- Fix critical plain-text fallback that was sending raw HTML tags to
users: keep raw markdown available for the fallback path
- Extract TELEGRAM_HTML_MAX_LEN (4096) constant to replace hardcoded
magic number and document the difference from TELEGRAM_MAX_MESSAGE_LEN
- Add fallback to _send_text for extra HTML chunks when HTML parse fails
- Add missing @pytest.mark.asyncio decorator on
test_send_delta_stream_end_html_expansion_does_not_overflow