Support Nushell as a remote login shell for SSH relay Node.js detection

Problem

Orca SSH relay reports that Node.js is not installed on the remote host, even though node and npm are available on the remote PATH.

The remote user's login shell is Nushell. Since Nushell is not POSIX-compatible, Orca's Node.js detection appears to fail when it probes the remote host with POSIX shell syntax such as command -v node.

This may be related to #5097, but the symptom here is specifically the SSH relay bootstrap failing to detect an existing Node.js runtime.

Environment

• Orca: v1.4.126
• Client OS: Linux / NixOS
• Remote OS: Linux / NixOS
• Remote login shell: Nushell (nu)
• Remote Node.js: v24.14.1
• Remote npm: 11.11.0

Actual behavior

When connecting to the remote host through Orca SSH, the connection fails with:

Error invoking remote method 'ssh:connect': Error: Node.js not found on remote host. Orca relay requires Node.js 18+ and npm.

However, Node.js is present and usable on the remote host.

Reproduction / diagnostic commands

From the client host:

ssh user@remote 'command -v node'

With Nushell as the remote login shell, this fails because command is not a Nushell builtin:

Error: nu::shell::external_command
  x External command failed
   ,- [source:1:1]
 1 | command -v node
   : ^^^|^^^
   :    `-- Command `command` not found

But Node itself is available:

ssh user@remote 'node --version'

v24.14.1

And probing through a POSIX shell works:

ssh user@remote 'sh -lc "command -v node && node --version && command -v npm && npm --version"'

/etc/profiles/per-user/user/bin/node
v24.14.1
/etc/profiles/per-user/user/bin/npm
11.11.0

Expected behavior

Orca should support Nushell as a remote login shell for SSH relay setup and detect Node.js successfully when node and npm are available.

A clearer error message would help, but I think compatibility would be the better outcome here, since Nushell is a reasonable login shell for some users and the runtime itself is already installed.

Possible fix

From a quick look at the current remote Node resolution path, Orca resolves $SHELL and then runs command -v node through that shell. That works for POSIX-like shells and seems to have been improved for zsh/fish in #6037, but Nushell does not support command -v.

One possible approach would be to detect Nushell and use a Nushell-native probe such as which node, then validate the candidate with node --version. Another option may be to run the Node/npm detection through a known POSIX shell when available, while still preserving the existing login-shell behavior for shells where that is needed.

Notes

I can help test a fix on a NixOS remote where the login shell is Nushell and Node.js/npm are installed system-wide.

If you think this is worth supporting, I would also be happy to open a PR and try to implement it.