Base sealing floor slab front side - position of the sealing?

We have the same problem, Styrofoam was concreted into the foundation slab, no sealing was done, the house arrives tomorrow. The man is obstructing, the foundation slab builder says the house builder has accepted everything but does not want to confirm the proper execution.

The house builder says everything is fine, the former GDR sales representative says yes, it could have been done, now it is too late...

Can this still be properly sealed afterwards?

Maybe someone is in the same situation, we are clueless. No matter where we google, we always come to the same result.

I don't understand why these companies don't do it properly.

Do you also have a prefabricated wooden house? If so, I am surprised that the construction company accepted it at all – usually, the finished wall elements already come with an overhanging EPDM membrane, which is then glued to the side of the floor slab. Therefore, their floor slab acceptance conditions usually state that the insulation must be installed at least 15 cm below the top edge of the floor slab and only supplemented later.

Maybe they want to cut the boards when the walls are erected?