The openidm-zip packaging phase includes several steps. Namely,
1. unzip the packaged openidm-7.0.0-SNAPSHOT.zip
2. run the checksum plugin to generate a .checksums.csv of all files in the zip
3. add the .checksums.csv file to the zip
The truezip plugin uses openidm-zip/target/tmp as it's temporary extract location for the purposes of running the checksum plugin on this directory. When finished, the tmp directory is left behind creating unnecessary disk waste. This directory could be removed after the truezip plugin steps to reduce disk space.