So just for completeness' sake, the remainder of the story is that I went in two weeks ago for the second cystoscopy, and the doctor very quickly spotted the polyp. He gave me the choice of doing a complete TUR right there or coming back for an anaesthetic procedure---it was very small, he said. Considering that this started with a stone and that I was already trussed up and be-endoscoped, I suspected I did not really need the anaesthetic and told him to do it.
It was the right choice. A few minutes of cutting and fulguration---felt like butterflies or something---and he had what really was a tiny speck out of me. Sent for pathology.
Anyway, the second pathology also agrees that it's a benign papilloma, but of course, it is not over---I must go for regular cystoscopies I guess indefinitely now. The chance in a patient of my age for it to turn to something malignant is thank God kind of low, but I am a Known Risk now, I guess. This is probably all not good for my prospects of getting life insurance, but whatever