Add realtime voice selection (#17176)

- Add realtime voice selection for realtime/start.
- Expose the supported v1/v2 voice lists and cover explicit, configured,
default, and invalid voice paths.

codex-rs/app-server/tests/common/mcp_process.rs

@@ -67,6 +67,7 @@ use codex_app_server_protocol::ThreadMetadataUpdateParams;
 use codex_app_server_protocol::ThreadReadParams;
 use codex_app_server_protocol::ThreadRealtimeAppendAudioParams;
 use codex_app_server_protocol::ThreadRealtimeAppendTextParams;
+use codex_app_server_protocol::ThreadRealtimeListVoicesParams;
 use codex_app_server_protocol::ThreadRealtimeStartParams;
 use codex_app_server_protocol::ThreadRealtimeStopParams;
 use codex_app_server_protocol::ThreadResumeParams;
@@ -664,6 +665,15 @@ impl McpProcess {
         self.send_request("thread/realtime/stop", params).await
     }
 
+    pub async fn send_thread_realtime_list_voices_request(
+        &mut self,
+        params: ThreadRealtimeListVoicesParams,
+    ) -> anyhow::Result<i64> {
+        let params = Some(serde_json::to_value(params)?);
+        self.send_request("thread/realtime/listVoices", params)
+            .await
+    }
+
     /// Deterministically clean up an intentionally in-flight turn.
     ///
     /// Some tests assert behavior while a turn is still running. Returning from those tests