fix: emit autolink content verbatim without escapes

[SAY-5]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything or linked relevant results below
• I made sure the docs are up to date
• I included tests (or that’s not needed)

Description of changes

Autolink content is interpreted literally per CommonMark, so the serializer no longer routes it through phrasing escaping, which was doubling backslashes (and escaping other characters) in the URL on round-trip. Closes #73.

[SAY-5]

The CI failure looks unrelated to this change: c8 (via yargs) throws ReferenceError: require is not defined on Node 26, and the Node 18 job reports # fail 0 before the matrix is cancelled. Tests pass locally with npm run test-api.

[wooorm]

Hi! Did you see the code around it? e.g.:

  if (formatLinkAsAutolink(node, state)) {
    // Hide the fact that we’re in phrasing, because escapes don’t work.
    const stack = state.stack
    state.stack = []

Can you explain what you ran into?

[github-actions]

Hi! Thanks for taking the time to contribute! This has been marked by a maintainer as needing more info. It’s not clear yet whether this is an issue. Here are a couple tips:

• Spend time framing the pull request! The more time you put into it, the more we will
• Often, maintainers respond with why for several back and forths; rubber duck debugging might help avoid that
• Folks posting issues sometimes fall for xy problems: asking for a certain solution instead of raising the root problem

Thanks,
— bb

[SAY-5]

Yes, the stack clearing handles the unsafe patterns, since those are filtered through patternInScope. What it doesn't cover is escapeBackslashes() at the bottom of lib/util/safe.js, which runs unconditionally and doubles a backslash that sits before ASCII punctuation (here the closing > passed as config.after). So on main, fromMarkdown('aa:\\') gives a link whose text is 'aa:\', and toMarkdown emits 'aa:\\\\'; that round-trip is what the added test covers.