Also an exterior sheathing that has an integral air and water barrier then taped and sealed to the window mullion flashing can also act as that control layer.
The mechanical fastening system must not create a thermal bridge through the ridged continuous insulation. Knight Wall Systems or equal provide a thermally broken skin attachment system.
Outboard sealant protects main sealant from the environment and acts as a first line of defense in line with the exterior face of glass and not block weeps.
In cases where the UL for rated roof requires exterior rated sheathing laid on the metal deck the air /water barrier can continue under the roof insulation but must meet roofing system warranty.