fix: fall back to sh for remote path discovery

refs #1201

src/remote/unix.rs

@@ -842,6 +842,16 @@ fn remote_binary_on_path_any(
     remote_herdr: &RemoteHerdr,
 ) -> io::Result<Option<RemoteHerdr>> {
     let output = ssh.user_shell_output("command -v herdr")?;
+    if output.status.success() {
+        let stdout = String::from_utf8_lossy(&output.stdout);
+        if let Some(candidate) = remote_herdr_from_path_discovery(remote_herdr, &stdout) {
+            return Ok(Some(candidate));
+        }
+    }
+
+    // Non-POSIX login shells such as xonsh reject `command -v`; retry through
+    // /bin/sh while retaining the login-shell probe for shell-initialized PATHs.
+    let output = ssh.sh_output("command -v herdr\n")?;
     if !output.status.success() {
         return Ok(None);
     }