Could not launch testcase process. Is 'python3' in your PATH?

[ltdt-apex]

I am trying to run cph with python inside docker, however it keeps complaining python3 not in path even tho it is.

Dockerfile definition

FROM python:3.9.10-slim

CMD sleep infinity

my PATH

root@73336472a8cd:/workspaces# printenv | grep PATH
PYTHONPATH=/usr/local/bin
PATH=/root/.vscode-server/bin/b3e4e68a0bc097f0ae7907b217c1119af9e03435/bin/remote-cli:/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

python location

root@73336472a8cd:/workspaces# which python3
/usr/local/bin/python3

root@73336472a8cd:/workspaces# ls -la /usr/local/bin | grep python
lrwxrwxrwx 1 root root    22 Mar  2  2022 python -> /usr/local/bin/python3
lrwxrwxrwx 1 root root    29 Mar  2  2022 python-config -> /usr/local/bin/python3-config
lrwxrwxrwx 1 root root     9 Mar  2  2022 python3 -> python3.9
lrwxrwxrwx 1 root root    16 Mar  2  2022 python3-config -> python3.9-config
-rwxr-xr-x 1 root root 14416 Mar  2  2022 python3.9
-rwxr-xr-x 1 root root  3079 Mar  2  2022 python3.9-config

directly running python3 do not have any problem

root@73336472a8cd:/workspaces# python3
Python 3.9.10 (main, Mar  2 2022, 04:31:58) 
[GCC 10.2.1 20210110] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 

however, running cph gives

Could not launch testcase process. Is 'python3' in your PATH?

I have also tried different python command prefix, like python, python3, python3.9, all not working.

Do I need to configure something in VScode side to make it works?