If this XDG_RUNTIME_DIR is supported on most posix platforms we may look at this

again.

In particular, $XDG_RUNTIME_DIR only allows writing by the user, so if you want
to have a socket with a fixed name and no random component, you can safely do that.

Hence my followup correcting that to $XDG_RUNTIME_DIR, which if set points to a
user-specific writable directory intended for this kind of purpose (sockets and
other runtime files for user-specific daemons).

Correction: this directory should move to $XDG_RUNTIME_DIR (if set).