Connection for washing machine was forgotten in the new building

which is listed in the construction service description.

It would be interesting to know whether it was also included in the planning. Many things can be stated in the construction service description, especially if something is agreed upon or signed for the planning. For example, we also have a washbasin in the utility room listed in the construction service description, which we did not include in the planning due to opting out. And why have you only noticed it now? It doesn’t read like you live 100 km away. As a client, you do check quite a bit on the construction site…

Presumably, he will use the inlet and outlet from the washbasin, yes.
I think the effort for embedding the installation in the wall is no longer proportional. Besides, the washing machine, like the washbasin, will cover most (if not all) of it, so you don't have to be overly particular now.
However, I would negotiate something, for example a separate circuit for the washing machine or a built-up pedestal. Something. That provides clearer added value.

The question is whether it is even that simple to use the washbasin’s inlet. In our case, the water pipe runs inside the wall up to the faucet. From there, the inlet was tapped off as a separate water tap, but of course already embedded in the wall. That would not be feasible afterwards. And the washing machine does need its own water tap.

A separate circuit for the washing machine is standard.

A individually protected socket can be surface-mounted.

Hello, I wanted to get in touch after all. Since we had a socket for the washing machine, we have now agreed to connect it completely at the washbasin. Unfortunately, it was probably a communication problem. In the construction description, only the connection was mentioned, but nothing specific. This was then discussed. It will still get a faucet, but since it is right next to the washbasin, this is probably not a problem.