1][1]
+    assert "<code>" not in sent_requests[1][1]["text"]
+    assert "blocked" in sent_requests[1][1]["text"]
+
+
 class TestTelegramMessageFormat:
     """測試現有 TelegramMessage 格式化"""