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, 257 insertions, 0 deletions

diff --git a/libs/nak/src/steam/proton.rs b/libs/nak/src/steam/proton.rs
new file mode 100644
index 0000000..064fd96
--- /dev/null
+++ b/libs/nak/src/steam/proton.rs
@@ -0,0 +1,257 @@
+//! Steam Proton detection and management
+//!
+//! Finds Protons that Steam can see and use for non-Steam games.
+//! This includes Steam's built-in Protons and custom Protons in compatibilitytools.d.
+
+use std::fs;
+use std::path::PathBuf;
+
+use super::find_steam_path;
+
+/// Information about an installed Proton version
+#[derive(Debug, Clone)]
+pub struct SteamProton {
+    /// Display name (e.g., "GE-Proton9-20", "Proton Experimental")
+    pub name: String,
+    /// Internal name used in config.vdf (e.g., "proton_experimental", "GE-Proton9-20")
+    pub config_name: String,
+    /// Full path to the Proton installation
+    pub path: PathBuf,
+    /// Whether this is a Steam-provided Proton (vs custom)
+    pub is_steam_proton: bool,
+    /// Whether this is Proton Experimental
+    pub is_experimental: bool,
+}
+
+impl SteamProton {
+    /// Get the path to the wine binary.
+    pub fn wine_binary(&self) -> Option<PathBuf> {
+        let paths = [
+            self.path.join("files/bin/wine"),
+            self.path.join("dist/bin/wine"),
+        ];
+        paths.into_iter().find(|p| p.exists())
+    }
+
+    /// Get the path to the wineserver binary.
+    pub fn wineserver_binary(&self) -> Option<PathBuf> {
+        let paths = [
+            self.path.join("files/bin/wineserver"),
+            self.path.join("dist/bin/wineserver"),
+        ];
+        paths.into_iter().find(|p| p.exists())
+    }
+
+    /// Get the bin directory containing wine executables.
+    pub fn bin_dir(&self) -> Option<PathBuf> {
+        self.wine_binary().and_then(|p| p.parent().map(|p| p.to_path_buf()))
+    }
+}
+
+/// Find all Protons that Steam can use (Proton 10+ only)
+pub fn find_steam_protons() -> Vec<SteamProton> {
+    let mut protons = Vec::new();
+
+    let Some(steam_path) = find_steam_path() else {
+        return protons;
+    };
+
+    let is_flatpak = steam_path.to_string_lossy().contains(".var/app/com.valvesoftware.Steam");
+
+    // 1. Steam's built-in Protons (steamapps/common/Proton*)
+    protons.extend(find_builtin_protons(&steam_path));
+
+    // 2. Custom Protons in user's compatibilitytools.d
+    protons.extend(find_custom_protons(&steam_path));
+
+    // 3. System-level Protons in /usr/share/steam/compatibilitytools.d/
+    if is_flatpak {
+        crate::logging::log_info("Flatpak Steam detected - skipping system protons in /usr/share/steam/compatibilitytools.d/");
+    } else {
+        protons.extend(find_system_protons());
+    }
+
+    // Filter to only include Proton 10+ (required for Steam-native integration)
+    protons.retain(is_proton_10_or_newer);
+
+    // Filter to only include Protons with valid wine binaries
+    protons.retain(|p| {
+        let has_wine = p.wine_binary().is_some();
+        if !has_wine {
+            crate::logging::log_warning(&format!(
+                "Skipping Proton '{}': wine binary not found at expected paths (files/bin/wine or dist/bin/wine)",
+                p.name
+            ));
+        }
+        has_wine
+    });
+
+    // Sort: Experimental first, then by name descending (newest first)
+    protons.sort_by(|a, b| {
+        if a.is_experimental != b.is_experimental {
+            return b.is_experimental.cmp(&a.is_experimental);
+        }
+        b.name.cmp(&a.name)
+    });
+
+    protons
+}
+
+/// Check if a Proton version is 10 or newer
+fn is_proton_10_or_newer(proton: &SteamProton) -> bool {
+    let name = &proton.name;
+
+    if proton.is_experimental || name.contains("Experimental") {
+        return true;
+    }
+
+    if name.contains("CachyOS") {
+        return true;
+    }
+
+    if name == "LegacyRuntime" || name.contains("Runtime") {
+        return false;
+    }
+
+    if name.starts_with("GE-Proton") {
+        if let Some(version_part) = name.strip_prefix("GE-Proton") {
+            let major: Option<u32> = version_part
+                .split('-')
+                .next()
+                .and_then(|s| s.parse().ok());
+            return major.map(|v| v >= 10).unwrap_or(false);
+        }
+    }
+
+    if name.starts_with("Proton ") {
+        if let Some(version_part) = name.strip_prefix("Proton ") {
+            let major: Option<u32> = version_part
+                .split('.')
+                .next()
+                .and_then(|s| s.parse().ok());
+            return major.map(|v| v >= 10).unwrap_or(false);
+        }
+    }
+
+    if name.starts_with("EM-") {
+        if let Some(version_part) = name.strip_prefix("EM-") {
+            let major: Option<u32> = version_part
+                .split('.')
+                .next()
+                .and_then(|s| s.parse().ok());
+            return major.map(|v| v >= 10).unwrap_or(false);
+        }
+    }
+
+    // Unknown format - allow it
+    true
+}
+
+/// Find Steam's built-in Proton versions
+fn find_builtin_protons(steam_path: &std::path::Path) -> Vec<SteamProton> {
+    let mut found = Vec::new();
+    let common_dir = steam_path.join("steamapps/common");
+
+    let Ok(entries) = fs::read_dir(&common_dir) else {
+        return found;
+    };
+
+    for entry in entries.flatten() {
+        let path = entry.path();
+        if !path.is_dir() {
+            continue;
+        }
+
+        let name = entry.file_name().to_string_lossy().to_string();
+
+        if name.starts_with("Proton") && path.join("proton").exists() {
+            let is_experimental = name.contains("Experimental");
+
+            let config_name = if is_experimental {
+                "proton_experimental".to_string()
+            } else {
+                let version = name.replace("Proton ", "");
+                let major = version.split('.').next().unwrap_or(&version);
+                format!("proton_{}", major)
+            };
+
+            found.push(SteamProton {
+                name: name.clone(),
+                config_name,
+                path,
+                is_steam_proton: true,
+                is_experimental,
+            });
+        }
+    }
+
+    found
+}
+
+/// Find custom Protons in compatibilitytools.d
+fn find_custom_protons(steam_path: &std::path::Path) -> Vec<SteamProton> {
+    let mut found = Vec::new();
+    let compat_dir = steam_path.join("compatibilitytools.d");
+
+    let Ok(entries) = fs::read_dir(&compat_dir) else {
+        return found;
+    };
+
+    for entry in entries.flatten() {
+        let path = entry.path();
+        if !path.is_dir() {
+            continue;
+        }
+
+        let name = entry.file_name().to_string_lossy().to_string();
+
+        let has_proton = path.join("proton").exists();
+        let has_vdf = path.join("compatibilitytool.vdf").exists();
+
+        if has_proton || has_vdf {
+            found.push(SteamProton {
+                name: name.clone(),
+                config_name: name.clone(),
+                path,
+                is_steam_proton: false,
+                is_experimental: false,
+            });
+        }
+    }
+
+    found
+}
+
+/// Find system-level Protons in /usr/share/steam/compatibilitytools.d/
+fn find_system_protons() -> Vec<SteamProton> {
+    let mut found = Vec::new();
+    let system_compat_dir = PathBuf::from("/usr/share/steam/compatibilitytools.d");
+
+    let Ok(entries) = fs::read_dir(&system_compat_dir) else {
+        return found;
+    };
+
+    for entry in entries.flatten() {
+        let path = entry.path();
+        if !path.is_dir() {
+            continue;
+        }
+
+        let name = entry.file_name().to_string_lossy().to_string();
+
+        let has_proton = path.join("proton").exists();
+        let has_vdf = path.join("compatibilitytool.vdf").exists();
+
+        if has_proton || has_vdf {
+            found.push(SteamProton {
+                name: name.clone(),
+                config_name: name.clone(),
+                path,
+                is_steam_proton: false,
+                is_experimental: false,
+            });
+        }
+    }
+
+    found
+}