Function replace_site_nav 

pub fn replace_site_nav(
    html: &str,
    nav: &[NavEntry],
    current_href: &str,
) -> Option<String>

Replace the <nav class="sitenav">…</nav> block in a hand-written page with the bar the renderer computes, returning None when the page carries no such block.

Why this exists

website/public/index.html is the one page of roteiro.dev nothing renders — it is copied verbatim — and it used to carry a hand-maintained copy of the list the renderer derives from site-order (issue #508). Adding docs/SERVING.md appeared in every rendered page’s bar automatically and had to be typed into the landing page by hand.

The failure that made it worth removing rather than remembering is silent and points the wrong way: a new page is published, reachable, and linked from every page except the front one. Nothing errors and roteiro check passes, because everything that is there resolves.

That is also why no link auditor could have caught it, and why none will catch the next one of its shape. The defect is a link that does not exist; auditing what is there cannot find what is missing. This removes the possibility instead — after this, the landing page has no independent list to disagree with. What still guards the seam is the_landing_page_carries_the_bar_the_renderer_emits, which now checks that the replacement happened: a landing page whose marker was renamed away keeps its stale bar silently, and that test is what fails.

Why None rather than an error

A landing page with no sitenav is not claiming a bar, and a site is allowed not to have one — every render docs fixture writes a one-line index.html. The caller leaves such a page alone.