Handling of process exit is still broken. It detects the moment when the
child process exits, then quickly stops polling for process output. It
should continue polling for output until the agent has scraped all of the
process' output. This problem is easy to notice by running a command like
"dir && exit", but even typing "exit<ENTER>" can manifest the problem --
the "t" might not appear.
winpty's Cygwin adapter handles shutdown by waiting for the agent to close
the CONOUT pipe, which it does after it has scraped the child's last
output. AFAIK, neovim doesn't do anything interesting when winpty closes
the CONOUT pipe.
