feat(gaming): declarative Proton and dGPU game rendering (#393)

WORKAROUNDS.md

@@ -38,6 +38,7 @@ A setting that works around a bug or a hardware quirk.
 | WA-011 | Kernel module blacklist (`esp4`, `esp6`, `rxrpc`) — `hardening/kernel-hardening.nix`                                      | attack surface for the Dirty Frag LPE (CVE-2026-43284 / CVE-2026-43500) | Kept as defence in depth; drop only if something needs those modules                            | 2026-10-03 | rarely                                      | active |
 | WA-017 | keyd right-hand modifier passthrough — `modules/nixos/desktop/peripherals.nix`                                            | keyd folds right Ctrl/Shift/Meta into their left keys                   | Drop once keyd or fcitx5 keeps right-hand modifiers distinct                                    | 2026-10-05 | on keyd bump                                | active |
 | WA-018 | user-owned `~/.ssh/config` + disabled systemd ssh-proxy include — `home/base/tui/ssh.nix`, `modules/nixos/base/ssh.nix`   | bwrap exposes root-owned store files as `nobody`                        | Drop once sandboxes preserve store ownership                                                    | 2026-10-06 | when sandbox layout changes                 | active |
+| WA-019 | programs.steam.extraCompatPackages = [ pkgs-x64.dwproton-bin pkgs-x64.proton-ge-bin ] — modules/nixos/desktop/gaming.nix  | ACE games fail on GE/mainline Proton, work with DW-Proton               | Drop once mainline or GE-Proton runs these games (GE-Proton#433)                                | 2026-10-07 | on Proton/GE bump                           | active |
 
 If WA-008 freezes recur, the fallback is to restore
 `nvme_core.default_ps_max_latency_us=0 nvme_core.io_timeout=4294967295 pcie_aspm=off`; this is a

hosts/idols-ai/hardware-nvidia.nix

@@ -22,6 +22,17 @@
     nvidiaBusId = "PCI:2@0:0:0";
   };
 
+  # Games launched through GameScope should use the dGPU. prime.offload keeps the
+  # Intel iGPU as the default renderer so the dGPU stays free for LLM workloads,
+  # so opt GameScope games into PRIME render offload here. Games launched outside
+  # GameScope need `nvidia-offload %command%` in their Steam launch options.
+  programs.gamescope.env = {
+    __NV_PRIME_RENDER_OFFLOAD = "1";
+    __NV_PRIME_RENDER_OFFLOAD_PROVIDER = "NVIDIA-G0";
+    __GLX_VENDOR_LIBRARY_NAME = "nvidia";
+    __VK_LAYER_NV_optimus = "NVIDIA_only";
+  };
+
   boot.kernelParams = [
     # Since NVIDIA does not load kernel mode setting by default,
     # enabling it is required to make Wayland compositors function properly.

hosts/idols-ai/preservation.nix

@@ -265,6 +265,7 @@ in
 
         "Games"
         ".steam"
+        ".config/MangoHud"
         ".config/blender"
 
         ".local/share/umu"

modules/nixos/desktop/gaming.nix

@@ -40,10 +40,6 @@ in
       #   ~/.steam             - Some Symlinks & user info
       enable = true;
       package = pkgs-x64.steam;
-      # https://github.com/ValveSoftware/gamescope
-      # Run a GameScope driven Steam session from your display-manager
-      # fix resolution upscaling and stretched aspect ratios
-      gamescopeSession.enable = true;
       # https://github.com/Winetricks/winetricks
       # Whether to enable protontricks, a simple wrapper for running Winetricks commands for Proton-enabled games.
       protontricks.enable = true;
@@ -52,6 +48,26 @@ in
       fontPackages = [
         pkgs.wqy_zenhei # Need by steam for Chinese
       ];
+      # DW-Proton (Dawn Winery's Proton fork) carries the anti-cheat and game
+      # patches that mainline Proton/GE-Proton lack, so it is what runs the anime
+      # gacha games (Wuthering Waves, Honkai: Star Rail, Arknights: Endfield, ...);
+      # GE-Proton is the general fallback. Both appear as compatibility tools in
+      # each game's Properties -> Compatibility.
+      # https://dawn.wine/dawn-winery/dwproton
+      extraCompatPackages = [
+        pkgs-x64.dwproton-bin
+        pkgs-x64.proton-ge-bin
+      ];
+    };
+
+    # GameScope: run a game in its own nested compositor and let it renice
+    # itself for steadier frame pacing. GPU-specific PRIME render offload belongs
+    # to the host, not here (see programs.gamescope.env in
+    # hosts/idols-ai/hardware-nvidia.nix).
+    # https://github.com/ValveSoftware/gamescope
+    programs.gamescope = {
+      enable = true;
+      capSysNice = true;
     };
 
     # see https://github.com/fufexan/nix-gaming/#pipewire-low-latency