markdown: nested code fences

♠ Problem statement : a code block that quotes a markdown file swallows the first closing fence it meets, which is the inner one. The ADRs and LLMs post quotes a README.md that itself contains a fenced template. Written naively: ```markdown # README Use this template: ```markdown # ADR-NNNN: Title ``` That was the template. ``` The CommonMark spec says who wins: The content of the code block…