fix: auth.json leak in tests (#18657)

Before this some tests were leaking an auth.json file into
`codex-rs/core`. This just fixes it

codex-rs/login/src/auth/auth_tests.rs

@@ -230,6 +230,33 @@ fn chatgpt_auth_persists_agent_identity_for_workspace() {
     assert_eq!(auth.get_agent_identity("account-123"), None);
 }
 
+#[test]
+fn dummy_chatgpt_auth_does_not_create_cwd_auth_json_when_identity_is_set() {
+    let cwd_auth = std::env::current_dir()
+        .expect("current dir")
+        .join("auth.json");
+    let had_auth_json_before_test = cwd_auth.exists();
+    let auth = CodexAuth::create_dummy_chatgpt_auth_for_testing();
+    let record = AgentIdentityAuthRecord {
+        workspace_id: "account_id".to_string(),
+        chatgpt_user_id: None,
+        agent_runtime_id: "agent_123".to_string(),
+        agent_private_key: "pkcs8-base64".to_string(),
+        registered_at: "2026-04-13T12:00:00Z".to_string(),
+    };
+
+    auth.set_agent_identity(record.clone())
+        .expect("set agent identity");
+
+    assert_eq!(auth.get_agent_identity("account_id"), Some(record));
+    if !had_auth_json_before_test {
+        assert!(
+            !cwd_auth.exists(),
+            "dummy ChatGPT auth must not write auth.json in the test process cwd"
+        );
+    }
+}
+
 #[test]
 fn unauthorized_recovery_reports_mode_and_step_names() {
     let dir = tempdir().unwrap();

codex-rs/login/src/auth/manager.rs

@@ -13,6 +13,8 @@ use std::path::PathBuf;
 use std::sync::Arc;
 use std::sync::Mutex;
 use std::sync::RwLock;
+use std::sync::atomic::AtomicU64;
+use std::sync::atomic::Ordering;
 use tokio::sync::Mutex as AsyncMutex;
 use tokio::sync::watch;
 
@@ -96,6 +98,7 @@ const REFRESH_TOKEN_URL: &str = "https://auth.openai.com/oauth/token";
 pub(super) const REVOKE_TOKEN_URL: &str = "https://auth.openai.com/oauth/revoke";
 pub const REFRESH_TOKEN_URL_OVERRIDE_ENV_VAR: &str = "CODEX_REFRESH_TOKEN_URL_OVERRIDE";
 pub const REVOKE_TOKEN_URL_OVERRIDE_ENV_VAR: &str = "CODEX_REVOKE_TOKEN_URL_OVERRIDE";
+static NEXT_DUMMY_AUTH_ID: AtomicU64 = AtomicU64::new(1);
 
 #[derive(Debug, Error)]
 pub enum RefreshTokenError {
@@ -442,7 +445,11 @@ impl CodexAuth {
             auth_dot_json: Arc::new(Mutex::new(Some(auth_dot_json))),
             client,
         };
-        let storage = create_auth_storage(PathBuf::new(), AuthCredentialsStoreMode::File);
+        let dummy_auth_id = NEXT_DUMMY_AUTH_ID.fetch_add(1, Ordering::Relaxed);
+        let storage = create_auth_storage(
+            PathBuf::from(format!("dummy-chatgpt-auth-{dummy_auth_id}")),
+            AuthCredentialsStoreMode::Ephemeral,
+        );
         Self::Chatgpt(ChatgptAuth { state, storage })
     }