Add FUSE external mapping support, BG3/Oblivion Remastered fixes, fomod-plus and NaK integration

FUSE VFS now deploys non-data-dir mod mappings (Paks, OBSE, UE4SS, etc.)
via real symlinks and injects file-level data-dir mappings (plugins.txt,
loadorder.txt) into the VFS tree. Fixes game launches for Oblivion
Remastered (Root Builder path resolution, script extender support) and
BG3 (Wine prefix documents directory, file mapper symlinks on Linux).

Vendors mo2-fomod-plus plugin and NaK crate for FOMOD installer and
game finder/runtime support.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 135 insertions, 0 deletions

diff --git a/libs/nak/src/steam/mod.rs b/libs/nak/src/steam/mod.rs
new file mode 100644
index 0000000..c5964aa
--- /dev/null
+++ b/libs/nak/src/steam/mod.rs
@@ -0,0 +1,135 @@
+//! Steam integration module
+//!
+//! Handles Proton detection, Steam path detection, and mount point discovery.
+//! Shortcuts and config.vdf manipulation removed (handled by C++ side).
+
+mod paths;
+mod proton;
+
+// Re-export path detection utilities
+pub use paths::{
+    detect_steam_path_checked, find_steam_path, find_userdata_path,
+    get_steam_accounts,
+};
+
+// Re-export Proton detection
+pub use proton::{find_steam_protons, SteamProton};
+
+use std::fs;
+
+/// Kill Steam process gracefully, then force if needed
+pub fn kill_steam() -> Result<(), Box<dyn std::error::Error>> {
+    use std::process::Command;
+
+    // Try steam -shutdown first (graceful)
+    let _ = Command::new("steam")
+        .arg("-shutdown")
+        .status();
+
+    std::thread::sleep(std::time::Duration::from_secs(2));
+
+    // Then force kill if still running
+    let _ = Command::new("pkill")
+        .arg("-9")
+        .arg("steam")
+        .status();
+
+    // Brief wait for Steam to fully exit
+    std::thread::sleep(std::time::Duration::from_secs(2));
+
+    Ok(())
+}
+
+/// Start Steam in background
+pub fn start_steam() -> Result<(), Box<dyn std::error::Error>> {
+    use std::process::{Command, Stdio};
+
+    Command::new("setsid")
+        .arg("steam")
+        .arg("-silent")
+        .stdout(Stdio::null())
+        .stderr(Stdio::null())
+        .spawn()?;
+
+    Ok(())
+}
+
+/// Restart Steam (kill then start)
+pub fn restart_steam() -> Result<(), Box<dyn std::error::Error>> {
+    kill_steam()?;
+    start_steam()?;
+    Ok(())
+}
+
+// ============================================================================
+// STEAM_COMPAT_MOUNTS Detection
+// ============================================================================
+
+/// Directories that pressure-vessel already exposes by default
+const ALREADY_EXPOSED: &[&str] = &[
+    "bin", "etc", "home", "lib", "lib32", "lib64",
+    "overrides", "run", "sbin", "tmp", "usr", "var",
+];
+
+/// System directories that shouldn't be mounted
+const SYSTEM_DIRS: &[&str] = &[
+    "proc", "sys", "dev", "boot", "root", "lost+found", "snap",
+];
+
+/// Detect directories at root that need to be added to STEAM_COMPAT_MOUNTS
+pub fn detect_extra_mounts() -> Vec<String> {
+    let mut mounts = Vec::new();
+
+    let Ok(entries) = fs::read_dir("/") else {
+        return mounts;
+    };
+
+    for entry in entries.flatten() {
+        let name = entry.file_name().to_string_lossy().to_string();
+
+        if ALREADY_EXPOSED.contains(&name.as_str()) {
+            continue;
+        }
+
+        if SYSTEM_DIRS.contains(&name.as_str()) {
+            continue;
+        }
+
+        if name.starts_with('.') {
+            continue;
+        }
+
+        if entry.path().is_dir() {
+            mounts.push(format!("/{}", name));
+        }
+    }
+
+    mounts.sort();
+    mounts
+}
+
+/// Generate launch options string with DXVK config file and STEAM_COMPAT_MOUNTS
+pub fn generate_launch_options(dxvk_conf_path: Option<&std::path::Path>, is_electron_app: bool) -> String {
+    let mounts = detect_extra_mounts();
+
+    let dxvk_part = match dxvk_conf_path {
+        Some(path) => format!(
+            "DXVK_CONFIG_FILE=\"{}\"",
+            crate::config::normalize_path_for_steam(&path.to_string_lossy())
+        ),
+        None => String::new(),
+    };
+
+    let electron_flags = if is_electron_app {
+        " --disable-gpu --no-sandbox"
+    } else {
+        ""
+    };
+
+    match (dxvk_part.is_empty(), mounts.is_empty()) {
+        (true, true) => format!("%command%{}", electron_flags),
+        (true, false) => format!("STEAM_COMPAT_MOUNTS={} %command%{}", mounts.join(":"), electron_flags),
+        (false, true) => format!("{} %command%{}", dxvk_part, electron_flags),
+        (false, false) => format!("{} STEAM_COMPAT_MOUNTS={} %command%{}", dxvk_part, mounts.join(":"), electron_flags),
+    }
+}