Ornamental Corinthian peach trees will work there. No root problems, all the branches grow upright and the tree will not overcrowd the space. There are several cultivars of these which bloom different colors. They do best planted in full sun and in well draining soil. You can choose from those which bloom pink, red, or white. quite beautiful trees year round. solid cover blooming before red colored leaves emerge. the red leaves change to green in the hottest part of summer, and then any new growh on the tips of the branches in Fall emerges out red again. Branches never thicken enough to cause weak crotch breakage problems. 'Franz Fontain' hornebeam trees would also work just fine there without producing damaging rooting patterns. These are quite nice trees, but while young stay extra narrow for quite some time. Still if you have the patience to wait they mature into a very nice still narrow enough tree. Both of these trees do well in full sun exposure, and will grow tall enough to provide the shading you want, with out overcrowding the area. Only thing about the Franz Fontain hornbeam tree, either be prepared for a really young 4-5 foot tall tree to take quite a few years to fill out enough to begin doing much of the shading you desire. If that is the tree you choose, then it is worth paying more for one that has grown and spread to the least size, that your patience will endure in the spot where you want it planted.

I know you were thinking of perennials, but I am suggesting mostly low growing, drought tolerant shrubs. I have hardly ever seen blue rug, and some of the other ground cover evergreens fail in full sun and dry soil. If daffodils and other bulbs that like dry Summer soil were placed here and there you would have color for a few weeks. Or you could just have shades of green, greygreen, bluegreen and silvery blue. Check out juniperus 'Blue Star'. I also have the interesting one called 'Pancake' that is the flattest of all. There are untended and bone-dry railroad embankments, locally, that have a Summer cover of Lathyrus latifolia and daylilys. Here in the pine barrens Arctostaphyllos ova-ursi is growing on the sandy roadsides totally ignored and beautiful. Also the plant called sweetfern, which is not green in winter but as tough as nails, two feet tall and naturally spreading.

Any trees big enough to cast shadows as large as you want will 1. Take years to develop to that size 2. Will almost certainly be too big for the available space In fact there is no in-ground space for a tree at all where you have the existing canopy set up. However the climbing plant that is growing from the bed up onto the corner of the house does suggest the alternative solution of putting up a trellis or arbor and furnishing that with a fast growing climber. This approach would have its own issues of course, including a need for effective annual pruning and training, to get the climber to assume and maintain the desired shape. And not damage the downspout or other parts of the house. And the climbing plant dropping litter onto the drive (as trees would do also). And the installation becoming a possible highway for rats up onto the house (as trees planted so close to the house would probably be also).

Where are you in the PNW that routinely sees July temps in the 90's or above? I have lived and gardened here all my life and have yet to encounter a similar situation. Most part shade plants will tolerate those conditions with ease, although I would not include bigleaf hydrangea in that mix. There is not much that can't handle late afternoon PNW sun as long as one supplies it with adequate water......... ETA: Interior valleys where precisely.......if on the eastern side of the Cascades, that is a significant departure from what is typical PNW growing conditions.