Alright good news… I’ve figured it out! It seems having a newline at the end of the cache key is the issue underlying this vague caching exception.
Old: use of >. This used to work, but apparently it doesn’t work any more, this will raise the error encountered (see original message).
key: >
deps1-{{ .Branch }}-{{ .Environment.CACHE_VERSION }}-
{{ checksum "foo.txt" }}-
{{ checksum "bar.txt" }}-
...
{{ checksum "last.txt" }}
New: use of >-. This - (per YAML) strips the final newline in the output. This works for me!
key: >-
deps1-{{ .Branch }}-{{ .Environment.CACHE_VERSION }}-
{{ checksum "foo.txt" }}-
{{ checksum "bar.txt" }}-
...
{{ checksum "last.txt" }}