fix(landing): fetch launcher downloads from live launcher.json on load

The build-time download buttons baked stale/placeholder URLs (the host has no
synced launcher.json, so the build fell back to launcher.example.json). Render
a skeleton at build time instead and fetch the live launcher.json client-side
once on page load (no polling) from
https://distribution.${BASE_DOMAIN}/launcher/launcher.json, building per-OS
buttons from files[]. On fetch error the skeleton clears.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

landing/src/pages/[...lang].astro

@@ -25,14 +25,11 @@ const launcherName = launcherManifest.product;
 const registerPath = LANG_REGISTER_PATH[locale];
 const accountPath = LANG_ACCOUNT_PATH[locale];
 
-// Per-OS download buttons (join step 2) from the synced manifest. Missing
-// manifest → empty builds → no buttons (the build never fails on it).
-const OS_LABELS: Record<string, string> = { windows: "Windows", macos: "macOS", linux: "Linux" };
-const launcherBuilds = launcherManifest.builds.map((b) => ({
-  label: b.label ?? `${OS_LABELS[b.os] ?? b.os}`,
-  hint: `${b.arch} · ${b.format}`,
-  url: b.url,
-}));
+// Per-OS download buttons (join step 2) are fetched client-side from the live
+// launcher.json on page load (no build-time baking, no polling) — see the
+// script below. We only pass the URL; buttons render into the #launcher-dl
+// skeleton. URL derives from the distribution subdomain.
+const launcherJsonUrl = `https://distribution.${site.baseDomain}/launcher/launcher.json`;
 
 // Build-time floating dust bits (index-derived, no runtime RNG).
 const dustBits = Array.from({ length: 16 }, (_, i) => {
@@ -158,15 +155,11 @@ const dustBits = Array.from({ length: 16 }, (_, i) => {
                 <span class="kicker">{t.join.s2.kicker}</span>
                 <h3>{t.join.s2.h.replace("{name}", launcherName)}</h3>
                 <p>{t.join.s2.p.replace(/\{name\}/g, launcherName)}</p>
-                {launcherBuilds.length > 0 && (
-                  <div class="actions">
-                    {launcherBuilds.map((b) => (
-                      <a class="mc-btn sm" href={b.url}>
-                        {b.label} <span class="hint">· {b.hint}</span>
-                      </a>
-                    ))}
+                <div class="actions" id="launcher-dl" data-src={launcherJsonUrl}>
+                  <span class="mc-btn sm dl-skeleton" aria-hidden="true"></span>
+                  <span class="mc-btn sm dl-skeleton" aria-hidden="true"></span>
+                  <span class="mc-btn sm dl-skeleton" aria-hidden="true"></span>
                 </div>
-                )}
               </div>
             </div>
           </div>
@@ -323,6 +316,35 @@ const dustBits = Array.from({ length: 16 }, (_, i) => {
         );
         els.forEach((el) => io.observe(el));
       }
+
+      // Launcher downloads — fetch the live launcher.json once on load (no
+      // polling) and render per-OS buttons into the #launcher-dl skeleton.
+      // launcher.json shape: { files: [{ name, os, arch, ext, url }] }.
+      const dl = document.getElementById("launcher-dl");
+      const src = dl?.dataset.src;
+      if (dl && src) {
+        const OS: Record<string, string> = { windows: "Windows", macos: "macOS", linux: "Linux" };
+        fetch(src, { cache: "no-store" })
+          .then((r) => (r.ok ? r.json() : Promise.reject(new Error(`HTTP ${r.status}`))))
+          .then((data) => {
+            const files = Array.isArray(data?.files) ? data.files : [];
+            const frag = document.createDocumentFragment();
+            for (const f of files) {
+              if (!f?.url) continue;
+              const a = document.createElement("a");
+              a.className = "mc-btn sm";
+              a.href = f.url;
+              a.append(`${OS[f.os] ?? f.os ?? "Download"} `);
+              const hint = document.createElement("span");
+              hint.className = "hint";
+              hint.textContent = `· ${[f.arch, f.ext].filter(Boolean).join(" · ")}`;
+              a.append(hint);
+              frag.append(a);
+            }
+            dl.replaceChildren(frag); // empty list → no buttons (skeleton cleared)
+          })
+          .catch(() => dl.replaceChildren()); // unreachable/error → clear skeleton
+      }
     </script>
   </body>
 </html>

landing/src/styles/main.css

@@ -207,6 +207,26 @@ section { position: relative; z-index: 1; }
 }
 .mc-btn.sm { font-size: 14px; padding: 10px 16px 12px; }
 
+/* Launcher download skeleton (placeholder while launcher.json loads). */
+.dl-skeleton {
+  min-width: 9.5rem;
+  color: transparent;
+  pointer-events: none;
+  background-image: linear-gradient(
+    90deg,
+    oklch(1 0 0 / 0.04),
+    oklch(1 0 0 / 0.14),
+    oklch(1 0 0 / 0.04)
+  );
+  background-size: 200% 100%;
+  animation: dl-shimmer 1.2s linear infinite;
+}
+.dl-skeleton::after { content: "\00a0"; } /* keep height when text is empty */
+@keyframes dl-shimmer {
+  from { background-position: 200% 0; }
+  to { background-position: -200% 0; }
+}
+
 /* ---- Copy-IP chip ---- */
 .ip-chip {
   display: inline-flex;