Krikri::FirstFoundLookupError
Raised by the first_found lookup (ExpressionEvaluator's
#evaluate_first_found) when no candidate file exists and the lookup's
own skip: param is not true - real Ansible's own failure for that
shape ("The lookup plugin 'first_found' failed: No file was found when
using first_found.", verified live against 2.19.4), NOT the "undefined"
sentinel string the code path used to return (which became "include_
vars: file not found: undefined" at the include_vars: consumer).