The LUCI-ENGINE check is defined in this file https://github.com/flutter/cocoon/blob/master/app_dart/lib/src/request_handlers/push_engine_status_to_github.dart#L54

It does not appear to be considering the case where the latest build for a builder is pending, but the previous build failed. The desired behavior in this situation is to return failure, and wait for a green build. https://github.com/flutter/cocoon/blob/master/app_dart/lib/src/request_handlers/push_engine_status_to_github.dart#L110