diff --git a/src/routes/+layout.svelte b/src/routes/+layout.svelte
index 2ce7a5ec..5b72e485 100644
--- a/src/routes/+layout.svelte
+++ b/src/routes/+layout.svelte
@@ -356,6 +356,21 @@ $effect(() => {
         navigator.serviceWorker.addEventListener('controllerchange', on_controller_change);
     }
 
+    // SW activate → reload bridge (parallel path to controllerchange above).
+    // WHY: controllerchange only fires in JS that has the listener registered.
+    // Tabs stuck on very old JS (pre-June-2026 builds) never set up that listener,
+    // so the new SW's postMessage from its activate event is the only way to reach
+    // them. The same had_controller guard prevents a spurious reload on fresh page
+    // loads where no SW was previously controlling the tab.
+    const on_sw_message = (event: MessageEvent) => {
+        if (event.data?.type === 'SW_ACTIVATE_RELOAD' && had_controller) {
+            window.location.reload();
+        }
+    };
+    if ('serviceWorker' in navigator) {
+        navigator.serviceWorker.addEventListener('message', on_sw_message);
+    }
+
     // Initialise PWA install prompt listener (captures beforeinstallprompt early).
     pwa_install.init();
 
@@ -443,6 +458,7 @@ $effect(() => {
         window.removeEventListener('message', handler);
         if ('serviceWorker' in navigator) {
             navigator.serviceWorker.removeEventListener('controllerchange', on_controller_change);
+            navigator.serviceWorker.removeEventListener('message', on_sw_message);
         }
     };
 });
diff --git a/src/service-worker.js b/src/service-worker.js
index e9be0988..52c84dac 100644
--- a/src/service-worker.js
+++ b/src/service-worker.js
@@ -33,18 +33,30 @@ self.addEventListener('install', (event) => {
 });
 
 self.addEventListener('activate', (event) => {
-    // Remove previous cached data from other screens
-    async function deleteOldCaches() {
+    async function activate() {
+        // Remove previous cached data from other deployments.
         for (const key of await caches.keys()) {
             if (key !== CACHE) await caches.delete(key);
         }
+
+        // Take control of all open tabs immediately after activation so they use
+        // the new service worker (and new cached assets) without needing a reload.
+        await self.clients.claim();
+
+        // Tell every open window tab to reload so it runs the new JS bundle.
+        // WHY: clients.claim() makes this SW the active controller but does not
+        // swap the JS already executing in those tabs. The `controllerchange`
+        // listener in +layout.svelte handles tabs already running new JS, but tabs
+        // stuck on old JS (e.g. from a build months ago, before that listener was
+        // added) never registered it. This postMessage reaches those tabs directly.
+        // Tabs that ignore it are still on old code and need a manual Full Reset.
+        const client_list = await self.clients.matchAll({ type: 'window' });
+        for (const client of client_list) {
+            client.postMessage({ type: 'SW_ACTIVATE_RELOAD' });
+        }
     }
 
-    event.waitUntil(deleteOldCaches());
-
-    // Take control of all open tabs immediately after activation so they use
-    // the new service worker (and new cached assets) without needing a reload.
-    self.clients.claim();
+    event.waitUntil(activate());
 });
 
 self.addEventListener('fetch', (event) => {