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/config/src/merge.rs

@@ -67,7 +67,10 @@ pub fn is_structured_feature_path<S: AsRef<str>>(path: &[S]) -> bool {
     };
 
     features.as_ref() == "features"
-        && matches!(feature.as_ref(), "multi_agent_v2" | "network_proxy")
+        && matches!(
+            feature.as_ref(),
+            "multi_agent_v2" | "network_proxy" | "sleep_tool"
+        )
 }
 
 fn merge_toml_values_at_path(base: &mut TomlValue, overlay: &TomlValue, path: &mut Vec<String>) {

codex-rs/config/src/merge_tests.rs

@@ -255,6 +255,38 @@ fn multi_agent_v2_cli_overrides_preserve_boolean_and_nested_configuration() {
     }
 }
 
+#[test]
+fn sleep_tool_overrides_preserve_disabled_state_and_mode() {
+    for feature_path in ["features", "profiles.work.features"] {
+        let disabled = (
+            format!("{feature_path}.sleep_tool"),
+            TomlValue::Boolean(false),
+        );
+        let mode = (
+            format!("{feature_path}.sleep_tool.mode"),
+            TomlValue::String("always_on".to_string()),
+        );
+        let expected = parse_toml(&format!(
+            "[{feature_path}.sleep_tool]\nenabled = false\nmode = \"always_on\"\n",
+        ));
+        for overrides in [vec![disabled.clone(), mode.clone()], vec![mode, disabled]] {
+            assert_eq!(crate::build_cli_overrides_layer(&overrides), expected);
+        }
+
+        let boolean_layer = parse_toml(&format!("[{feature_path}]\nsleep_tool = false\n"));
+        let table_layer = parse_toml(&format!(
+            "[{feature_path}.sleep_tool]\nmode = \"always_on\"\n",
+        ));
+        for (mut base, overlay) in [
+            (boolean_layer.clone(), table_layer.clone()),
+            (table_layer, boolean_layer),
+        ] {
+            merge_toml_values(&mut base, &overlay);
+            assert_eq!(base, expected);
+        }
+    }
+}
+
 #[test]
 fn network_proxy_feature_overrides_preserve_credential_broker_configuration() {
     let enabled = (

codex-rs/config/src/schema.rs

@@ -122,6 +122,15 @@ pub fn features_schema(schema_gen: &mut SchemaGenerator) -> Schema {
             );
             continue;
         }
+        if feature.id == codex_features::Feature::SleepTool {
+            validation.properties.insert(
+                feature.key.to_string(),
+                schema_gen.subschema_for::<codex_features::FeatureToml<
+                    codex_features::SleepToolConfigToml,
+                >>(),
+            );
+            continue;
+        }
         if feature.id == codex_features::Feature::AppsMcpPathOverride {
             validation.properties.insert(
                 feature.key.to_string(),