The corpus
<name>.json is an ADF document; <name>.md is the markdown adfToMarkdown must emit for it,
byte for byte including the trailing newline, and that markdownToAdf must read back to that same
document (AGENTS.md §2). Directories mirror spec/flavour.md's sections.
The JSON is editor-normal — empty attrs, marks and content as the absent key, adjacent
identical-mark text nodes merged — two-space indent, keys sorted.