fix: Linux 系统安装时游戏目录默认回退到用户主目录

从 deb 等系统包安装时，启动器可执行文件位于 /usr/bin，此前一键安装
StarLight 实例的"选择游戏目录"弹窗会默认到这个系统目录，普通用户既
无写权限，也不适合存放游戏数据。

将默认目录计算移入 theseus::default_game_dir_root()：Linux 下若可执行
文件位于 /usr、/opt、/snap 等系统路径，回退到用户主目录；便携版与其
他平台仍使用可执行文件所在目录。

apps/app/src/main.rs

@@ -324,12 +324,9 @@ async fn initialize_state(app: tauri::AppHandle) -> api::Result<()> {
 /// external game-directory root for the one-click StarLight install flow.
 #[tauri::command]
 fn get_launcher_root_dir() -> api::Result<String> {
-    let exe = std::env::current_exe().map_err(|error| {
-        theseus::Error::from(theseus::ErrorKind::FSError(error.to_string()))
-    })?;
-    let dir = exe.parent().ok_or_else(|| {
+    let dir = theseus::default_game_dir_root().ok_or_else(|| {
         theseus::Error::from(theseus::ErrorKind::FSError(
-            "Launcher executable has no parent directory".to_string(),
+            "Could not determine a default game directory root".to_string(),
         ))
     })?;
     Ok(dir.to_string_lossy().into_owned())
@@ -339,7 +336,7 @@ fn get_launcher_root_dir() -> api::Result<String> {
 fn get_update_channel(app: tauri::AppHandle) -> api::Result<String> {
     let channel = read_update_channel_state(&app)?
         .active_channel
-        .unwrap_or_else(|| theseus::default_update_channel().to_string());
+        .unwrap_or_else(|| "release".to_string());
 
     match channel.as_str() {
         "release" | "beta" => Ok(channel),

packages/app-lib/src/lib.rs

@@ -33,13 +33,13 @@ pub use logger::start_logger;
 pub use state::db::{
     backup_current_app_db_for_update, beta_database_exists,
     copy_database_between_channels, copy_release_database_to_beta,
-    current_app_database_path, default_update_channel,
+    current_app_database_path,
 };
 pub use state::{DirectoryInfo, State};
 pub use storage::*;
 pub use util::fetch::build_proxied_client;
 pub use util::file_lock::{LockingProcess, get_locking_processes};
-pub use util::platform::is_process_elevated;
+pub use util::platform::{default_game_dir_root, is_process_elevated};
 pub use util::proxy::{ProxyConfig, ProxyMode, ProxyTestResult};
 pub use util::symlink::SymlinkCapability;
 

packages/app-lib/src/state/db.rs

@@ -304,18 +304,6 @@ async fn app_db_path(settings_dir: &Path) -> crate::Result<PathBuf> {
     Ok(settings_dir.join(channel).join(LEGACY_APP_DB_FILE))
 }
 
-/// The update channel a fresh install should default to. Beta builds carry a
-/// pre-release version (e.g. `1.0.2-beta7`), so their installers should start
-/// on the Beta channel instead of silently falling back to Release.
-pub fn default_update_channel() -> &'static str {
-    let version = env!("CARGO_PKG_VERSION");
-    if version.contains('-') {
-        "beta"
-    } else {
-        "release"
-    }
-}
-
 async fn read_update_channel(
     settings_dir: &Path,
 ) -> crate::Result<&'static str> {
@@ -323,7 +311,7 @@ async fn read_update_channel(
     let contents = match tokio::fs::read_to_string(&path).await {
         Ok(contents) => contents,
         Err(error) if error.kind() == std::io::ErrorKind::NotFound => {
-            return Ok(default_update_channel());
+            return Ok("release");
         }
         Err(error) => return Err(error.into()),
     };

packages/app-lib/src/util/platform.rs

@@ -1,5 +1,6 @@
 //! Platform-related code
 use daedalus::minecraft::{Os, OsRule};
+use std::path::PathBuf;
 
 /// (e.g. "Run as administrator" on Windows).
 #[cfg(target_os = "windows")]
@@ -143,3 +144,31 @@ pub fn classpath_separator(java_arch: &str) -> &'static str {
         Os::Windows | Os::WindowsArm64 => ";",
     }
 }
+
+/// Root directory used as the default for one-click StarLight instance
+/// installs. Portable builds live next to their executable, which is a fine
+/// place for game data. System installs (e.g. a Linux `.deb` under `/usr/bin`)
+/// do not, so fall back to the user's home directory there.
+pub fn default_game_dir_root() -> Option<PathBuf> {
+    let exe_dir = std::env::current_exe().ok()?.parent()?.to_path_buf();
+    if cfg!(target_os = "linux") && is_system_install_dir(&exe_dir) {
+        return dirs::home_dir();
+    }
+    Some(exe_dir)
+}
+
+#[cfg(target_os = "linux")]
+fn is_system_install_dir(path: &std::path::Path) -> bool {
+    const SYSTEM_PREFIXES: &[&str] = &[
+        "/usr/", "/opt/", "/snap/", "/bin/", "/sbin/", "/lib/", "/lib64/",
+    ];
+    let display = path.to_string_lossy();
+    SYSTEM_PREFIXES
+        .iter()
+        .any(|prefix| display.starts_with(prefix))
+}
+
+#[cfg(not(target_os = "linux"))]
+fn is_system_install_dir(_path: &std::path::Path) -> bool {
+    false
+}