An update on that, with a new concern:
This is my pilsner, which went from 1.047 down to 1.011 in 5 days at 54f, at which point I cranked it up to 65f. It's now been having that diacetyl rest for 6 days, which is longer than the first part of the fermentation. I can still taste diacetyl, thought the sulphur quickly went away. Over the last two days, I have detected a new aroma and, to some extent, taste, which seems to be replacing the fresh taste and aroma it at least had a few days ago. It's nothing acetic or sour, more of a meaty (?) smell. Knowing some common descriptors, that would sound like autolysis, though I always see confident advice that we're unlikely to suffer from that in small batches over anything but a very extended period.
There is still a lot of yeast in suspension. I tried a sample from the top, as well as the bottom tap: both showed some diacetyl, to the best of my sensory awareness (popcorn, for me). The bottom sample had more of a tang to it, which I imagine was the higher density of suspended yeast.
SG is now 1.0065, around 86% attenuation, so I guess I'm looking at a pretty thin Pilsner
With the taste getting worse rather than better now, I'm wondering whether to start to lower it for lagering and hope when it clears down it is OK?