Gate content item kinds behind a feature flag (#40450)

## What changed

- Add the under-development `content_item_kinds` feature, disabled by default.
- Strip content item classifications from Responses input when the feature is
  disabled while preserving other passthrough metadata.

## Testing

- Add coverage that disables the feature and verifies requests omit content item
  kinds without removing the turn ID.

GitOrigin-RevId: f938feb2895d766d979b1666fc7b97fd128fe8a7

codex-rs/core/tests/common/test_codex.rs

@@ -1339,6 +1339,10 @@ pub fn test_codex() -> TestCodexBuilder {
                 .features
                 .disable(Feature::ShellSnapshot)
                 .expect("test config should allow ShellSnapshot override");
+            config
+                .features
+                .enable(Feature::ContentItemKinds)
+                .expect("test config should allow ContentItemKinds override");
         })],
         auth: CodexAuth::from_api_key("dummy"),
         pre_build_hooks: vec![],

codex-rs/core/tests/responses_headers.rs

@@ -4,6 +4,7 @@ use std::sync::Arc;
 use codex_core::ModelClient;
 use codex_core::Prompt;
 use codex_core::ResponseEvent;
+use codex_features::Feature;
 use codex_login::CodexAuth;
 use codex_login::auth::AgentIdentityAuthPolicy;
 use codex_model_provider_info::ModelProviderInfo;
@@ -128,6 +129,7 @@ async fn responses_stream_includes_subagent_header_on_review() {
         session_source.clone(),
         "test_originator".to_string(),
         config.model_verbosity,
+        config.features.enabled(Feature::ContentItemKinds),
         /*enable_request_compression*/ false,
         /*include_timing_metrics*/ false,
         /*beta_features_header*/ None,
@@ -264,6 +266,7 @@ async fn responses_stream_includes_subagent_header_on_other() {
         session_source.clone(),
         "test_originator".to_string(),
         config.model_verbosity,
+        config.features.enabled(Feature::ContentItemKinds),
         /*enable_request_compression*/ false,
         /*include_timing_metrics*/ false,
         /*beta_features_header*/ None,
@@ -385,6 +388,7 @@ async fn responses_respects_model_info_overrides_from_config() {
         session_source.clone(),
         "test_originator".to_string(),
         config.model_verbosity,
+        config.features.enabled(Feature::ContentItemKinds),
         /*enable_request_compression*/ false,
         /*include_timing_metrics*/ false,
         /*beta_features_header*/ None,

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

@@ -1375,6 +1375,10 @@ async fn fork_injects_changed_agents_md_once() -> Result<()> {
     fork_config.model_provider = parent.config.model_provider.clone();
     fork_config.model_catalog = parent.config.model_catalog.clone();
     fork_config.codex_self_exe = parent.config.codex_self_exe.clone();
+    fork_config
+        .features
+        .enable(Feature::ContentItemKinds)
+        .expect("test config should allow ContentItemKinds override");
     let forked = parent
         .thread_manager
         .fork_thread(

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

@@ -1524,6 +1524,7 @@ async fn send_request_with_provider(provider: ModelProviderInfo) {
         SessionSource::Exec,
         "test_originator".to_string(),
         config.model_verbosity,
+        config.features.enabled(Feature::ContentItemKinds),
         /*enable_request_compression*/ false,
         /*include_timing_metrics*/ false,
         /*beta_features_header*/ None,
@@ -3009,6 +3010,7 @@ async fn azure_responses_request_does_not_store_and_preserves_prefixed_item_ids(
         SessionSource::Exec,
         "test_originator".to_string(),
         config.model_verbosity,
+        config.features.enabled(Feature::ContentItemKinds),
         /*enable_request_compression*/ false,
         /*include_timing_metrics*/ false,
         /*beta_features_header*/ None,

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

@@ -2514,6 +2514,7 @@ async fn websocket_harness_with_provider_options_and_auth(
         SessionSource::Exec,
         "test_originator".to_string(),
         config.model_verbosity,
+        config.features.enabled(Feature::ContentItemKinds),
         /*enable_request_compression*/ false,
         runtime_metrics_enabled,
         /*beta_features_header*/ None,

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

@@ -215,3 +215,39 @@ async fn first_request_item_types_roles_and_content_annotations() -> Result<()>
 
     Ok(())
 }
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn content_item_kinds_are_omitted_when_feature_disabled() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = start_mock_server().await;
+    let response = mount_sse_once(
+        &server,
+        sse(vec![ev_response_created("resp-1"), ev_completed("resp-1")]),
+    )
+    .await;
+    let test = test_codex()
+        .with_config(|config| {
+            config.developer_instructions = Some("Keep other metadata intact.".into());
+            config
+                .features
+                .disable(Feature::ContentItemKinds)
+                .expect("test config should allow ContentItemKinds override");
+        })
+        .build_with_auto_env(&server)
+        .await?;
+
+    test.submit_text_turn("inspect request metadata").await?;
+
+    let input = response.single_request().input();
+    assert!(input.iter().all(|item| {
+        item.pointer("/internal_chat_message_metadata_passthrough/content_item_kinds")
+            .is_none()
+    }));
+    assert!(input.iter().any(|item| {
+        item.pointer("/internal_chat_message_metadata_passthrough/turn_id")
+            .is_some()
+    }));
+
+    Ok(())
+}