diff --git a/web/vite.config.ts b/web/vite.config.ts
index c20b0fee..e80dadf0 100644
--- a/web/vite.config.ts
+++ b/web/vite.config.ts
@@ -13,6 +13,9 @@ const tokensPlugin = {
 // rendered index.html so the runtime Go server can substitute per-
 // instance branding. In dev (`vite dev`), the marker stays as a
 // comment and the SPA falls back to the literal app.html title.
+// `enforce: 'post'` ensures this runs after SvelteKit's own
+// transformIndexHtml so %sveltekit.head% is already expanded into
+// hydration markup before our anchors are rewritten.
 const injectGoTokensPlugin = {
   name: 'minstrel-inject-go-tokens',
   apply: 'build' as const,
@@ -29,6 +32,17 @@ const injectGoTokensPlugin = {
     <meta name="theme-color" media="(prefers-color-scheme: dark)" content="#14171A">
     <meta name="theme-color" media="(prefers-color-scheme: light)" content="#F8F5EE">
     <script>window.__MINSTREL__ = { appName: "{{ .AppName }}", description: "{{ .Description }}" };</script>`;
+
+    // Fail loudly if either anchor drifts. A silent .replace() no-op
+    // would ship a build with un-substituted Go template tokens missing,
+    // and the runtime brand override would silently break — exactly the
+    // class of regression a build-time plugin should catch.
+    if (!html.includes('<title>Minstrel</title>')) {
+      throw new Error('minstrel-inject-go-tokens: <title>Minstrel</title> anchor missing from rendered index.html');
+    }
+    if (!html.includes('<!-- MINSTREL_TOKENS -->')) {
+      throw new Error('minstrel-inject-go-tokens: <!-- MINSTREL_TOKENS --> anchor missing from app.html');
+    }
     return html
       .replace('<title>Minstrel</title>', titleTag)
       .replace('<!-- MINSTREL_TOKENS -->', headBlock);