Interesting! I wonder if it’s because our docker image now includes discourse-cakeday, and then when core is “downgraded” to 3.5, it leaves an empty directory behind.
If you add rm -rf discourse-cakeday before the git clone https://.../discourse-cakeday line, then that should clean it up. So it would look something like:
hooks:
after_code:
- exec:
cd: $home/plugins
cmd:
- rm -rf discourse-cakeday
- git clone https://github.com/discourse/discourse-cakeday