Could you tell how deep is your seatpost in the seat tube ?
To my untrained eyes, this looks like your seat post slipped down too much and hit the frame. That caused the crack. Hardly the manufacturers fault etc. IF they honour this, you are a lucky dude.
The seat post should have been cut properly during the original assembly.
The seatpost was inserted to a depth of 17,5 cm, with the '10 marking' positioned roughly 0,5 cm above the frame opening.
The post never slipped during use. The frame’s maximum insertion depth is indicated by the '13 marking,' meaning there was still 3 cm of clearance between the end of the seatpost and the internal of the frame, more than enough safety margin. I have attached photos of the bottom of the seatpost to show there are absolutely no impact marks or signs of bottoming out. You can make out the insertion depth by the carbon grip compound.
For context: I am a mechanical engineering graduate student and have previous professional experience working in bike shops. I am very meticulous with maintenance; all bolts were tightened to spec using a calibrated torque wrench, and assembly was done following best practices.