It seems Evolution 2.32 moved its email files from ~/.evolution/mail/local (where I previously tweaked their location) to ~/.local/share/evolution/mail. As a result, Evolution fired up with all its various options and accounts still in place, but with a completely default set of folders.
After considerable thrashing around, all that’s required is a simple:
cd ~/.local/share/evolution mv local local.base ln -s /NFS-mounted-directory/Mail local
And it all works again.
This actually happened in 2.31.6, but the Arch Linux version jumped from 2.30.3 to 2.32.0 in one fell swoop. Some version of the Evolution changelogs are there, but the money quote is:
Evolution 2.31.6 2010-08-02 --------------------------- Evolution now complies with the XDG Base Directory Specification , which means user-specific data is no longer stored under ~/.evolution. Instead, data is partitioned into three base directories controlled by environment variables: $XDG_DATA_HOME/evolution (default: $HOME/.local/share/evolution) $XDG_CACHE_HOME/evolution (default: $HOME/.cache/evolution) $XDG_CONFIG_HOME/evolution (default: $HOME/.config/evolution) Data which is managed by Evolution will be migrated from $HOME/.evolution on startup.  http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
I think the “migration” tripped over the symlink I used to aim just the mail folder to the NFS mount.
One could argue that such a wrenching change should get some advance warning, but …