Why don't construction prices go down?

The wall stands and no one will tear it down because of a cm/mm planning issue.

Possibly true. But to consider the argument insignificant in the case of an error of almost 10cm is not a good approach either. That masons rarely pay attention to the cm and certainly not to the mm is okay. But the dm is indeed an order of magnitude that you need as a margin of safety, for example for kitchens.

Our general contractor said that the octameter applies on his construction site. Therefore 3.875m, 4m, 4.125m, Otherwise the mason would have to cut every row of bricks. If the kitchen is supposed to be 4m deep, the rough construction dimension is 4.125m. Planning error

Otherwise, the mason would have to cut every row of bricks. If the kitchen is supposed to go 4m in, the shell construction measurement is 4.125m. Planning error

If 3.98 came out, obviously it was cut anyway. So why not just go close to the correct measurement from the start? But it is correct that, as you described, everything is easier and less prone to errors.

If it came out as 3.98, it was obviously cut anyway. So why not just cut it close to the correct measurement right away?

Because it is only cut once (undersized), and not in small slices up to 4m, Our kitchen is also 4m, and the rough construction measurement was 4.125m

We had the kitchen planned according to the work plan... If I can't rely on that, then what can I? The billing will be 100% too, so I expect at least 95% execution...

And 6.6cm for 2x plaster + tolerance is not excessively tight planning in my opinion...

4.07m no bricklayer can do, he just doesn't admit it.
If you have such fantasy measurements everywhere, outside the octameter,
I would now measure the entire shell construction (walls, doors, windows, etc.)