Fix OG image localhost fallback; swap frontmatter demo image (#102)

* Fix OG image URL falling back to localhost on prod build

makePublicURL() returned http://localhost:3000/ for prod deploys:
VERCEL_URL is unset on GitHub Actions, and DEPLOYMENT_ALIAS is only
written to $GITHUB_ENV after vercel build runs, so neither is available
at build time. Add a main-branch CI guard that returns the canonical URL.

* Swap frontmatter demo image to huike-thinking.webp

* Update visual snapshots for frontmatter demo image swap

* Use CI-native linux render for frontmatter snapshot

The jammy-container baseline differed ~5% from ubuntu-latest's webp
render (above the 2% tolerance). Replace the two linux baselines with
CI's own rendered output so they match the CI environment exactly.

Author: hasparus

astro.config.ts

@@ -89,6 +89,13 @@ function makePublicURL() {
   const VERCEL_URL = process.env.VERCEL_URL;
   const DEPLOYMENT_ALIAS = process.env.DEPLOYMENT_ALIAS;
 
+  // Prod build on CI: DEPLOYMENT_ALIAS isn't written to the env until *after*
+  // `vercel build` runs, so detect the main-branch CI build directly and return
+  // the canonical URL. Without this, OG image URLs fall through to localhost.
+  if (process.env.CI && process.env.GITHUB_REF === "refs/heads/main") {
+    return site;
+  }
+
   // If the site is built on vercel, we can just use VERCEL_URL.
   if (VERCEL_URL) return VERCEL_URL;
 

e2e/visual-regression.spec.ts-snapshots/features-post-with-frontmatter-desktop-darwin.png

@@ -1,7 +1,7 @@
 ---
 title: "Frontmatter"
 date: "2022-10-04"
-img: "/frontmatter/pic.jpg"
+img: "/frontmatter/huike-thinking.webp"
 ---
 
 Imagine that this post was written a long time in the past in a paper notebook,
@@ -20,7 +20,7 @@ Better read [./minimal-note](./minimal-note).
 ---
 title: "Frontmatter"
 date: "2022-10-04"
-img: "/frontmatter/pic.jpg"
+img: "/frontmatter/huike-thinking.webp"
 ---
 
 Imagine that this post was written a long time in the past in a paper notebook,