Recessed windows on a mansard roof are a flashing nightmare and guaranteed to leak. I would agree a drip edge flashing would be needed. Water adhesion will cause the rainwater to run under the edge without one.
That’s not really a mansard issue. That is an issue with using shingles as siding in a window alcove. And, using what looks like plywood as a decorative arch without properly cladding it…what a bad idea. That will never be right if left like that.
There is flashing available for use at round widows that is basically like this. One flange is cut into sections so that the flashing will bend around curves.
I see the sill as being a more serious issue. To be really waterproof, this type of sill should have one-piece metal pan-flashing, which must be custom made for the opening.
Just spoke with the client doing a follow up call.
A regular refering Agent had referred me to this Agent from what I heard through the grape vine she was not happy with me because the 2800 sq foot place with gravel crawlspace and Mansard roof took over 3 1/2 hours but she gave me stink eye on arrival so when I called the client immediately said who cares we are paying you and you may have saved us over $17,000 plus my Lawyer loved all the detailed images that prove the pointed out problems.
“My Lawyer was gushing and is going to be referring you in the future”. [she said to me ]
Moral of the story is to care about the person who pays you and do the job as you see fit.
Side note is the Agent I know just met a guy today who made them all sit 20 minutes while he wrote out a report with no pictures and when asked to take a few pictures of the mold in the attic for the attorneys he got all hot and bothered and screamed at the Agent to report him if he doesn’t like it (lack of photos) .
The clients had gone with their Lawyers referral…:)…go figure.