# InvariantRequiresAxiom: nodes with invariant=true must have level='Axiom.
# Apply as a post-schema constraint on individual Node records.
std.contract.custom (
  fun label =>
    fun value =>
      if value.invariant && value.level != 'Axiom then
        'Error {
          message = "Node '%{value.id}': invariant=true requires level='Axiom (got '%{std.string.from value.level})"
        }
      else
        'Ok value
)