Prefer v2 websockets if available (#12428)

And also cleanup settings flow to avoid reading many separate flags.

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/tests/suite/client_websockets.rs

@@ -8,6 +8,7 @@ use codex_core::ResponseEvent;
 use codex_core::WireApi;
 use codex_core::X_RESPONSESAPI_INCLUDE_TIMING_METRICS_HEADER;
 use codex_core::features::Feature;
+use codex_core::ws_version_from_features;
 use codex_otel::OtelManager;
 use codex_otel::TelemetryAuthMode;
 use codex_otel::metrics::MetricsClient;
@@ -319,6 +320,62 @@ async fn responses_websocket_v2_requests_use_v2_when_model_prefers_websockets()
     server.shutdown().await;
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn responses_websocket_v2_wins_when_both_features_enabled() {
+    skip_if_no_network!();
+
+    let server = start_websocket_server(vec![vec![
+        vec![
+            ev_response_created("resp-1"),
+            ev_assistant_message("msg-1", "assistant output"),
+            ev_done_with_id("resp-1"),
+        ],
+        vec![ev_response_created("resp-2"), ev_completed("resp-2")],
+    ]])
+    .await;
+
+    let harness = websocket_harness_with_options(&server, false, true, true, false).await;
+    let mut client_session = harness.client.new_session();
+    let prompt_one = prompt_with_input(vec![message_item("hello")]);
+    let prompt_two = prompt_with_input(vec![
+        message_item("hello"),
+        assistant_message_item("msg-1", "assistant output"),
+        message_item("second"),
+    ]);
+
+    stream_until_complete(&mut client_session, &harness, &prompt_one).await;
+    stream_until_complete(&mut client_session, &harness, &prompt_two).await;
+
+    let connection = server.single_connection();
+    assert_eq!(connection.len(), 2);
+    let second = connection.get(1).expect("missing request").body_json();
+    assert_eq!(second["type"].as_str(), Some("response.create"));
+    assert_eq!(second["previous_response_id"].as_str(), Some("resp-1"));
+    assert_eq!(
+        second["input"],
+        serde_json::to_value(&prompt_two.input[2..]).unwrap()
+    );
+
+    let handshake = server.single_handshake();
+    let openai_beta_header = handshake
+        .header(OPENAI_BETA_HEADER)
+        .expect("missing OpenAI-Beta header");
+    assert!(
+        openai_beta_header
+            .split(',')
+            .map(str::trim)
+            .any(|value| value == WS_V2_BETA_HEADER_VALUE)
+    );
+    assert!(
+        !openai_beta_header
+            .split(',')
+            .map(str::trim)
+            .any(|value| value == OPENAI_BETA_RESPONSES_WEBSOCKETS)
+    );
+
+    server.shutdown().await;
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 #[traced_test]
 async fn responses_websocket_emits_websocket_telemetry_events() {
@@ -1251,8 +1308,7 @@ async fn websocket_harness_with_options(
         provider.clone(),
         SessionSource::Exec,
         config.model_verbosity,
-        websocket_enabled,
-        websocket_v2_enabled,
+        ws_version_from_features(&config),
         false,
         runtime_metrics_enabled,
         None,