remote SSH: respect `VSCODE_SERVER_*` env vars

As I mentioned in https://github.com/posit-dev/positron/discussions/8234#discussioncomment-13554296, our open-remote-ssh extension does not seem to be providing certain environment variables to the server script. It would be helpful to pass along VSCODE_SERVER_* env vars, which could power use cases like below.

Discussed in https://github.com/posit-dev/positron/discussions/8234

^{Originally posted by KGZaker June 22, 2025}
First, thank you so much for maintaining Positron—it’s been a huge help!

Background:
I’m trying to use Positron’s SSH feature to connect to an HPC cluster running Ubuntu 18.04, but out of the box neither Positron nor VS Code’s Remote–SSH work on that older distro. Following the instructions here: can-i-run-vs-code-server-on-older-linux-distributions, I configured a sysroot and patchelf. After that, I can successfully connect to the Ubuntu 18.04 host from the latest VS Code via the built-in Remote–SSH extension. However, Positron still fails to connect via SSH.

Expected Behavior:
Maybe Positron can leverage the same patched server approach (or an equivalent workaround) to establish an SSH‐Remote session on Ubuntu 18.04 HPC hosts.

Questions:
Are there alternative methods you’d recommend for getting Positron’s SSH support working on older Linux distributions?

Any guidance would be much appreciated! Thank you again for your work on Positron.

Start with the open-remote-ssh extension and its server script launch path, then review the linked discussion for the expected older-Linux SSH use case. Trace how environment variables are passed to the server script; done means the relevant VSCODE_SERVER_* variables reach the remote server session.