server : remove the built-in UI's service worker when the UI is not served (#29565)

With --path or --no-ui, /sw.js returned 404, and a 404 does not remove a service worker, so browsers kept showing the cached built-in UI. Serve a worker that unregisters itself, clears its caches and reloads open tabs. A sw.js in the --path folder is still served first.

Assisted-by: Claude Opus 5.5

tools/server/server-http.cpp

@@ -470,6 +470,23 @@ bool server_http_context::init_listener(const common_params & params) {
 #endif
         }
     }
+
+    // a browser that used the built-in UI keeps its service worker, so it shows the old UI even after the UI is replaced or disabled
+    // answer the worker's update check with a worker that removes itself; a sw.js in public_path is served first
+    if (!params.ui || !params.public_path.empty()) {
+        srv->Get(params.api_prefix + "/sw.js", [](const httplib::Request &, httplib::Response & res) {
+            static constexpr const char * sw_remove_js = R"(
+self.addEventListener('install', () => self.skipWaiting());
+self.addEventListener('activate', (e) => e.waitUntil((async () => {
+    await self.registration.unregister();
+    for (const key of await caches.keys()) await caches.delete(key);
+    for (const c of await self.clients.matchAll({ type: 'window' })) c.navigate(c.url);
+})()));
+)";
+            res.set_header("Cache-Control", "no-cache");
+            res.set_content(sw_remove_js, "application/javascript");
+        });
+    }
     return true;
 }