Tests, written before the change, for the check of PIXA_ names at
startup: a PIXA_ variable that is not a setting's variable aborts naming
it, PIXA_PORT aborts with a message saying to use PORT, and
PIXA_CONFIG_PATH and every setting's variable are accepted. They call
validateKnownEnvVars, which the change adds, so the package does not
build until it lands.
Model: opus-5-5