[app-server] Add a method to list experimental features. (#10721)

- [x] Add a method to list experimental features.

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -265,6 +265,10 @@ client_request_definitions! {
         params: v2::ModelListParams,
         response: v2::ModelListResponse,
     },
+    ExperimentalFeatureList => "experimentalFeature/list" {
+        params: v2::ExperimentalFeatureListParams,
+        response: v2::ExperimentalFeatureListResponse,
+    },
     #[experimental("collaborationMode/list")]
     /// Lists collaboration mode presets.
     CollaborationModeList => "collaborationMode/list" {
@@ -1087,6 +1091,26 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn serialize_list_experimental_features() -> Result<()> {
+        let request = ClientRequest::ExperimentalFeatureList {
+            request_id: RequestId::Integer(8),
+            params: v2::ExperimentalFeatureListParams::default(),
+        };
+        assert_eq!(
+            json!({
+                "method": "experimentalFeature/list",
+                "id": 8,
+                "params": {
+                    "cursor": null,
+                    "limit": null
+                }
+            }),
+            serde_json::to_value(&request)?,
+        );
+        Ok(())
+    }
+
     #[test]
     fn mock_experimental_method_is_marked_experimental() {
         let request = ClientRequest::MockExperimentalMethod {