fix: use macros to ensure request/response symmetry (#4529)

Manually curating `protocol-ts/src/lib.rs` was error-prone, as expected.
I finally asked Codex to write some Rust macros so we can ensure that:

- For every variant of `ClientRequest` and `ServerRequest`, there is an
associated `params` and `response` type.
- All response types are included automatically in the output of `codex
generate-ts`.

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

@@ -3,6 +3,7 @@ use std::sync::atomic::AtomicI64;
 use std::sync::atomic::Ordering;
 
 use codex_protocol::mcp_protocol::ServerNotification;
+use codex_protocol::mcp_protocol::ServerRequestPayload;
 use mcp_types::JSONRPC_VERSION;
 use mcp_types::JSONRPCError;
 use mcp_types::JSONRPCErrorError;
@@ -38,8 +39,7 @@ impl OutgoingMessageSender {
 
     pub(crate) async fn send_request(
         &self,
-        method: &str,
-        params: Option<serde_json::Value>,
+        request: ServerRequestPayload,
     ) -> oneshot::Receiver<Result> {
         let id = RequestId::Integer(self.next_request_id.fetch_add(1, Ordering::Relaxed));
         let outgoing_message_id = id.clone();
@@ -49,6 +49,14 @@ impl OutgoingMessageSender {
             request_id_to_callback.insert(id, tx_approve);
         }
 
+        let method = request.method();
+        let params_value = request.into_params_value();
+        let params = if params_value.is_null() {
+            None
+        } else {
+            Some(params_value)
+        };
+
         let outgoing_message = OutgoingMessage::Request(OutgoingRequest {
             id: outgoing_message_id,
             method: method.to_string(),