Eventually I bought a cheap Tenda Nova MW5c system (a proprietary Realtek chipset-based solution, AFAIK), plugged it in as a replacement for my homebrew OpenWrt-based mesh (in "bridge" mode), and it just works. That's something I haven't been able to achieve with OpenWrt, but I'm not ready to give up just yet
Mesh worked for a while with snapshots on the RT3200, but then stopped working a long time ago. And reports surface now and then confirming the same. Otherwise one sees lots of reports of problems with mesh on various devices on this forum.
It seems mesh doesn't work well in OpenWrt but WDS does. So many of us just use WDS.