Reduce app-server JSON serialization overhead (#34761)

## What changed

- Decode `JSONRPCRequest` into `ClientRequest` without serializing the entire request back into an intermediate JSON value.
- Define every client method's wire name explicitly and use it directly for request, response, and tracing method lookups.
- Serialize outgoing transport messages directly to JSON strings instead of first building a `serde_json::Value`.

## Testing

- Add regression coverage that compares direct request conversion with Serde decoding, including omitted and null parameters, legacy methods, and unknown methods.
- Verify that direct outgoing-message serialization preserves the notification wire shape.

GitOrigin-RevId: 304e14bcaea24e32743bf852a60a208e2f273db3

codex-rs/app-server-transport/src/transport/mod.rs

@@ -256,14 +256,7 @@ async fn enqueue_incoming_message(
 }
 
 fn serialize_outgoing_message(outgoing_message: OutgoingMessage) -> Option<String> {
-    let value = match serde_json::to_value(outgoing_message) {
-        Ok(value) => value,
-        Err(err) => {
-            error!("Failed to convert OutgoingMessage to JSON value: {err}");
-            return None;
-        }
-    };
-    match serde_json::to_string(&value) {
+    match serde_json::to_string(&outgoing_message) {
         Ok(json) => Some(json),
         Err(err) => {
             error!("Failed to serialize JSONRPCMessage: {err}");
@@ -295,6 +288,32 @@ mod tests {
         );
     }
 
+    #[test]
+    fn serialize_outgoing_message_preserves_wire_shape() {
+        let message = OutgoingMessage::AppServerNotification(ServerNotificationEnvelope {
+            notification: ServerNotification::ConfigWarning(ConfigWarningNotification {
+                summary: "summary".to_string(),
+                details: None,
+                path: None,
+                range: None,
+            }),
+            emitted_at_ms: Some(1_234),
+        });
+
+        let json = serialize_outgoing_message(message).expect("message should serialize");
+        assert_eq!(
+            serde_json::from_str::<serde_json::Value>(&json).expect("message should be valid JSON"),
+            json!({
+                "method": "configWarning",
+                "params": {
+                    "summary": "summary",
+                    "details": null,
+                },
+                "emittedAtMs": 1_234,
+            })
+        );
+    }
+
     #[tokio::test]
     async fn enqueue_incoming_request_returns_overload_error_when_queue_is_full() {
         let connection_id = ConnectionId(42);