feat(github-code): block to embed GitHub source with line ranges

[markdaugherty]

Summary

Adds a new github-code block that embeds source code from a GitHub repository, with an optional line-number range.

• Author pastes a standard GitHub blob URL (e.g. https://github.com/owner/repo/blob/main/path/file.js#L10-L20) — or a GitHub "Copy permalink" URL with column numbers (#L10C1-L20C5) — or just a bare URL with no link markup; the block parses owner/repo/ref/path and the optional line range.
• A bare blob URL alone in its own paragraph is also auto-blocked into a github-code block, so authors can just drop the link in without building the block table by hand. Links inside prose, lists, blockquotes, or authored block cells are left untouched.
• Fetches the file from raw.githubusercontent.com, slicing to the requested lines (whole file if no range), and strips the trailing blank line raw GitHub files end with.
• Renders into pre > code and highlights via the existing locally-hosted highlight.js (/libs/highlight/, atom-one-dark), loaded lazily on scroll-into-view — mirroring the guide-template code-block pattern.
• Reuses the shared addCopyButtonsToCodeBlocks helper (now exported from scripts.js) for the copy button.
• Header shows the file path (percent-decoded), a ref badge (branch/tag, or a truncated 7-char SHA for full commit hashes), the line range, and a "View on GitHub" link.
• Snippets over 40 lines collapse behind a "Show all N lines" / "Show fewer lines" toggle.
• Falls back to a styled error message (linking back to GitHub) on an invalid/out-of-range line fragment or a fetch failure, and to a plain "View code on GitHub" link for URLs that aren't a recognizable GitHub blob URL.

Preview

https://feature-github-code-block--helix-website--adobe.aem.page/drafts/mdaugherty/github-code-block

Notes

• The bundled highlight.js build now registers bash, css, javascript, ruby, yaml, xml (html/svg), json — xml and json grammars were appended from the official 11.7.0 cdnjs build so HTML and JSON snippets get real token coloring instead of just the themed background. Other languages (python, typescript, java, etc.) still render in the themed panel without color; the block applies the hljs class itself so the background stays consistent and skips the highlighter when a grammar isn't available (avoids console warnings).
• addCopyButtonsToCodeBlocks() scans the document and is idempotent (skips pres that already have a button), matching the guide-template behavior.
• Fixed a race where multiple github-code blocks becoming visible at once could each call the shared loadScript helper independently; since that helper resolves as soon as it sees a matching <script> tag (even one still loading), later blocks could silently skip highlighting. The block now memoizes a single load promise per page.

Testing

• ✅ Verified every variant (line range, single line, whole file, long-file toggle, permalink with column numbers, commit-SHA ref truncation, invalid line range, invalid URL, autoblocked bare link, prose link left alone, json/xml highlighting) renders correctly with copy buttons and no console errors (Playwright), against local draft content.
• ✅ npm run lint clean for JS and CSS.

🤖 Generated with Claude Code

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Commits

• 71e0e96 ✅ (latest)
• 6c0e98a ✅
• ab60664 ✅
• 0b656b1 ✅
• 8dc3b89 ✅
• 9aca6ee ✅
• b8886ed ✅

[aem-code-sync]

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