Update ToolSearch to be enabled by default (#17854)

## Summary
- Promote `Feature::ToolSearch` to `Stable` and enable it in the default
feature set
- Update feature tests and tool registry coverage to match the new
default
- Adjust the search-tool integration test to assert the default-on path
and explicit disable fallback

## Testing
- `just fmt`
- `cargo test -p codex-features`
- `cargo test -p codex-core --test all search_tool`
- `cargo test -p codex-tools`

Author: mzeng-openai

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

@@ -93,7 +93,7 @@ fn tool_search_output_tools(request: &ResponsesRequest, call_id: &str) -> Vec<Va
         .unwrap_or_default()
 }
 
-fn configure_apps_without_tool_search(config: &mut Config, apps_base_url: &str) {
+fn configure_search_capable_apps(config: &mut Config, apps_base_url: &str) {
     config
         .features
         .enable(Feature::Apps)
@@ -112,22 +112,26 @@ fn configure_apps_without_tool_search(config: &mut Config, apps_base_url: &str)
     config.model_catalog = Some(model_catalog);
 }
 
-fn configure_apps(config: &mut Config, apps_base_url: &str) {
-    configure_apps_without_tool_search(config, apps_base_url);
+fn configure_apps_without_tool_search(config: &mut Config, apps_base_url: &str) {
+    configure_search_capable_apps(config, apps_base_url);
     config
         .features
-        .enable(Feature::ToolSearch)
+        .disable(Feature::ToolSearch)
         .expect("test config should allow feature update");
 }
 
+fn configure_apps(config: &mut Config, apps_base_url: &str) {
+    configure_search_capable_apps(config, apps_base_url);
+}
+
 fn configured_builder(apps_base_url: String) -> TestCodexBuilder {
     test_codex()
         .with_auth(CodexAuth::create_dummy_chatgpt_auth_for_testing())
         .with_config(move |config| configure_apps(config, apps_base_url.as_str()))
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn search_tool_flag_adds_tool_search() -> Result<()> {
+async fn search_tool_enabled_by_default_adds_tool_search() -> Result<()> {
     skip_if_no_network!(Ok(()));
 
     let server = start_mock_server().await;
@@ -185,7 +189,7 @@ async fn search_tool_flag_adds_tool_search() -> Result<()> {
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn tool_search_disabled_by_default_exposes_apps_tools_directly() -> Result<()> {
+async fn tool_search_disabled_exposes_apps_tools_directly() -> Result<()> {
     skip_if_no_network!(Ok(()));
 
     let server = start_mock_server().await;

codex-rs/features/src/lib.rs

@@ -788,8 +788,8 @@ pub const FEATURES: &[FeatureSpec] = &[
     FeatureSpec {
         id: Feature::ToolSearch,
         key: "tool_search",
-        stage: Stage::UnderDevelopment,
-        default_enabled: false,
+        stage: Stage::Stable,
+        default_enabled: true,
     },
     FeatureSpec {
         id: Feature::UnavailableDummyTools,

codex-rs/features/src/tests.rs

@@ -128,9 +128,9 @@ fn tool_suggest_is_stable_and_enabled_by_default() {
 }
 
 #[test]
-fn tool_search_is_under_development_and_disabled_by_default() {
-    assert_eq!(Feature::ToolSearch.stage(), Stage::UnderDevelopment);
-    assert_eq!(Feature::ToolSearch.default_enabled(), false);
+fn tool_search_is_stable_and_enabled_by_default() {
+    assert_eq!(Feature::ToolSearch.stage(), Stage::Stable);
+    assert_eq!(Feature::ToolSearch.default_enabled(), true);
 }
 
 #[test]

codex-rs/tools/src/tool_registry_plan_tests.rs

@@ -1334,7 +1334,7 @@ fn search_tool_description_lists_each_mcp_source_once() {
 }
 
 #[test]
-fn search_tool_requires_model_capability_and_feature_flag() {
+fn search_tool_requires_model_capability_and_enabled_feature() {
     let model_info = search_capable_model_info();
     let deferred_mcp_tools = Some(vec![deferred_mcp_tool(
         "_create_event",
@@ -1367,10 +1367,12 @@ fn search_tool_requires_model_capability_and_feature_flag() {
     );
     assert_lacks_tool_name(&tools, TOOL_SEARCH_TOOL_NAME);
 
+    let mut features_without_tool_search = Features::with_defaults();
+    features_without_tool_search.disable(Feature::ToolSearch);
     let tools_config = ToolsConfig::new(&ToolsConfigParams {
         model_info: &model_info,
         available_models: &available_models,
-        features: &features,
+        features: &features_without_tool_search,
         image_generation_tool_auth_allowed: true,
         web_search_mode: Some(WebSearchMode::Cached),
         session_source: SessionSource::Cli,
@@ -1385,8 +1387,6 @@ fn search_tool_requires_model_capability_and_feature_flag() {
     );
     assert_lacks_tool_name(&tools, TOOL_SEARCH_TOOL_NAME);
 
-    let mut features = Features::with_defaults();
-    features.enable(Feature::ToolSearch);
     let tools_config = ToolsConfig::new(&ToolsConfigParams {
         model_info: &model_info,
         available_models: &available_models,