The corpus

One directory per contract kind:

round-trip/ — <name>.json + <name>.md: the markdown adfToMarkdown must emit for that document, byte for byte, and that markdownToAdf must read back to it (AGENTS.md §2). Grouped by node family: commonmark-subset/, block-nodes/, inline-nodes/, opaque-carry/, combinations/.
normalization/ — <name>.md + <name>.json: markdown input, and the document markdownToAdf must build from it. One-way; the markdown is not canonical.
errors/ — <name>.md: markdown input that must not convert. A <name>.error beside it pins which error.
real-payloads/ — <name>.json: sanitized live ADF, round-tripped ADF→markdown→ADF. No expected markdown.

JSON is editor-normal (AGENTS.md §2), two-space indent, keys sorted.