Answer appears to be: RAS-only.
With system in memory error (or halted in ODT prompt) I'm seeing a 200 ns /RAS every 14.67 us, /CAS staying high.
As 14.67 us * 256 = 3.75 ms, this looks like RAS-only refresh doing the 256 refreshes within the 4 ms required period and otherwise idle for RAM.