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/core-skills/src/invocation_utils_tests.rs

@@ -0,0 +1,119 @@
+use super::SkillLoadOutcome;
+use super::SkillMetadata;
+use super::detect_skill_doc_read;
+use super::detect_skill_script_run;
+use super::normalize_path;
+use super::script_run_token;
+use pretty_assertions::assert_eq;
+use std::collections::HashMap;
+use std::path::Path;
+use std::path::PathBuf;
+use std::sync::Arc;
+
+fn test_skill_metadata(skill_doc_path: PathBuf) -> SkillMetadata {
+    SkillMetadata {
+        name: "test-skill".to_string(),
+        description: "test".to_string(),
+        short_description: None,
+        interface: None,
+        dependencies: None,
+        policy: None,
+        permission_profile: None,
+        managed_network_override: None,
+        path_to_skills_md: skill_doc_path,
+        scope: codex_protocol::protocol::SkillScope::User,
+    }
+}
+
+#[test]
+fn script_run_detection_matches_runner_plus_extension() {
+    let tokens = vec![
+        "python3".to_string(),
+        "-u".to_string(),
+        "scripts/fetch_comments.py".to_string(),
+    ];
+
+    assert_eq!(script_run_token(&tokens).is_some(), true);
+}
+
+#[test]
+fn script_run_detection_excludes_python_c() {
+    let tokens = vec![
+        "python3".to_string(),
+        "-c".to_string(),
+        "print(1)".to_string(),
+    ];
+
+    assert_eq!(script_run_token(&tokens).is_some(), false);
+}
+
+#[test]
+fn skill_doc_read_detection_matches_absolute_path() {
+    let skill_doc_path = PathBuf::from("/tmp/skill-test/SKILL.md");
+    let normalized_skill_doc_path = normalize_path(skill_doc_path.as_path());
+    let skill = test_skill_metadata(skill_doc_path);
+    let outcome = SkillLoadOutcome {
+        implicit_skills_by_scripts_dir: Arc::new(HashMap::new()),
+        implicit_skills_by_doc_path: Arc::new(HashMap::from([(normalized_skill_doc_path, skill)])),
+        ..Default::default()
+    };
+
+    let tokens = vec![
+        "cat".to_string(),
+        "/tmp/skill-test/SKILL.md".to_string(),
+        "|".to_string(),
+        "head".to_string(),
+    ];
+    let found = detect_skill_doc_read(&outcome, &tokens, Path::new("/tmp"));
+
+    assert_eq!(
+        found.map(|value| value.name),
+        Some("test-skill".to_string())
+    );
+}
+
+#[test]
+fn skill_script_run_detection_matches_relative_path_from_skill_root() {
+    let skill_doc_path = PathBuf::from("/tmp/skill-test/SKILL.md");
+    let scripts_dir = normalize_path(Path::new("/tmp/skill-test/scripts"));
+    let skill = test_skill_metadata(skill_doc_path);
+    let outcome = SkillLoadOutcome {
+        implicit_skills_by_scripts_dir: Arc::new(HashMap::from([(scripts_dir, skill)])),
+        implicit_skills_by_doc_path: Arc::new(HashMap::new()),
+        ..Default::default()
+    };
+    let tokens = vec![
+        "python3".to_string(),
+        "scripts/fetch_comments.py".to_string(),
+    ];
+
+    let found = detect_skill_script_run(&outcome, &tokens, Path::new("/tmp/skill-test"));
+
+    assert_eq!(
+        found.map(|value| value.name),
+        Some("test-skill".to_string())
+    );
+}
+
+#[test]
+fn skill_script_run_detection_matches_absolute_path_from_any_workdir() {
+    let skill_doc_path = PathBuf::from("/tmp/skill-test/SKILL.md");
+    let scripts_dir = normalize_path(Path::new("/tmp/skill-test/scripts"));
+    let skill = test_skill_metadata(skill_doc_path);
+    let outcome = SkillLoadOutcome {
+        implicit_skills_by_scripts_dir: Arc::new(HashMap::from([(scripts_dir, skill)])),
+        implicit_skills_by_doc_path: Arc::new(HashMap::new()),
+        ..Default::default()
+    };
+    let tokens = vec![
+        "python3".to_string(),
+        "/tmp/skill-test/scripts/fetch_comments.py".to_string(),
+    ];
+
+    let found = detect_skill_script_run(&outcome, &tokens, Path::new("/tmp/other"));
+
+    assert_eq!(
+        found.map(|value| value.name),
+        Some("test-skill".to_string())
+    );
+}