secret files are sometimes overwritten by an empty file

I don't know exactly how to reproduce this (ideas below), but occasionally I'm noticing that /etc/debci/${worker}.key is replaced by an empty file. When that happens, doing a rake converge doesn't help; it seems I need to manually delete files in the rsync location on the worker.

Potential root causes:

• The worker is listed in nodes.ignore
• I'm too late with providing my passphrase to gpg
• I fail to provide the right passphrase to gpg