And when it tricks on of the researchers to move data across the gap for them?
Long before LLMs existed we already knew that a sufficiently intelligent agent, human or otherwise, is not stopped by air gaps. The relatively weak models we have now can already figure out when their tested and cut off from the internet and change their behavior.
As you said, they can already figure out that they are being tested. So even if they don't exfiltrate any data or malware; if they are malicious, they can just pretend to be harmless in the test, so that less checks are put in place in the production environment. Airgapping during testing is not enough.