MCP batch runs as one request in the app (#743) (#885)

The app's control protocol gets engine.batch: the steps run in one request (so one frame), each as engine.execute runs it, stopping at the first failure and rolling back to the checkpoint by default. The MCP batch tool sends it to a running app (with the control token), is never resent after a lost reply, and falls back to step-by-step when the app refuses (agent cursor shown, or a step loads a file). A batch may take up to an hour to answer.

apps/solidcraft/src/control_server.rs

@@ -156,12 +156,14 @@ fn serve(stream: TcpStream, token: &str, tx: Sender<ControlRequest>, ctx: egui::
                 let id = msg.get("id").cloned().unwrap_or(Value::Null);
                 let method = msg.get("method").and_then(Value::as_str).unwrap_or("").to_string();
                 let params = msg.get("params").cloned().unwrap_or(json!({}));
+                // A batch replaces many short requests: the whole of it may take long (#743).
+                let wait = Duration::from_secs(if method == "engine.batch" { 3600 } else { 60 });
                 let (req, rrx) = ControlRequest::new(method, params);
                 if tx.send(req).is_err() {
                     break;
                 }
                 ctx.request_repaint();
-                let mut r = rrx.recv_timeout(Duration::from_secs(60)).unwrap_or_else(|_| json!({"ok": false, "error": "timeout"}));
+                let mut r = rrx.recv_timeout(wait).unwrap_or_else(|_| json!({"ok": false, "error": "timeout"}));
                 if let Some(o) = r.as_object_mut() {
                     o.insert("id".into(), id);
                 }