feat(callback_host): close helper page on Drop via browser WS

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src/browser/callback_host.rs

@@ -324,6 +324,13 @@ impl BrowserCallbackExecutor for LiveBrowserCallbackHost {
 
 impl Drop for LiveBrowserCallbackHost {
     fn drop(&mut self) {
+        // Best-effort: tell the browser to close the helper page tab.
+        close_helper_page(
+            &self.browser_ws_url,
+            self.host.helper_url(),
+            self.use_hidden_domain,
+        );
+
         self.shutdown.store(true, Ordering::Relaxed);
         if let Some(handle) = self.server_thread.lock().unwrap().take() {
             let _ = handle.join();
@@ -373,6 +380,46 @@ fn bootstrap_helper_page(
     Ok(())
 }
 
+/// Best-effort attempt to close the helper page tab via browser WebSocket.
+/// Silently ignores all errors — this runs during Drop and must not panic.
+fn close_helper_page(browser_ws_url: &str, helper_url: &str, use_hidden_domain: bool) {
+    let close_action = if use_hidden_domain {
+        "sgHideBrowerserClosePage"
+    } else {
+        "sgBrowserClosePage"
+    };
+
+    let result: Result<(), Box<dyn std::error::Error>> = (|| {
+        // Use a raw TcpStream with timeouts instead of tungstenite::connect
+        // which does not expose a connection timeout.
+        let addr = browser_ws_url
+            .trim_start_matches("ws://")
+            .trim_start_matches("wss://");
+        let stream = TcpStream::connect_timeout(
+            &addr.parse().map_err(|e| format!("addr parse: {e}"))?,
+            Duration::from_millis(100),
+        )?;
+        stream.set_read_timeout(Some(Duration::from_millis(200)))?;
+        stream.set_write_timeout(Some(Duration::from_millis(200)))?;
+        let (mut websocket, _) = tungstenite::client(
+            browser_ws_url,
+            stream,
+        )?;
+        websocket.send(Message::Text(
+            r#"{"type":"register","role":"web"}"#.to_string().into(),
+        ))?;
+        // Drain the welcome prelude (best-effort, ignore timeout).
+        let _ = websocket.read();
+        let payload = json!([helper_url, close_action, helper_url]).to_string();
+        websocket.send(Message::Text(payload.into()))?;
+        Ok(())
+    })();
+
+    if let Err(err) = result {
+        eprintln!("close_helper_page best-effort failed (harmless): {err}");
+    }
+}
+
 fn recv_bootstrap_prelude(
     websocket: &mut tungstenite::WebSocket<tungstenite::stream::MaybeTlsStream<TcpStream>>,
 ) -> Result<(), PipeError> {