Abuse unison's -sshcmd option to synchronize with the VM on WSL without sshd.

example.bat

> unison C:\unison-test ssh://user@localhost/unison-test -retry 0 -repeat watch -sshcmd C:\\double\\backslashes\\path\\to\\wsl-as-ssh.cmd

wsl-as-ssh.cmd

@echo off

set "USER_NAME="
rem ESCAPE_CHAR perhaps isn't helpful for WSL
rem set "ESCAPE_CHAR="
rem PORT perhaps isn't helpful for WSL
rem set "PORT="
set "HOST_NAME="
set "COMMAND="

:PARSE_ARGS
if "%~1"=="" goto :END_PARSE_ARGS

if "%~1"=="-l" (
  set "USER_NAME=%~2"
  shift
) else if "%~1"=="-p" (
  rem set "PORT=%~2"
  shift
) else if "%~1"=="-e" (
  rem set "ESCAPE_CHAR=%~2"
  shift
) else (
  if not defined HOST_NAME (
    set "HOST_NAME=%~1"
  ) else (
    set "COMMAND=%COMMAND% %~1"
  )
)

shift
goto :PARSE_ARGS

:END_PARSE_ARGS


wsl --cd "~" -u %USER_NAME% -- %COMMAND%

NOTE: Most of the wsl-as-ssh.cmd is written by ChatGPT (GPT 3.5).