Extract codex-core-skills crate (#15749)

## Summary
- move skill loading and management into codex-core-skills
- leave codex-core with the thin integration layer and shared wiring

## Testing
- CI

---------

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

codex-rs/config/src/lib.rs

@@ -5,7 +5,9 @@ mod diagnostics;
 mod fingerprint;
 mod merge;
 mod overrides;
+mod project_root_markers;
 mod requirements_exec_policy;
+mod skills_config;
 mod state;
 
 pub const CONFIG_TOML_FILE: &str = "config.toml";
@@ -46,12 +48,17 @@ pub use diagnostics::io_error_from_config_error;
 pub use fingerprint::version_for_toml;
 pub use merge::merge_toml_values;
 pub use overrides::build_cli_overrides_layer;
+pub use project_root_markers::default_project_root_markers;
+pub use project_root_markers::project_root_markers_from_config;
 pub use requirements_exec_policy::RequirementsExecPolicy;
 pub use requirements_exec_policy::RequirementsExecPolicyDecisionToml;
 pub use requirements_exec_policy::RequirementsExecPolicyParseError;
 pub use requirements_exec_policy::RequirementsExecPolicyPatternTokenToml;
 pub use requirements_exec_policy::RequirementsExecPolicyPrefixRuleToml;
 pub use requirements_exec_policy::RequirementsExecPolicyToml;
+pub use skills_config::BundledSkillsConfig;
+pub use skills_config::SkillConfig;
+pub use skills_config::SkillsConfig;
 pub use state::ConfigLayerEntry;
 pub use state::ConfigLayerStack;
 pub use state::ConfigLayerStackOrdering;

codex-rs/config/src/project_root_markers.rs

@@ -0,0 +1,50 @@
+use std::io;
+
+use toml::Value as TomlValue;
+
+const DEFAULT_PROJECT_ROOT_MARKERS: &[&str] = &[".git"];
+
+/// Reads `project_root_markers` from a merged `config.toml` [toml::Value].
+///
+/// Invariants:
+/// - If `project_root_markers` is not specified, returns `Ok(None)`.
+/// - If `project_root_markers` is specified, returns `Ok(Some(markers))` where
+///   `markers` is a `Vec<String>` (including `Ok(Some(Vec::new()))` for an
+///   empty array, which indicates that root detection should be disabled).
+/// - Returns an error if `project_root_markers` is specified but is not an
+///   array of strings.
+pub fn project_root_markers_from_config(config: &TomlValue) -> io::Result<Option<Vec<String>>> {
+    let Some(table) = config.as_table() else {
+        return Ok(None);
+    };
+    let Some(markers_value) = table.get("project_root_markers") else {
+        return Ok(None);
+    };
+    let TomlValue::Array(entries) = markers_value else {
+        return Err(io::Error::new(
+            io::ErrorKind::InvalidData,
+            "project_root_markers must be an array of strings",
+        ));
+    };
+    if entries.is_empty() {
+        return Ok(Some(Vec::new()));
+    }
+    let mut markers = Vec::new();
+    for entry in entries {
+        let Some(marker) = entry.as_str() else {
+            return Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                "project_root_markers must be an array of strings",
+            ));
+        };
+        markers.push(marker.to_string());
+    }
+    Ok(Some(markers))
+}
+
+pub fn default_project_root_markers() -> Vec<String> {
+    DEFAULT_PROJECT_ROOT_MARKERS
+        .iter()
+        .map(ToString::to_string)
+        .collect()
+}

codex-rs/config/src/skills_config.rs

@@ -0,0 +1,53 @@
+//! Skill-related configuration types shared across crates.
+
+use codex_utils_absolute_path::AbsolutePathBuf;
+use schemars::JsonSchema;
+use serde::Deserialize;
+use serde::Serialize;
+
+const fn default_enabled() -> bool {
+    true
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema)]
+#[schemars(deny_unknown_fields)]
+pub struct SkillConfig {
+    /// Path-based selector.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub path: Option<AbsolutePathBuf>,
+    /// Name-based selector.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub name: Option<String>,
+    pub enabled: bool,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, Default, PartialEq, Eq, JsonSchema)]
+#[schemars(deny_unknown_fields)]
+pub struct SkillsConfig {
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub bundled: Option<BundledSkillsConfig>,
+
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub config: Vec<SkillConfig>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema)]
+#[schemars(deny_unknown_fields)]
+pub struct BundledSkillsConfig {
+    #[serde(default = "default_enabled")]
+    pub enabled: bool,
+}
+
+impl Default for BundledSkillsConfig {
+    fn default() -> Self {
+        Self { enabled: true }
+    }
+}
+
+impl TryFrom<toml::Value> for SkillsConfig {
+    type Error = toml::de::Error;
+
+    fn try_from(value: toml::Value) -> Result<Self, Self::Error> {
+        SkillsConfig::deserialize(value)
+    }
+}