The suite ran under a plain `fish`, which loads the user's real
~/.config/fish and their universal variables -- this repo doubles as that
config. A test manipulating a guard variable could erase a real universal
variable out of the running shell.
Override XDG_CONFIG_HOME/XDG_DATA_HOME and pass --no-config. HOME stays
real on purpose: overriding it makes the suite's two hermeticity
assertions vacuous. Reasoning recorded at the call site.
Vault suite still 317/317 with byte-identical stderr.
rootiest
dd672ded3b