calloop surfaces the closed-socket condition either as
Error::IoError(BrokenPipe) — already handled — or as
Error::OtherError wrapping an std::io::Error with kind BrokenPipe,
which previously fell through to panic!(). Add a matching arm that
downcasts the inner error and treats both forms the same: log and
set exit_requested so the run loop terminates gracefully instead
of unwinding.
