fix: update OutgoingMessageSender::send_response() to take Serialize (#2263)

This makes `send_response()` easier to work with.

codex-rs/mcp-server/src/outgoing_message.rs

@@ -18,6 +18,8 @@ use tokio::sync::mpsc;
 use tokio::sync::oneshot;
 use tracing::warn;
 
+use crate::error_code::INTERNAL_ERROR_CODE;
+
 /// Sends messages to the client and manages request callbacks.
 pub(crate) struct OutgoingMessageSender {
     next_request_id: AtomicI64,
@@ -74,9 +76,24 @@ impl OutgoingMessageSender {
         }
     }
 
-    pub(crate) async fn send_response(&self, id: RequestId, result: Result) {
-        let outgoing_message = OutgoingMessage::Response(OutgoingResponse { id, result });
-        let _ = self.sender.send(outgoing_message).await;
+    pub(crate) async fn send_response<T: Serialize>(&self, id: RequestId, response: T) {
+        match serde_json::to_value(response) {
+            Ok(result) => {
+                let outgoing_message = OutgoingMessage::Response(OutgoingResponse { id, result });
+                let _ = self.sender.send(outgoing_message).await;
+            }
+            Err(err) => {
+                self.send_error(
+                    id,
+                    JSONRPCErrorError {
+                        code: INTERNAL_ERROR_CODE,
+                        message: format!("failed to serialize response: {err}"),
+                        data: None,
+                    },
+                )
+                .await;
+            }
+        }
     }
 
     pub(crate) async fn send_event_as_notification(