_fetch_tweet did url.replace("x.com", "twitter.com") over the whole URL,
so "x.com" in the path or query was rewritten too (a ?next= link, or a
handle like dropbox.com_fan becoming dropbotwitter.com_fan), and an
uppercase X.COM host was missed. Match and rewrite the host only, the
same way _detect_url_type classifies it.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>