Add configurable gating for the sleep tool (#41243)

## What changed

- Add a stable `sleep_tool` feature that can enable or disable registration of the built-in sleep tool independently of the clock tool.
- Support structured `features.sleep_tool` configuration with `model_driven` and `always_on` modes. The default `model_driven` mode preserves the existing model and `current_time_reminder` behavior, while `always_on` registers sleep whenever the feature is enabled.
- Preserve nested sleep-tool configuration across CLI overrides, config merges, and feature toggles, and expose the settings in the generated config schema.

## Testing

- Cover feature-map overrides, both selection modes, legacy clock settings, config merging and editing, and invalid mode rejection.

GitOrigin-RevId: 18eadc582f8a4445958c29d063e5be495276703e

codex-rs/core/src/config/edit_tests.rs

@@ -136,6 +136,33 @@ fn multi_agent_v2_feature_toggle_preserves_nested_configuration() {
     );
 }
 
+#[test]
+fn sleep_tool_feature_toggle_preserves_mode() {
+    let tmp = tempdir().expect("tmpdir");
+    let codex_home = tmp.path();
+    let config_path = codex_home.join(CONFIG_TOML_FILE);
+    std::fs::write(
+        &config_path,
+        "[features.sleep_tool]\nmode = \"always_on\"\n",
+    )
+    .expect("write config");
+
+    for enabled in [false, true] {
+        ConfigEditsBuilder::new(codex_home)
+            .set_feature_enabled("sleep_tool", enabled)
+            .apply_blocking()
+            .expect("toggle feature");
+        let actual: TomlValue =
+            toml::from_str(&std::fs::read_to_string(&config_path).expect("read config"))
+                .expect("parse config");
+        let expected: TomlValue = toml::from_str(&format!(
+            "[features.sleep_tool]\nenabled = {enabled}\nmode = \"always_on\"\n",
+        ))
+        .expect("parse expected config");
+        assert_eq!(actual, expected);
+    }
+}
+
 #[test]
 fn network_proxy_feature_toggle_preserves_credential_broker_configuration() {
     let tmp = tempdir().expect("tmpdir");

codex-rs/core/src/config/mod.rs

@@ -73,6 +73,7 @@ use codex_features::Features;
 use codex_features::FeaturesToml;
 use codex_features::MultiAgentV2ConfigToml;
 use codex_features::NetworkProxyConfigToml;
+use codex_features::SleepToolMode;
 use codex_features::TokenBudgetConfigToml;
 use codex_git_utils::resolve_root_git_project_for_trust;
 use codex_http_client::HttpClientFactory;
@@ -1045,6 +1046,8 @@ pub struct Config {
     pub rollout_budget: Option<RolloutBudgetConfig>,
     /// Current-time reminder and clock tool configuration, when enabled.
     pub current_time_reminder: Option<CurrentTimeReminderConfig>,
+    /// How the sleep tool is selected when its feature gate is enabled.
+    pub sleep_tool_mode: SleepToolMode,
 
     /// Centralized feature flags; source of truth for feature gating.
     pub features: ManagedFeatures,
@@ -3684,6 +3687,15 @@ impl Config {
         let token_budget = resolve_token_budget_config(&cfg, &features)?;
         let rollout_budget = resolve_rollout_budget_config(&cfg, &features)?;
         let current_time_reminder = resolve_current_time_reminder_config(&cfg, &features)?;
+        let sleep_tool_mode = cfg
+            .features
+            .as_ref()
+            .and_then(|features| features.sleep_tool.as_ref())
+            .and_then(|feature| match feature {
+                FeatureToml::Enabled(_) => None,
+                FeatureToml::Config(config) => config.mode,
+            })
+            .unwrap_or_default();
         let terminal_resize_reflow = resolve_terminal_resize_reflow_config(&cfg);
 
         let agent_roles =
@@ -4282,6 +4294,7 @@ impl Config {
             token_budget,
             rollout_budget,
             current_time_reminder,
+            sleep_tool_mode,
             features,
             suppress_unstable_features_warning: cfg
                 .suppress_unstable_features_warning