The short question: Does anyone know what this plant is and whether it is a flowering perennial or a weed?

The long version: Have you ever been puzzled in the spring by whether an emerging plant is something you put there or a weed? If so, then you understand the situation I'm in. This is now the second season for the perennial bed I put in on the southwest side of my house in 2014. I planted salvia, phlox, foxglove and a few other things but, unfortunately, didn't keep good records about what I planted. Figured I'd remember. I was wrong. I can't for the life of me remember what this plant is and I fear that I might be mollycoddling a weed with water and fertilizer that I instead ought to be yanking out. If it's any help, I'm in the U.S. Midwest in south central Wisconsin (Zone 5A).

The plant just seems too darned neat and well-mannered to be a weed but I simply don't know. It's now about four feet high, if not an inch or two higher. The main stem of the plant has flattish sides, like a hexagon or octagon. I see no evidence of flower buds.

Anybody recognize this thing? I'm actually a little embarrassed to be asking the question as it makes me look a bit silly but, as the old New Yorker cartoon informed us, on the Internet no one knows you're a dog.