ssh with multiplexing fails after connection and leaves zombie ssh processes

[Jim Garrison]

I just learned about ssh multiplexing and tried to set it up (Cygwin 
client to Debian server), but it fails to work and each attempt leaves a 
zombie ssh process.

According to the ssh -vvv debug output, authentication is successful but 
then fails during setup of the control master with

     mm_receive_fd: no message header
     mux_master_process_new_session: failed to receive fd 0 from client

I found a StackOverflow post from over a decade ago indicating the 
problem is that Cygwin doesn't support file descriptor passing via 
unix-domain sockets.  https://stackoverflow.com/questions/20959792

Is it still true that ssh multiplexing is not available in Cygwin, or is 
there a way to make it work?

-- 
Jim Garrison
jhg@acm.org