OP, please clean the LLM comments out of your html. You're gonna get flamed for that.

Case in point, staring on line 16:

  The one place a domain is hardcoded, and it has to be.

  Two hosts serve identical content - culdesac.site and the vercel.app
  subdomain, which stays working alongside on purpose. To a search engine
  that is duplicate content, and without this it picks a winner itself and
  may well pick the wrong one. A canonical URL is absolute by definition,
  so this cannot be relative the way the internal navigation is.

  If the primary domain ever changes, it changes here and in
  public/sitemap.xml and public/robots.txt together. check-canonical fails
  the build if those three disagree.
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