Forgot insulation on the dormer wall - mold on wood - what to do?

In our contract, it is clearly stipulated that our general contractor also takes on the construction management and, among other things, monitors the quality of the individual trades and intervenes if necessary.

It is like that in every general contractor contract. In case of doubt, it will not help you. Just to recognize shoddy work, you need an expert. Do yourselves a favor and find one who does not only become active when you have already discovered the shoddy work.

That was a bad decision

Yes.

, but no longer changeable now.

No.

Methodically, handled it exemplarily in post #12 in my opinion.
For me, there would be no wavering between options here, since I consider the principle "always stop the bleeding before sewing up" to be indisputably unshakable. In this respect, I have doubts about the insight of the GU and apparently see him as believing that everything will be fine with the improvement of the missing insulation. No, of course the cause must be eliminated first. But that would also be said by the expert, whom one better involves late than never – admittedly not as a pathologist who may be right but can no longer heal ;-)