If you buffer starting with the ( character, then you'd still send the [text] part of the link, and worst case is that with no matching ) character to close the link, you end up buffering the remainder of the response. Even still, the last step is "flush any buffered text to the client", so the remainder of the response will be transmitted eventually in a single chunk.
There are some easy wins that could improve this further: line endings within links are generally not valid markdown, so if the code ever sees \n then just flush buffered text to the client and reset the state to TEXT.
Comments
If you buffer starting with the ( character, then you'd still send the [text] part of the link, and worst case is that with no matching ) character to close the link, you end up buffering the remainder of the response. Even still, the last step is "flush any buffered text to the client", so the remainder of the response will be transmitted eventually in a single chunk.
There are some easy wins that could improve this further: line endings within links are generally not valid markdown, so if the code ever sees \n then just flush buffered text to the client and reset the state to TEXT.