And not in a windowless room already.

How many air gapped systems are running next to a Window?

Although I guess you can use this as evidence: if it needs to be air-gapped it also needs to be in a windowless room or some kind of sealed container.

How long before we have people shooting cosmic rays at air-gapped systems in windowless rooms and measuring bit flips?

Most of the time the system is compromised before being in an air gapped setup, for instance in the supply chain.