Interesting features of this spin are that it’s 2.0mm thickness (still a little thin but operational), and two-sided (thanks to Passerby for circuit tip).
There are two bugs. One, the board was too wide. I forgot to resize it after removing the metal connector from the layout. So I filed down the edges around the USB connector, and it’s fine. Two, part of the top ground plane got disconnected from the rest, so the left LED’s ground is floating. Weirdly enough, it works fine, except that it can’t communicate reliably with the right LED, so the right LED flickers. A bodge wire fixed that, and if I manufacture any more from this batch of boards, I think I can run that wire underneath the LED assemblies.
Except for the two errors, which are now fixed in the latest layout, I think this version could be the one that gets produced at scale.