nix-config/.agents/skills/nix-config-umu-game/SKILL.md

name, description

name	description
nix-config-umu-game	Use when installing a Windows game launcher (二次元 / gacha or any non-Steam game) on a NixOS desktop via umu-launcher, given an installer URL or an .exe, when such a launcher opens an invisible, transparent, black, or empty window under Wine, or when its download crawls behind the proxy.

Installing a Windows game launcher with umu

The bundled scripts/umu-install.nu renders the files in scripts/templates/. It creates a prefix, runs the installer, and writes launchers. Use the Nix DW-Proton default unless research identifies a specific installed release; then select it with PROTONPATH and pin that path in the game's conf. Every per-game detail lives under ~/Gaming/Games/, never in this repo.

The sandbox

Games run only inside the umu nixpak sandbox (hardening/nixpaks/umu.nix, policy in hardening/nixpaks/modules/gaming-policy.nix). It mounts ~/Gaming over $HOME; no other host file is visible or writable. umu-run, winetricks, bbe, mangohud and gamescope exist only inside it, and umu-sandbox <command> runs a command there.

Two views of one path: ~/Gaming/<path> on the host is ~/<path> in the sandbox, so a game lives at ~/Gaming/Games/<name> on the host and at ~/Games/<name> inside. The host has no ~/Games: a path written that way is a sandbox path. Typed after umu-sandbox in a host shell, ~/Games/<name>/run expands to exactly that sandbox path. Host environment variables do not reach the sandbox; put them in conf.

Everything under ~/Gaming is writable by the games, so the host never executes a file from it:

• launch with umu-sandbox ~/Games/<name>/run and use umu-sandbox ~/Games/<name>/exec ...; the generated desktop entry does the former. Running run or exec directly refuses to start.
• the installer and prelaunch also run through umu-sandbox;
• umu-install.nu refuses to write through a symlink in the game directory, and uninstalling uses the repo's umu-uninstall.nu, not a script in ~/Gaming.

Bundled files

• scripts/umu-install.nu: installer and template renderer
• scripts/umu-uninstall.nu: removes a game's desktop entry and, after confirmation, its directory
• scripts/common.nu: name, symlink and sandbox-path helpers shared by both
• scripts/templates/*.tpl: non-executable templates; placeholders use @NAME@
• scripts/tests/test_install.py: offline regression tests

Layout

Host paths; inside the sandbox drop the Gaming/.

• ~/Gaming: the sandbox's $HOME, shared with the other game launchers (umu runtime, Steam, Heroic, saves written to $HOME)
• ~/Gaming/Games/global.conf: optional, sourced by every game before its own conf
• ~/Gaming/Games/<name>/prefix: the Wine prefix (WINEPREFIX)
• ~/Gaming/Games/<name>/conf: optional per-game overrides (ENABLE_MANGOHUD=0, ...)
• ~/Gaming/Games/<name>/prelaunch: optional executable, run before every launch
• ~/Gaming/Games/<name>/run: generated launcher
• ~/Gaming/Games/<name>/exec: generated helper: umu-sandbox ~/Games/<name>/exec <exe-or-tool>
• ~/Gaming/Games/<name>/<name>.desktop: generated desktop entry

Run, from the repo root:

nu .agents/skills/nix-config-umu-game/scripts/umu-install.nu <name> <setup.exe> <launcher> [gameid] [setup-args...]

<launcher> is relative to the prefix and GAMEID defaults to umu-default. A <setup.exe> outside ~/Gaming is copied into the game directory first; - skips the installer and only rewrites run, exec and the desktop entry. At install, PROTONPATH resolves from $PROTONPATH, $UMU_PROTONPATH (the Nix-provided DW-Proton), then Steam's per-user compatibilitytools.d in the sandbox home; it must be a store path or under ~/Gaming. run, exec and the desktop entry hold sandbox paths. At launch, the generated run script checks the current $PROTONPATH and $UMU_PROTONPATH before its saved default. A game's conf is sourced after those defaults, so set PROTONPATH there to pin a particular installed version across launches.

Procedure

1. Research first. Mandatory before inventing any fix: a documented fix beats a custom patch every time. Check the game's Lutris installer YAML as data only (https://lutris.net/api/installers/<game-slug> encodes winetricks verbs, write_file content, and prelaunch_command; do not install or run Lutris), then ProtonDB (protondb.com/app/<id>), Steam Community / r/linux_gaming threads, and GitHub issues for the launcher and Proton. Record whether reports require a Proton family and exact release. If no exact release is required, use the Nix-provided DW-Proton default. If one is required, inspect $UMU_PROTONPATH, the Nix GE-Proton (nix build --no-link --print-out-paths .#nixosConfigurations.<host>.pkgs.proton-ge-bin.steamcompattool) and installed Steam tools under ~/Gaming/.local/share/Steam/compatibilitytools.d/ (the sandbox's ~/.local/share/Steam/compatibilitytools.d/); select the matching installed path with PROTONPATH. Prefix the installer command with PROTONPATH="<selected-tool-directory>" and set the same value in the game's conf to pin it across launches; otherwise the runtime Nix UMU_PROTONPATH may take precedence. If the required release is absent from Nix and Steam, stop and ask the user before downloading it from elsewhere. Do not substitute a different release or use ProtonPlus/Lutris to fetch one: a host-side downloader writes outside ~/Gaming, where the sandbox cannot see it, and a store path cannot be modified by a game.
2. Slug. Pick a lowercase <name> (e.g. wuthering-waves).
3. GAMEID. The umu database maps a title to a GAMEID whose protonfixes add CJK fonts, drop the SteamOS/SteamDeck vars, and keep Wine's Documents inside the prefix. Without it some games save into the host home or the wrong prefix. Fetch https://raw.githubusercontent.com/Open-Wine-Components/umu-database/main/umu-database.csv, match the title, and use its umu-<id>; if nothing matches, leave the default.
4. Download. curl -fL <url> -o ~/Gaming/Games/<name>/setup.exe. The CN store pages are JS/token driven, so the user normally supplies the URL or the file itself.
5. Install. Run the bundled script. The first run also downloads umu's Steam runtime and the protonfix fonts, so it is slow. The installer is usually a GUI the user clicks through, but extra args after [gameid] go to setup.exe, so try a silent flag first (/S, /quiet, --silent); if it ignores them, fall back to clicking. On some CN installers the last page auto-starts the launcher. The script writes run/exec even if the installer exits non-zero, so a killed installer is not fatal.
6. Find the launcher. If <launcher> is only known after install, locate it under ~/Gaming/Games/<name>/prefix/drive_c and set LAUNCHER in ~/Gaming/Games/<name>/conf. Re-running the installer script invokes setup.exe again; only do so if that installer is known to handle reruns.
7. Per-game fix. Port step 1 findings into ~/Gaming/Games/<name>/prelaunch (bash, chmod +x): winetricks verbs via ~/Games/<name>/exec winetricks <verbs>, file patches or registry tweaks via ~/Games/<name>/exec. prelaunch runs in the sandbox, so it uses sandbox paths and calls exec directly; from a host shell, prefix it with umu-sandbox. Never commit the fix to this repo.
8. Re-run every launch, not once. A launcher that self-updates overwrites files it patches, so those patches belong in prelaunch.
9. Verify. umu-sandbox ~/Games/<name>/run must open a visible launcher window. MangoHud is enabled by default with FPS and frame time at the top-left; set ENABLE_MANGOHUD=0 in conf to disable it, or override MANGOHUD_CONFIG. Re-running prelaunch must be idempotent. The launcher may then download the game body itself (tens of GB) -- that is the launcher's job, not this skill's, so the install is done once the window is usable. A crawl usually means the proxy: the launcher probes the CDN itself and mihomo routes that probe through a distant node, so the download starts from a far mirror; routing is in the mihomo README. ENABLE_LOG=1 captures last-run.log when something misbehaves.

Invisible / transparent launcher window

A WebView2/.NET (WPF) launcher that shows an empty or fully transparent window is rendering with AllowsTransparency. Fix the DLL, not Wine:

1. find ~/Gaming/Games/<name>/prefix/drive_c -iname 'launcher_main.dll' (usually under a X.Y.Z.W version dir).
2. Rename that WPF property in place, keeping the byte length so PE offsets stay valid: bbe -e 's/\x12AllowsTransparency/\x09IsEnabled\x1bA\x00\x03AAAAA/' <dll>. bbe exists only in the sandbox: prefix it with umu-sandbox from a host shell.
3. Put it in ~/Gaming/Games/<name>/prelaunch so it is re-applied on every launch, because a launcher self-update restores the original DLL. Restart the launcher after patching.

Half-width tile instead of fullscreen

Niri tiles a new window into a column of default-column-width { proportion 0.500000; } (50%), and a launcher that only opens a large borderless window cannot take over the screen by itself: with a 4K panel at scale 1.5 Niri's logical space is 2560x1440, so a window asking for the physical 3840x2160 becomes an ordinary half-width tile. Nothing is broken -- the umu app-id is just not covered by a rule.

Every umu/Proton game reports steam_app_<GAMEID>. In this repo home/linux/gui/niri/conf/windowrules.kdl matches app-id="^steam_app_[0-9]+$" and sets open-fullscreen true, so games open fullscreen without a per-game rule. niri validate checks the live config, Mod+Shift+F (fullscreen-window) toggles an already-open window, and setting the in-game resolution to the compositor's logical size (2560x1440 here) avoids the mismatch too.

A launcher shares that app id with its game, so the rule also catches the launcher's own windows: a helper that is still untitled while it maps, and the announcement popup (公告 / Announcement), which on this launcher renders as a pure white rectangle. Fullscreening either one buries the UI that opened it, so both are excluded. A window rule applies when a window opens, so an already-open offender needs Mod+Shift+F on it or a relaunch; drop open-fullscreen true altogether if a launcher keeps surprising you -- the game then costs one Mod+Shift+F per session instead.

Mojibake that is not a missing font

Latin-looking garbage such as 我已阅读 where the launcher should say 我已阅读并同意, while other Chinese on the same window renders fine, is UTF-8 decoded as Windows-1252. Confirm the pattern:

python3 -c "print('我已阅读并同意'.encode('utf-8').decode('cp1252','replace'))"

If that prints exactly what the launcher shows, the bug is identified and you can stop here.

The string itself is fine and so are the fonts: the same launcher renders 请输入手机号 and 登录 correctly, and the garbled label exists as correct UTF-16 in KRSDKEx.dll. The bytes are simply decoded with a single-byte Western codepage.

This is not the prefix locale. Setting LANG=zh_CN.UTF-8 in ~/Gaming/Games/<name>/conf does change the prefix (verified in this repo: "ACP" went 1252 -> 936 and "LocaleName" en-US -> zh-CN), and the garbling stayed byte-for-byte identical. The launcher decodes those bytes as Latin-1 no matter what Windows codepage it is told to use, so this is an upstream bug in its own text pipeline: report it, or accept it -- the launcher still works. LANG is nevertheless the lever for the prefix locale, not LC_ALL: Proton clears LC_ALL unless HOST_LC_ALL is set.

So: check the bytes first, do not install more CJK fonts, and do not promise a locale fix.

Silent install

umu-install.nu <name> <setup.exe> <launcher> <gameid> /S passes /S to the installer. Not all installers honour it; try /quiet or --silent too, then fall back to the GUI.

Desktop entry and persistence

The script also writes ~/.local/share/applications/<name>.desktop (and a copy at ~/Gaming/Games/<name>/<name>.desktop), so the game shows up in the desktop launcher. The host copy is written by the installer on the host; the sandbox cannot see or change it. Under an impermanence setup both ~/Gaming and ~/.local/share/applications must be in the host's preservation.preserveAt list, in hosts/<dir>/preservation.nix.

Uninstall

From the repo root:

nu .agents/skills/nix-config-umu-game/scripts/umu-uninstall.nu <name>

It removes the desktop entry and then asks before deleting ~/Gaming/Games/<name> (prefix + game files). To keep the game and only drop the menu entry, delete the .desktop file by hand.

Games installed before the sandbox

Move ~/Games to ~/Gaming/Games and the old ~/.local/share/umu to ~/Gaming/.local/share/umu (on the same filesystem, so both are renames; umu can also download its runtime again). Paths inside the game directories stay valid, because the sandbox sees them at the old ~/Games/<name>. The old desktop entries execute run on the host, and an old uninstall script is host-executed too, so rewrite the launchers without re-running the installer, passing the LAUNCHER and GAMEID from the old run:

nu .agents/skills/nix-config-umu-game/scripts/umu-install.nu <name> - <launcher> <gameid>

This also deletes the old uninstall.

Optimize the launch

~/Gaming/Games/<name>/conf (or ~/Gaming/Games/global.conf) is a shell file the generated run sources. Defaults are ENABLE_MANGOHUD=1, MANGOHUD_CONFIG="fps=1,frametime=1,position=top-left", ENABLE_GAMEMODE=0, ENABLE_GAMESCOPE=0, GAMESCOPE_ARGS="-f", and ENABLE_LOG=0. Set ENABLE_MANGOHUD=0 to hide the overlay, ENABLE_GAMESCOPE=1 + GAMESCOPE_ARGS="-f -w 3840 -h 2160" for the handheld / multi-monitor case, and ENABLE_LOG=1 to capture the run. Gamescope runs inside the sandbox without CAP_SYS_NICE, so it cannot raise its own priority. ENABLE_GAMEMODE=1 has no effect: gamemoderun is not in the sandbox, whose PID namespace and D-Bus filter keep gamemoded from managing the game. A host wrapper such as nvidia-offload does not work either, because the sandbox clears the environment; export its variables (__NV_PRIME_RENDER_OFFLOAD=1, ...) in conf instead. Shader caches are kept in ~/Gaming/Games/<name>/shader-cache.

Escape hatches

• umu-sandbox ~/Games/<name>/exec <exe-or-tool> [args...] runs anything in the prefix with the right env: an absolute path to a game exe or repair tool, or a bare Wine tool (winecfg, explorer, regedit, uninstaller), which it runs as umu-run <Proton's wine> <tool>. Both forms are handed to umu-run, so they execute inside umu's Steam runtime container -- that is what makes them work on a non-FHS distro like NixOS, where Proton's wine cannot start on its own.
• umu-sandbox ~/Games/<name>/run <game args> passes extra args to the launcher.
• Kill a stuck prefix with pkill -f '/Games/<name>/prefix', or rm -f ~/Gaming/Games/<name>/prefix/pfx.lock.

Common mistakes

• Launching again while the first launch after a Proton update or a moved umu runtime shows no window: it is preparing steamrt4 and upgrading the prefix, which can take a minute, and a second launch blocks on the same locks. Wait, or pkill -f '/Games/<name>/prefix' and launch once.
• Committing a game name, URL, or patch to this repo instead of ~/Gaming/Games/<name>/.
• Patching once instead of in prelaunch -- the next launcher self-update undoes it.
• Dropping the GAMEID -- the in-game CJK fonts and the save location go wrong.
• Installing more CJK fonts when the text is mojibake -- decode the bytes first (see above).
• Expecting umu to fetch DW-Proton: it only auto-manages GE-Proton / UMU-Proton; use Nix or Steam installed paths. Ask the user before obtaining a required release from elsewhere.
• Running a Wine tool without umu. umu-run winecfg does not work -- umu only special-cases winetricks -- and $PROTONPATH/files/bin/wine winecfg fails on any non-FHS distro (on NixOS the 32-bit loader it needs lives only inside the Steam runtime container). Use umu-sandbox ~/Games/<name>/exec winecfg; exec goes through umu-run, which provides that container.
• Running run, exec or prelaunch from a host shell, or adding a host-side helper that executes a file under ~/Gaming: games can rewrite those files. Go through umu-sandbox.
• Pointing PROTONPATH, a launcher or an installer at a host path outside ~/Gaming: the sandbox cannot see it. Inside conf and prelaunch, write sandbox paths (~/Games/<name>).
• Waiting for the game download before calling the install done: the launcher's own download is out of scope here.
• On NixOS a game needing 32-bit or Vulkan needs hardware.graphics.enable32Bit, and Steam is a module rather than a package: modules/nixos/desktop/gaming.nix.

Regression tests

From the repo root:

python3 .agents/skills/nix-config-umu-game/scripts/tests/test_install.py

Requires python3, nu, bash, and shellcheck. Uses temporary homes and stub umu-run and umu-sandbox; no game downloads, Wine windows, or changes to existing games. It checks template permissions, rendered shell syntax and lint, installer arguments and failures, configuration precedence, prelaunch, logging, launch wrappers, literal paths, runtime Proton overrides, tool routing, uninstall confirmation, the sandbox guard, host-to-sandbox path translation, and refusal to write through planted symlinks.