diff --git a/server/server.js b/server/server.js
index c2ea82f..9ff07b2 100644
--- a/server/server.js
+++ b/server/server.js
@@ -392,11 +392,18 @@ app.get('/sw.js', (c) => {
       return c.text('Service worker not found', 404);
     }
   }
-  // Inject the build tag: replace the placeholder with the real value.
+  // Inject the build tag: replace the whole fallback expression with the
+  // real value. Matched by REGEX, not an exact string — an exact match broke
+  // the moment the fallback literal in sw.js was bumped ('v1.0.3' → 'v1.0.4'),
+  // after which the replacement silently did nothing, the SW version froze,
+  // and clients never saw another update no matter how many times we deployed.
   const src = _swSource.replace(
-    "typeof __BUILD_TAG__ !== 'undefined' ? __BUILD_TAG__ : 'v1.0.3'",
+    /typeof __BUILD_TAG__ !== 'undefined' \? __BUILD_TAG__ : '[^']*'/,
     JSON.stringify(BUILD_TAG)
   );
+  if (src === _swSource) {
+    console.error('[sw] BUILD_TAG injection failed — placeholder not found in sw.js');
+  }
   return c.text(src, 200, {
     'Content-Type': 'application/javascript; charset=utf-8',
     'Cache-Control': 'no-store, no-cache, must-revalidate',