[00286] Fix widget_harness missing initial build in WebSocket handler

Add runtime.build().await before current_tree() check in handle_socket
so the initial refresh message is sent to WebSocket clients. Also add a
unit test verifying build() populates the tree.

Author: rorychatt

rusty/src/core/runtime.rs

@@ -234,6 +234,14 @@ mod tests {
         assert!(json.to_string().contains("Hello from runtime"));
     }
 
+    #[tokio::test]
+    async fn test_runtime_build_populates_tree() {
+        let mut runtime = Runtime::new(TestView);
+        assert!(runtime.current_tree().await.is_none());
+        runtime.build().await;
+        assert!(runtime.current_tree().await.is_some());
+    }
+
     #[tokio::test]
     async fn test_runtime_build_assigns_ids_automatically() {
         use crate::widgets::layout::Layout;

rusty/src/server/ws.rs

@@ -159,6 +159,7 @@ async fn handle_socket(socket: WebSocket, state: Arc<AppState>) {
     // Send initial render from this session's own runtime
     {
         let mut session = session_arc.write().await;
+        session.runtime.build().await;
         if let Some(tree) = session.runtime.current_tree().await {
             let msg = ServerMessage::Refresh {
                 widgets: tree.clone(),