From 96dbbb3cbe7d8a9f695c3bc0bf7006367d1181a4 Mon Sep 17 00:00:00 2001
From: Erich Blume <725328+eblume@users.noreply.github.com>
Date: Fri, 15 May 2026 12:11:54 -0700
Subject: [PATCH] C0: add sn2-prelaunch wrapper to clear SN2 stale lockfiles
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UE5 writes Saved/running.dat as a "session in progress" marker. If
the previous session exited uncleanly (SIGKILL, crash), it lingers,
and SN2 pops up an invisible 0×0 Error dialog at next launch that
the GameThread blocks on forever — visible only as a black screen
with a spinning loader. Wrap the Steam command to clear the marker
files before each launch.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 .../+ringtail-sn2-prelaunch.infra.md            |  6 ++++++
 nixos/ringtail/gaming.nix                       | 17 +++++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 docs/changelog.d/+ringtail-sn2-prelaunch.infra.md

diff --git a/docs/changelog.d/+ringtail-sn2-prelaunch.infra.md b/docs/changelog.d/+ringtail-sn2-prelaunch.infra.md
new file mode 100644
index 0000000..f9c68e2
--- /dev/null
+++ b/docs/changelog.d/+ringtail-sn2-prelaunch.infra.md
@@ -0,0 +1,6 @@
+Add `sn2-prelaunch` Steam launch wrapper on ringtail that removes
+Subnautica 2's stale `Saved/running.dat` and `Saved/beforelobby.dat`
+lockfiles before each launch. SN2 pops up an invisible (0×0-sized)
+Error dialog when it detects an unclean exit, blocking GameThread
+forever; this is observable only as a black screen with a spinning
+loader. Use via Steam launch option: `sn2-prelaunch %command%`.
diff --git a/nixos/ringtail/gaming.nix b/nixos/ringtail/gaming.nix
index c526857..7c00378 100644
--- a/nixos/ringtail/gaming.nix
+++ b/nixos/ringtail/gaming.nix
@@ -13,6 +13,23 @@
   # so disable xalia globally to avoid wedging iscriptevaluator.exe.
   environment.sessionVariables.PROTON_USE_XALIA = "0";
 
+  # Subnautica 2 pre-launch wrapper. SN2 (UE5) writes Saved/running.dat as a
+  # "currently running" lockfile. If the prior session exited uncleanly (SIGKILL
+  # via Steam's Stop button, crash, etc.), the file persists and on next launch
+  # SN2 pops up an invisible (0x0-sized) Error dialog ("Your game might not have
+  # exited correctly last time...") that the GameThread blocks on forever —
+  # observable only as a black screen with a spinning loader. This wrapper
+  # removes the stale lockfiles before exec'ing the actual game command.
+  # Use as Steam launch option for Subnautica 2:
+  #   sn2-prelaunch %command%
+  environment.systemPackages = [
+    (pkgs.writeShellScriptBin "sn2-prelaunch" ''
+      saved="/mnt/games/SteamLibrary/steamapps/compatdata/1962700/pfx/drive_c/users/steamuser/AppData/Local/Subnautica2/Saved"
+      rm -f "$saved/running.dat" "$saved/beforelobby.dat"
+      exec "$@"
+    '')
+  ];
+
   # Gamescope — micro-compositor for game fullscreen/resolution management.
   # Use as Steam launch option: gamescope -W 2560 -H 1440 -f -- %command%
   programs.gamescope = {