Yeah it's flashed. Slid a piece of flashing under each shingle and up under the siding. Finished it at the bottom by cutting a slot in the siding and bringing that flashing out over the drip edge. Will also slide in j channel to finish off the siding. I roofed for 5 years so that part was a breeze.
Lower right corner you can see the flashing
Doesn't the flashing need to go under the siding and over the shingles? Seems like the water can run into the corner and follow that flashing right under the shingles to attack the underlayment the way you described it.
BTW, nice fast build!