The existing-message overflow split path in stream_consumer.run() sealed the
first chunk via _send_or_edit(chunk) (finalize=False) then reset _message_id
to None — so that chunk was never edited again and never received the adapter's
final rich-text pass. On Telegram, MarkdownV2 formatting is applied on the
finalize edit, so early split messages of a long multi-part streamed reply
rendered raw markdown (##, **bold**, code fences) while only the last chunk
rendered correctly.
Fix: seal the overflow chunk with finalize=True so it gets its final
formatting pass before _message_id is cleared.
Salvaged from #32609 (the streaming-format portion only; the PR's send_draft
parse_mode change is already superseded on main, and its media-roots change
conflicts with the current denylist + recency-window delivery model).
454d6cbe52