Beautiful bike. I remember when you first acquired it. Glad to see it's still around. The work sculpting those shifters is quite something. And the bars/stem combo!

Yes, I believe this would be considered fillet brazing. It does remind me of my Speedwell Titalite (album link), though the Passoni is more elegant and carefully constructed. My Speedwell seat cluster looks crude by comparison.

Thinking out loud...If it was rolled, seamed, and polished smooth, shouldn't you be able to see the seam on the inside of the tubes? You could pull the post and stem and have a look inside, right? Surely, the inner part of the seam would not have been polished. Even if the tubes were reamed, there would still be some visible trace.