A guard can watch the cell through a composter. The walls regenerate using a cobblestone generator. Visitors enter through the ceiling, and the prisoner respawns from below using the squilly bed glitch and a boat.
Outside defence
Surrounding the prison are many layers of Hi_There's lava grid surrounding regenerating piglin bans, making using a wither painful. Above the prison there is an unbypassable mining detector.
Extra Security
The killcheck beds have hoppers underneath them to prevent normal item smuggling. The guards will do an area kick test to make sure there is only one player in the entrance portal area. Every important area is in range of elder guardians, which will give constant mining fatigue. Visitors have to click an exit bed, to stop them from getting back into the last killcheck.
