Make Steam game mode work on a display-less streaming host and stream it at the
client's resolution:
* Ship /etc/gamescope-session-plus/sessions.d/steam (packaging/bazzite/
gamescope-headless-session, installed by the RPM + Arch PKGBUILD): fall back to
gamescope's headless backend when no display is connected, so "Switch to Game
Mode" boots offscreen instead of crashing on the missing panel (and 5-striking
back to desktop). No-op on display-attached boxes; only sets unset values so
the host's per-client mode still wins.
* Default Bazzite/SteamOS to ATTACH (PUNKTFUNK_GAMESCOPE_ATTACH=1 in host.env):
the box owns its session (Desktop<->Game, persistent), the host follows +
captures it and never tears it down — so switching is rock-solid and a
disconnect leaves the box in its mode (reconnect returns there).
* Resize-on-attach (gamescope.rs): on connect, ensure the box's own game-mode
session runs at the CLIENT's resolution — reuse it when already matching (fast
path, no restart), else reconfigure + restart the box's own autologin
gamescope-session-plus@<client> at the client mode (cooperative: no competing
unit, so no autologin-respawn fight). Detect the live gamescope's -W/-H via
argv[0] in /proc (its /proc/<pid>/exe is unreadable for that process).
Validated live on a headless bazzite-deck-nvidia box: game mode boots headless +
stable (0 strikes); the host attaches + streams video/audio/EIS input; a
5120x1440 client reuses the matching session and streams at 5120x1440.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
d9465ad5b6