If a controller is deleting correlations from your sense data, that makes discovering causality harder, and it seems difficult to say "aha, causality is harder to discover than normal, therefore there are controllers!", but that might actually be effective.

Yes, in the PCT field this is called the Test for the Controlled Variable. Push on a variable, and if it does not change, and it doesn't appear to be nailed down, there's probably a control system there.

I have an unpublished paper relating the phenomenon to causal analysis à la Pearl, but it's been turned down by two journals so far, and I'm not sure I can be bothered to rewrite it again.