Inline backtick spans were converted to <code> only at the end of
mdToHtml, after the bare-URL autolink and <a>/allowed-HTML passes. A URL
inside inline code is preceded by a space, so the autolink wrapped it in
an <a> tag and swapped it for an ___ALLOWED_HTML_ placeholder, corrupting
commands like `irm http://127.0.0.1:3000/x`.
Extract inline code into placeholders before the link passes, mirroring
the existing fenced-code-block handling, and restore them last so
placeholders carried inside restored <a> blocks resolve. Escape the code
at extraction time since it now bypasses the global escape pass.
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