We know the Egyptians used soft copper saws and a slurry of fine sand and water ... why couldn’t something the size and shape of a jointer plane be used with a copper shoe (instead of a rotating disk saw) on the inside of such a box?
Interior corners could be achieved with something like a molding plane.
The actual cutting is with the grit and water, not the hand tool, and by using a long tool flatness is easier to achieve.
Best of all, this idea should be testable to see if it even works.
This theoretical solution of copper saws and abrasive have been debunked. While proven possible given the location of many saw cuts, copper saws are just considered not feasible.
In the numerous saw cut examples and especially in the quarries, there are large radiused circular saw marks in the stones. Some sort of circular saw was apparently used. There are lots and lots of the circular saw marks
Actually, we don’t know.
Academics writing papers have made the claim about copper saws and they have made videos of the process working. They have not however actually made any thing
The same is true of tube drills. Today in my former shop, there are slotted brass tubes used with water and carbide grit to drill precise large diameter holes in glass.