Zkg - safe clean-up after install, Docker image

I’m trying to minimize image sizes when running zkg during a Docker image build:

RUN zkg install --force seisollc/zeek-kafka --version v1.2.0 --user-var librdkafka_root=/usr && \
    rm -rf /usr/local/zeek/var/lib/zkg/scratch /usr/local/zeek/var/lib/zkg/testing && \
    zeek -N Seiso::Kafka

Notice the rm from scratch and testing - are both of those safe to delete i.e. are temp build artefacts?

In the same directory, deleting clones seemed to have side-effects:

zeek -N Seiso::Kafka
internal error: Failed to find variable named: Kafka::kafka_conf

Is that expected, despite the lib being built into /usr/local/zeek/lib/zeek/plugins/packages/zeek-kafka ?

Is there any documentation on what is safe to clean-up post zkg install?