Check that every small Markdown source parses, serializes and parses again to the same document, and that a streamed parse that continues its previous result equals a fresh parse at every chunking, over the plugins of the Markdown test editor. Use before and after changing packages/platejs/src/markdown/lib or another file in its coverage record, when the markdown-round-trip step of pnpm check fails, or when fixing a Markdown or streaming bug a seed or a tester found.