Did Juju ever error as opposed to warn about config attributes that didn't match the schema? For a long time, Juju had no way of allowing model config that was provider specific, so it had to allow unknown attributes to be set - the provider would use them but the attribute was unrecognised by Juju's config schema. eg AWS clouds can have a vpc-id, Openstack can have use-floating-ip etc. So Juju just used to warn about such values. And I suspect that behaviour still exists today. Or are you saying for controller config, we used to be more strict and genuinely did error?
Did Juju ever error as opposed to warn about config attributes that didn't match the schema? For a long time, Juju had no way of allowing model config that was provider specific, so it had to allow unknown attributes to be set - the provider would use them but the attribute was unrecognised by Juju's config schema. eg AWS clouds can have a vpc-id, Openstack can have use-floating-ip etc. So Juju just used to warn about such values. And I suspect that behaviour still exists today. Or are you saying for controller config, we used to be more strict and genuinely did error?