Catch piping errors not working

[gregk]

What do you use registers for?

Looks like user registers can preserve shell return codes when piping into buffers. e.g, |junk;echo "evaluate-commands "“reg a “”$?”>$kak_command_fifo then :<c-r>a :echo %sh{echo $kak_reg_a} should both show 127

It would be nice to be able to write :echo %sh{junk; echo $?>$kak_reg_a}
but Kakoune registers seem to be read only from the shell. Does anyone know why?