wisp.place answers 400 Invalid path to any path with an empty segment, so the /manage/at://… addresses the page writes broke as soon as they were reloaded or shared. This writes them as /manage/at:/<repo>/dev.blinkers.lens/<rkey>/ instead, which wisp serves (I checked with curl) and the page already parsed.
A real at:// uri pasted straight into the address bar will still get wisp's 400; there's nothing the page can do about that one.