Reimplement skills loading using SkillsManager + skills/list op. (#7914)

refactor the way we load and manage skills:
1. Move skill discovery/caching into SkillsManager and reuse it across
sessions.
2. Add the skills/list API (Op::ListSkills/SkillsListResponse) to fetch
skills for one or more cwds. Also update app-server for VSCE/App;
3. Trigger skills/list during session startup so UIs preload skills and
handle errors immediately.

codex-rs/core/src/auth.rs

@@ -64,6 +64,7 @@ const REFRESH_TOKEN_UNKNOWN_MESSAGE: &str =
 const REFRESH_TOKEN_URL: &str = "https://auth.openai.com/oauth/token";
 pub const REFRESH_TOKEN_URL_OVERRIDE_ENV_VAR: &str = "CODEX_REFRESH_TOKEN_URL_OVERRIDE";
 
+#[cfg(any(test, feature = "test-support"))]
 static TEST_AUTH_TEMP_DIRS: Lazy<Mutex<Vec<TempDir>>> = Lazy::new(|| Mutex::new(Vec::new()));
 
 #[derive(Debug, Error)]
@@ -1111,6 +1112,18 @@ impl AuthManager {
         })
     }
 
+    #[cfg(any(test, feature = "test-support"))]
+    /// Create an AuthManager with a specific CodexAuth and codex home, for testing only.
+    pub fn from_auth_for_testing_with_home(auth: CodexAuth, codex_home: PathBuf) -> Arc<Self> {
+        let cached = CachedAuth { auth: Some(auth) };
+        Arc::new(Self {
+            codex_home,
+            inner: RwLock::new(cached),
+            enable_codex_api_key_env: false,
+            auth_credentials_store_mode: AuthCredentialsStoreMode::File,
+        })
+    }
+
     /// Current cached auth (clone). May be `None` if not logged in or load failed.
     pub fn auth(&self) -> Option<CodexAuth> {
         self.inner.read().ok().and_then(|c| c.auth.clone())