Markdown source can never reach the reader as markup

A markdown-to-HTML conversion usually runs over text a language model wrote, so the encoding is a safety boundary rather than a formatting nicety. Encoding the whole input once, before any block or inline pattern is applied, is the arrangement that makes the promise hold on every arm: escaping at each emission point has been shown to miss the blocks a converter rebuilds from its buffer, and to miss any block whose first character is already a tag.