Windows: remote PC connect hangs because Windows OpenSSH never exits when spawned headless #1944

Summary

On a Windows PC, connecting a saved herdr machine (a macOS host) never finishes. The "Checking the remote environment…" step runs until the 90 s ssh.run timeout. The cause is Windows OpenSSH: when ssh.exe is spawned headless the way the server spawns it (Bun.spawn, stdin: "ignore", piped stdout/stderr, under the detached + windowsHide server), the remote command completes and its output arrives, but ssh.exe never exits.

Environment

• Ovis 0.4.16 (herdr plugin), herdr 0.9.3 on Windows 11 (10.0.26200), PowerShell 7.6
• Windows OpenSSH client OpenSSH_for_Windows_9.5p2 (System32). The portable 10.4.0.0p1-Preview build behaves the same.
• Remote: macOS, herdr 0.9.5. Plain ssh host cmd from an interactive terminal works.

What I observed

Process trace of one Connect click (children of the Ovis server process):

• ssh … -T host exit (the proof): exits after about 1 s
• ssh … -N -T host: stays up, as expected
• ssh … -T host "sh -c '…uname -s…'" (posixHost.inspect): never exits. The job then falls back to the PowerShell probe and fails.

Minimal reproduction (outside Ovis)

Run this from a headless context, e.g. a non-tty ssh windows-pc 'bun test.ts':

for (const cmd of ["exit", "echo hi", "echo hi >&2"]) {
  const proc = Bun.spawn(["ssh", "-o", "BatchMode=yes", "-T", "mac-host", cmd], { stdin: "ignore", stdout: "pipe", stderr: "pipe" });
  const timer = setTimeout(() => proc.kill(), 8000);
  const [out, , code] = await Promise.all([new Response(proc.stdout).text(), new Response(proc.stderr).text(), proc.exited]);
  clearTimeout(timer);
  console.log(cmd, code, JSON.stringify(out));
}

-n, -E logfile, -o LogLevel=QUIET, -tt, and a file as stdin do not help. Any byte written by the remote command is enough to trigger the hang. The upstream Win32-OpenSSH report closest to this is PowerShell/Win32-OpenSSH#2448.

Workaround in use

I copied Git for Windows' ssh.exe, ssh-keygen.exe, sftp.exe and their msys-*.dll (plus etc/nsswitch.conf) into a folder placed first on the system PATH. With that, the same probes return in about 0.2 s.

Suggestion

On Windows, allow overriding the client binary (e.g. OVIS_SSH, plus ssh-keygen/sftp), or prefer Git for Windows' ssh when it is installed. Alternatively, spawn ssh.exe with a console attached.