I am trying to build a micromamba based container, that automatically activates the correct environment.

Apptainer.def

Bootstrap: docker
From: mambaorg/micromamba:1.5.8

%files
    environment.yaml /environment.yaml

%post
    micromamba create -n __apptainer__ && 
    micromamba install -n __apptainer__ --file environment.yaml && 
    micromamba clean --all --yes

    # Activate the environment and set it as default when starting the container
    echo "source /opt/conda/bin/activate __apptainer__" >> $SINGULARITY_ENVIRONMENT

    # Update PATH to include micromamba binaries and other environment variables
    echo 'export PATH="/opt/conda/envs/__apptainer__/bin:$PATH"' >> $SINGULARITY_ENVIRONMENT

    # Add micromamba shell hook and activation to Singularity environment script
    echo '/usr/bin/micromamba activate __apptainer__' >> $SINGULARITY_ENVIRONMENT

environment.yaml

name: __apptainer__
channels:
  - conda-forge 
dependencies:
  - jupyterlab

after building the container with apptainer build jupyter-lab-micromamba.sif Apptainer.def, I get this:

apptainer shell jupyter-lab-micromamba.sif

Apptainer> micromamba env list
  Name           Active  Path                         
────────────────────────────────────────────────────────
                 *       /home/username/miniforge3   
  base                   /opt/conda                   
  __apptainer__          /opt/conda/envs/__apptainer__
bash: __vte_prompt_command: command not found
Apptainer> micromamba activate __apptainer__

'micromamba' is running as a subprocess and can't modify the parent shell.
Thus you must initialize your shell before using activate and deactivate.

To initialize the current bash shell, run:
    $ eval "$(micromamba shell hook --shell bash)"
and then activate or deactivate with:
    $ micromamba activate
To automatically initialize all future (bash) shells, run:
    $ micromamba shell init --shell bash --root-prefix=~/micromamba
If your shell was already initialized, reinitialize your shell with:
    $ micromamba shell reinit --shell bash
Otherwise, this may be an issue. In the meantime you can run commands. See:
    $ micromamba run --help

Supported shells are {bash, zsh, csh, xonsh, cmd.exe, powershell, fish}.
critical libmamba Shell not initialized
bash: __vte_prompt_command: command not found
Apptainer> eval "$(micromamba shell hook --shell bash)"
bash: __vte_prompt_command: command not found
Apptainer> micromamba activate __apptainer__

I tried to run this during %post: eval "$(micromamba shell hook --shell bash)", but that also produces problems. How must this be done, so that the correct enviroment is automatically active?