On closer inspection, the stress indicator showing on the front of the head tube lines up with a manufacturing defect in the carbon.
The carbon became creased before curing in the mould, creating a weak spot that has then failed under normal loads. The analogy we often use to describe this kind of defect is a plank of wood failing due to the fibres curving round a knot. If the fibres aren't running perpendicular to the load, then they can't distribute that load down their length, and the bond between the layers stands to fail.
In this kind of instance we pass on the details to the customer who can then pursue a warranty claim. You've just got to cross your fingers that the warranty department does the right thing!