Docker image contents not visible at runtime in Jenkins Kubernetes agent pods

We are trying to demonstrate a pytest-based OpenSCENARIO engine validation tool in the gt-gen-simulator pipeline.

Our plan was to create a docker image with all our dependencies and the pytest suite and run this in a separate container in the pipeline so that we can also access the gt-gen binary.

But files like dependencies/poetry that exist in the image's file system are not visible at runtime in the Jenkins Kubernetes agent pods. I've tried several directories (/usr/local/, /opt, ..) and noticed that sporadically some of my docker image's content (e.g. poetry) appears but most of the time it's overwritten/not mounted.

Where can we safely write to in a docker image so that it is available in the pipeline later? Where should we install tools like Poetry? Where can we clone our repo so it survives? Are there recommended paths or patterns for building images for this environment?