Apron flashing was installed at the shed roof-to-wall intersection.
The picture shows the apron flashing being installed. You can also see where the underlayment (felt paper) has been wrapped up the vertical wall 12”.
The apron flashing should be installed over the shingles and then should have the HouseWrap laid back over the vertical portion of the apron flashing. This will help to ensure the drainage plane stays continuous and that all materials have been installed shingle style.