What I am after may not exist. Tails without a clearnet browser would be close. It would be ideal if the platform were clearnet-free out of the box. Even better: clearnet incapable.
If I would uninstall the clearnet browser, that would be a deliberate act on my part to have a broken clearnet. It would be indefensible. The idea is to most faithfully play dumb when fighting public administrations who block tor.