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chassis: auto-derive canonical/og:url from the surface's production base #471

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Merged
ChBrain merged 1 commit into from
Jul 4, 2026
Merged

chassis: auto-derive canonical/og:url from the surface's production base #471

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41 changes: 26 additions & 15 deletions src/layouts/BaseLayout.astro
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Original file line number Diff line number Diff line change
Expand Up @@ -18,19 +18,15 @@ import "../styles/tokens.css";
// the same `.book-*` classes instead of re-inlining its own copy.
import "../styles/book.css";
import "../styles/voices.css";
import { urlsFor } from "../lib/urls";

interface Props {
title: string;
description?: string;
// Absolute URL of this page's canonical. Opt-in, not auto-derived from
// `surface` below: src/lib/urls.ts (SurfaceUrls) maps *surface* -> production
// base, and for architecture/cultures/plays/misfits/writing that mapping is
// a clean strip-the-surface-prefix-and-prepend-the-base (their production
// base IS a subdomain root, one-to-one with the build folder). But the bare
// apex page (src/pages/index.astro, dist/index.html, surface -> "root") has
// no entry in SurfaceUrls at all - there's no production base to derive
// from for it. Rather than special-case that one page, canonical stays a
// per-page decision: pass it explicitly where it matters.
// Absolute URL of this page's canonical. Usually omitted: the layout
// derives it from the surface's PRODUCTION base (see below). Pass it only
// to override the derivation, or on the one page it can't cover (the bare
// apex placeholder, surface "root", which has no SurfaceUrls entry).
canonical?: string;
// Absolute URL to a social preview image. Presence upgrades twitter:card
// from "summary" to "summary_large_image" (the large-image card Twitter/X
Expand Down Expand Up @@ -65,6 +61,22 @@ const toSurfaceRoot = "../".repeat(Math.max(0, segments.length - 1)) || "./";
// this stamp, which is how a future routing leak (a subdomain serving the
// wrong surface) gets caught instead of silently 200ing. See issue 149.
const surface = segments[0] ?? "root";

// Canonical: an explicit prop wins; otherwise derive from the surface's
// production base. Deliberately urlsFor() (production), NOT the DEPLOY_ENV-
// switched URLS: a canonical is a statement of authority, not navigation.
// The same page is served from several doc roots (production subdomain,
// staging path prefix), and all copies must declare the production URL as
// canonical - that is what keeps the duplicates from competing in search.
// The mapping is sound for every surface in SurfaceUrls: each build folder
// deploys as its base's doc root, so production URL = base + the path below
// the surface folder (for main's nested cvi/privacy/contact pages this
// reproduces URLS.cvi/privacy/contact exactly). The bare apex placeholder
// (surface "root") has no entry and gets no canonical unless passed.
const productionBase = (urlsFor() as unknown as Record<string, string>)[surface];
const rest = segments.slice(1).join("/");
const canonicalUrl =
canonical ?? (productionBase ? productionBase + (rest ? `${rest}/` : "") : undefined);
---

<!doctype html>
Expand All @@ -75,17 +87,16 @@ const surface = segments[0] ?? "root";
<meta name="description" content={description} />
<meta name="x-surface" content={surface} />
<title>{title}</title>
{canonical && <link rel="canonical" href={canonical} />}
{canonicalUrl && <link rel="canonical" href={canonicalUrl} />}

<!-- Open Graph + Twitter. og:url only appears when `canonical` was passed
explicitly (see the Props.canonical comment above for why there's no
auto-derivation). og:image / the large-image twitter:card are opt-in
via `ogImage`. -->
<!-- Open Graph + Twitter. og:url mirrors the canonical (derived or
explicit; absent only on the bare apex placeholder). og:image / the
large-image twitter:card are opt-in via `ogImage`. -->
<meta property="og:title" content={title} />
<meta property="og:description" content={description} />
<meta property="og:type" content="website" />
<meta property="og:site_name" content="kaihacks" />
{canonical && <meta property="og:url" content={canonical} />}
{canonicalUrl && <meta property="og:url" content={canonicalUrl} />}
{ogImage && <meta property="og:image" content={ogImage} />}
<meta name="twitter:card" content={ogImage ? "summary_large_image" : "summary"} />
<link rel="icon" href={`${toSurfaceRoot}favicon.ico`} sizes="any" />
Expand Down