Mystery Succulent (Can You Help?)

A few years ago, while on a shopping expedition to Native Revival (one of my favorite nurseries), I picked up two 4-inch pots with an attractive, fleshy, blue-green succulent. When I asked a person on staff what it was, she said:"Oh, that's not a native. We stock it because people want them." And no, she did not know what it was. Well, it was on sale and so I took it home.

At first I thought it was a kind of Senecio, but then the blossoms appeared, and I realized I had no idea what I had. 

But whatever it is, it is quite happy in my garden! Each winter, the plants seem to double in size. They are easily transplanted, and I've tucked them into containers and put them in the sunny, dry, front garden. While other succulents almost don't make it through the dry summers or succumb to the light frost we sometimes get, this plant seems to love it here.

So, does anybody know? My mystery sedum taller than the blueish Senecio (the first photo has it next to a chair for comparison). Flowers in late spring. Reblooms. Tolerates light frost. Sadly nameless for several years now...