jsonrpc: Specify mandatory jsonrpc Version Property

rust/rpc.rs

@@ -158,7 +158,7 @@ where
                 message = outgoing_rx.next() => {
                     if let Some(message) = message {
                         outgoing_line.clear();
-                        serde_json::to_writer(&mut outgoing_line, &message).map_err(Error::into_internal_error)?;
+                        serde_json::to_writer(&mut outgoing_line, &JsonRpcMessage::wrap(&message)).map_err(Error::into_internal_error)?;
                         log::trace!("send: {}", String::from_utf8_lossy(&outgoing_line));
                         outgoing_line.push(b'\n');
                         outgoing_bytes.write_all(&outgoing_line).await.ok();
@@ -190,7 +190,7 @@ where
                                                 result: ResponseResult::Error(err),
                                             };
 
-                                            serde_json::to_writer(&mut outgoing_line, &error_response)?;
+                                            serde_json::to_writer(&mut outgoing_line, &JsonRpcMessage::wrap(&error_response))?;
                                             log::trace!("send: {}", String::from_utf8_lossy(&outgoing_line));
                                             outgoing_line.push(b'\n');
                                             outgoing_bytes.write_all(&outgoing_line).await.ok();
@@ -325,6 +325,34 @@ pub enum OutgoingMessage<Local: Side, Remote: Side> {
     },
 }
 
+/// Either [`OutgoingMessage`] or [`IncomingMessage`] with `"jsonrpc": "2.0"` specified as
+/// [required by JSON-RPC 2.0 Specification][1].
+///
+/// [1]: https://www.jsonrpc.org/specification#compatibility
+#[derive(Debug, Serialize, Deserialize)]
+pub struct JsonRpcMessage<M> {
+    jsonrpc: &'static str,
+    #[serde(flatten)]
+    message: M,
+}
+
+impl<M> JsonRpcMessage<M> {
+    /// Used version of [JSON-RPC protocol].
+    ///
+    /// [JSON-RPC]: https://www.jsonrpc.org
+    pub const VERSION: &'static str = "2.0";
+
+    /// Wraps the provided [`OutgoingMessage`] or [`IncomingMessage`] into a versioned
+    /// [`JsonRpcMessage`].
+    #[must_use]
+    pub fn wrap(message: M) -> Self {
+        Self {
+            jsonrpc: Self::VERSION,
+            message,
+        }
+    }
+}
+
 #[derive(Debug, Serialize, Deserialize, Clone)]
 #[serde(rename_all = "snake_case")]
 pub enum ResponseResult<Res> {

rust/rpc_tests.rs

@@ -612,49 +612,54 @@ async fn test_full_conversation_flow() {
 async fn test_notification_wire_format() {
     use crate::{
         AgentNotification, AgentSide, CancelNotification, ClientNotification, ClientSide,
-        ContentBlock, SessionNotification, SessionUpdate, TextContent, rpc::OutgoingMessage,
+        ContentBlock, SessionNotification, SessionUpdate, TextContent,
+        rpc::{JsonRpcMessage, OutgoingMessage},
     };
     use serde_json::{Value, json};
 
     // Test client -> agent notification wire format
-    let outgoing_msg = OutgoingMessage::<ClientSide, AgentSide>::Notification {
-        method: "cancel",
-        params: Some(ClientNotification::CancelNotification(CancelNotification {
-            session_id: SessionId("test-123".into()),
-        })),
-    };
+    let outgoing_msg =
+        JsonRpcMessage::wrap(OutgoingMessage::<ClientSide, AgentSide>::Notification {
+            method: "cancel",
+            params: Some(ClientNotification::CancelNotification(CancelNotification {
+                session_id: SessionId("test-123".into()),
+            })),
+        });
 
     let serialized: Value = serde_json::to_value(&outgoing_msg).unwrap();
     assert_eq!(
         serialized,
         json!({
+            "jsonrpc": "2.0",
             "method": "cancel",
             "params": {
                 "sessionId": "test-123"
-            }
+            },
         })
     );
 
     // Test agent -> client notification wire format
-    let outgoing_msg = OutgoingMessage::<AgentSide, ClientSide>::Notification {
-        method: "sessionUpdate",
-        params: Some(AgentNotification::SessionNotification(
-            SessionNotification {
-                session_id: SessionId("test-456".into()),
-                update: SessionUpdate::AgentMessageChunk {
-                    content: ContentBlock::Text(TextContent {
-                        annotations: None,
-                        text: "Hello".to_string(),
-                    }),
+    let outgoing_msg =
+        JsonRpcMessage::wrap(OutgoingMessage::<AgentSide, ClientSide>::Notification {
+            method: "sessionUpdate",
+            params: Some(AgentNotification::SessionNotification(
+                SessionNotification {
+                    session_id: SessionId("test-456".into()),
+                    update: SessionUpdate::AgentMessageChunk {
+                        content: ContentBlock::Text(TextContent {
+                            annotations: None,
+                            text: "Hello".to_string(),
+                        }),
+                    },
                 },
-            },
-        )),
-    };
+            )),
+        });
 
     let serialized: Value = serde_json::to_value(&outgoing_msg).unwrap();
     assert_eq!(
         serialized,
         json!({
+            "jsonrpc": "2.0",
             "method": "sessionUpdate",
             "params": {
                 "sessionId": "test-456",