Custom marked renderer wraps fenced code blocks in a .code-block-wrapper
div containing a language label badge (top-right) and a copy button.
The language label shows the fenced language identifier in uppercase.
A delegated click handler on the document root intercepts clicks on
[data-copy-code] buttons, reads the sibling <code> element's text
content, writes it to the clipboard, and shows a "Copied!" / "Failed"
confirmation that auto-reverts after 1.5 seconds. Delegated handling
is necessary because code blocks are rendered via dangerouslySetInnerHTML
and don't participate in React's synthetic event system.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
teernisse
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