Treat refresh_token_reused 400s as relogin-required (#24830)

## Summary
- classify known refresh-token terminal failures from `/oauth/token` as
permanent even when the backend returns `400`
- preserve the existing relogin-required message for
`refresh_token_reused` instead of retrying and collapsing into a generic
cloud requirements error
- add regression coverage for `400 refresh_token_reused`

## Testing
- `just fmt`
- `cargo test -p codex-login`

codex-rs/login/tests/suite/auth_refresh.rs

@@ -625,6 +625,73 @@ async fn refresh_token_does_not_retry_after_permanent_failure() -> Result<()> {
     Ok(())
 }
 
+#[serial_test::serial(auth_refresh)]
+#[tokio::test]
+async fn refresh_token_does_not_retry_after_bad_request_reused_failure() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = MockServer::start().await;
+    Mock::given(method("POST"))
+        .and(path("/oauth/token"))
+        .respond_with(ResponseTemplate::new(400).set_body_json(json!({
+            "error": {
+                "code": "refresh_token_reused"
+            }
+        })))
+        .expect(1)
+        .mount(&server)
+        .await;
+
+    let ctx = RefreshTokenTestContext::new(&server).await?;
+    let initial_last_refresh = Utc::now() - Duration::days(1);
+    let initial_tokens = build_tokens(INITIAL_ACCESS_TOKEN, INITIAL_REFRESH_TOKEN);
+    let initial_auth = AuthDotJson {
+        auth_mode: Some(AuthMode::Chatgpt),
+        openai_api_key: None,
+        tokens: Some(initial_tokens.clone()),
+        last_refresh: Some(initial_last_refresh),
+        agent_identity: None,
+    };
+    ctx.write_auth(&initial_auth).await?;
+
+    let first_err = ctx
+        .auth_manager
+        .refresh_token()
+        .await
+        .err()
+        .context("first refresh should fail")?;
+    assert_eq!(
+        first_err.failed_reason(),
+        Some(RefreshTokenFailedReason::Exhausted)
+    );
+
+    let second_err = ctx
+        .auth_manager
+        .refresh_token()
+        .await
+        .err()
+        .context("second refresh should fail without retrying")?;
+    assert_eq!(
+        second_err.failed_reason(),
+        Some(RefreshTokenFailedReason::Exhausted)
+    );
+
+    let stored = ctx.load_auth()?;
+    assert_eq!(stored, initial_auth);
+    let cached_auth = ctx
+        .auth_manager
+        .auth()
+        .await
+        .context("auth should remain cached")?;
+    let cached = cached_auth
+        .get_token_data()
+        .context("token data should remain cached")?;
+    assert_eq!(cached, initial_tokens);
+
+    server.verify().await;
+    Ok(())
+}
+
 #[serial_test::serial(auth_refresh)]
 #[tokio::test]
 async fn refresh_token_reloads_changed_auth_after_permanent_failure() -> Result<()> {