fix(core/markdown): restore data-include markdown rendering with marked v16

[Copilot]

Upgrades marked 12→16. The new version is stricter CommonMark-compliant: HTML indented 4+ spaces is treated as a code block, not an HTML block. This broke data-include-format="markdown" when combined with format: "markdown" — rendered section content ended up escaped inside <pre><code> blocks.

Changes

Renderer API (code, image, heading)

marked v16 changed renderer method signatures from positional args to token objects:

// v12
code(text, infoString, isEscaped) { ... }
// v16
code({ text, lang, escaped }) { ... }

Indentation normalization (normalizeIndent)

When data-include renders markdown into a <section>, the resulting HTML has lines at column 0 (<ol>, <li>, etc.). The old reindent() used minimum indentation across all lines — inner content at col 0 made leastIndent = 0, leaving outer sections at 8–10 spaces untouched. marked v16 then treated those sections as indented code blocks.

Replaced reindent() in markdownToHtml() with a local normalizeIndent() that strips based on the first non-empty line's indentation rather than the minimum. This correctly removes the outer document indentation regardless of how inner rendered-HTML content is indented.

// old: min indent across all lines → 0 when inner HTML has col-0 lines
const leastIndent = Math.min(...indents);
// new: first non-empty line's indent → correctly strips outer structure
const firstIndent = lines[0].search(/[^\s]/);
const prefix = " ".repeat(firstIndent);
return lines.map(s => (s.startsWith(prefix) ? s.slice(firstIndent) : s)).join("\n");

---

🔒 GitHub Advanced Security automatically protects Copilot coding agent pull requests. You can protect all pull requests by enabling Advanced Security for your repositories. Learn more about Advanced Security.