`checks.script-test-nats-render-config` runs the queue server's
`ExecStartPre` render against a scratch runtime directory: a fetched key
lands in `auth_callout.xkey` and the wrapper includes the fragment, and
a missing or malformed key file fails the start and writes no config.
module-eval only sees the render as a store path, so dropping `xkey`
from the template, or its substitution, passed every check while the
server would have run unsealed.
