My last update on getting Bonjour/mDNS working on my network ended with “If it ain’t broke”… Sadly, the broke state cropped up at some point between then and now. Home sharing with the Apple TV was no longer working, and nothing had changed on my end to break it. Apple may have changed things on their end, breaking stuff, but regardless of the cause, my network wasn’t working right.
Fortunately, the fine people on the EdgeOS boards had already fixed this, amusingly enough even before my earlier attempts to get it working right. Instead of using mDNS reflector, using mDNS repeater apparently works much better. Specifically, following the instructions here fixed things nicely. Until the next time something breaks, that is…