Trying to workaround the 4th like that might manage to make the law facially constitutional, but I'd be surprised if it made the searches conducted as a result

Trying to workaround the 4th like that might manage to make the law facially constitutional, but I'd be surprised if it made the searches conducted as a result of it valid. By my understanding you have to avoid a "warrantless search by a government agent" to avoid violating the constitution. The "warrantless search" part is really beyond dispute, so it's the "government agent" part that is in question. In general "government agent" is a term of art that means "acting at the behest of the government", but I don't know exactly where the boundary lies. I'd be fairly surprised if any law that allowed for accidentally storing CSAM after a failed search, but didn't allow for accidentally storing CSAM content without a search, didn't make the party doing the search a government agent. If you make the former illegal, cloud storage at all (scanning or not) is an impossible business to be in.