User and group app:app does not exist in multistage.Dockerfile

[toshikish]

In multistage.Dockerfile L24, /app directory is copied from builder stage with --chown option.
But the specified user and group app:app is not added in base, builder and final images.

• Building an image using Kaniko fails with error message: error building image: error building stage: failed to execute command: getting user group from chown: user app is not a uid and does not exist on the system.
• Building an image using buildx succeeds, but the copied directory owner is root:root.

root@91cf9a664aef:/# ls -al /app
total 136
drwxr-xr-x 6 root root  4096 Nov 19 01:27 .
drwxr-xr-x 1 root root  4096 Nov 19 01:31 ..
-rw-r--r-- 1 root root    66 Nov 19 01:26 .dockerignore
drwxr-xr-x 7 root root  4096 Nov 19 01:26 .git
drwxr-xr-x 3 root root  4096 Nov 19 01:26 .github
-rw-r--r-- 1 root root    30 Nov 19 01:26 .gitignore
drwxr-xr-x 4 root root  4096 Nov 19 01:27 .venv
-rw-r--r-- 1 root root  1216 Nov 19 01:26 Dockerfile
-rw-r--r-- 1 root root  3465 Nov 19 01:26 README.md
-rw-r--r-- 1 root root   775 Nov 19 01:26 compose.yml
-rw-r--r-- 1 root root  1139 Nov 19 01:26 multistage.Dockerfile
-rw-r--r-- 1 root root   405 Nov 19 01:26 pyproject.toml
-rwxr-xr-x 1 root root   966 Nov 19 01:26 run.sh
drwxr-xr-x 3 root root  4096 Nov 19 01:26 src
-rw-r--r-- 1 root root 77872 Nov 19 01:26 uv.lock

It would be better to add user and group beforehand.