I didn’t recompile at all, just installed the distributed .ipk (and didn’t allow it to (re-)create the .conf file either, so that would have been identical to what was working with the previous nightly).
After the restart and NOT rescanning that I mentioned earlier, I streamed an album (192k MP3 files, totally vanilla stuff) to my Roku Soundbridge and it went well for the first few tracks then Firefly stopped sending anything to the soundbridge; just stopped playback and the library wasn’t browsable anymore on there. The Firefly web interface was still working, so the processes on the NSLU2 were still up, just it wasn’t available in a useful way.
I have now uninstalled and gone back to the previous Firefly nightly (svn-1463) and fully rescanned using that (deleted the database and config file and did a total clean install of 1463). That version had been running for about a month continuously with no problems at all, including several rescans, serving the same Soundbridge, so I might stay back on that version for a while for spouse-compatibility reasons.