A further but less important question is that why temporary path is not affected by missing environment variables? If macOS can figure out correct sandbox paths without environment variables, why not all of them doing so?

I finally solved it! It is environment variables that determine the behavior. The helper app was designed to accept some environment variables given by caller, but in our latest developement implementation, only those environment variables are given, without those from electron app. After I added them back, those APIs work as expected. Thanks for your helpful assistance!

Thanks for your kind instructions. I have tried the following steps: I followed your step and reproduced correct behavior. I replaced my helper app with child.app and child.app got /Users/<me> for home. I replaced child.app with my helper app and my helper app got expected home at /Users/<me>/Library/Containers/<app_id>/Data. Now it looks like to have something to do with how helper app is launched by electron app.