69e2003f

By: ananjiani <ananjiani@noreply.codeberg.org>

fix(steammachine): expose Proton GE to Gaming Mode (#355)

## Summary

```text
programs.steam.extraCompatPackages
  → steamcompattool output paths
  → jovian.steam.environment
  → Gaming Mode Steam
```

Gaming Mode and Desktop Mode both run as `ammar`. Jovian's launcher bypasses the NixOS Steam wrapper that exposes extra compatibility tools. Pass the existing package list to `STEAM_EXTRA_COMPAT_TOOLS_PATHS` in the gamescope session environment.

Steam Machine only. No separate package list, pinned GE version, Steam configuration edits, or Steam Deck changes.

## Evidence

- **Before:** live Gaming Mode Steam has `USER=ammar`, `HOME=/home/ammar`, no `STEAM_EXTRA_COMPAT_TOOLS_PATHS`; `compatibilitytools.d` contains only `LegacyRuntime`.
- **After:** targeted evaluation exports the configured GE `steamcompattool` output in `/etc/xdg/gamescope-session/environment`. The generated path retains its Nix store reference.
- nixfmt, statix, deadnix and `git diff --check` pass. Independent GPT-6.1 Sol review found no static blockers.
- CI owns all builds. Runtime inheritance and the Gaming Mode compatibility menu still need a check after deployment.

## Merge Danger

**Door:** two-way. Restore the previous generation to undo the change.

**Blast Radius:** Gaming Mode.

A full Gaming Mode session restart is needed to load the changed environment. Do not restart during a game. No Steam license, manifest, or shortcut edits.

Co-authored-by: Ammar <ammar.nanjiani@gmail.com>
Reviewed-on: https://codeberg.org/ananjiani/infra/pulls/355

Total

17m00s

Timeline