修正 CI 权限用例在 root 容器下的前提并补平台无关的分类判据

- project_write_lock_does_not_project_permission_denial_as_contention 不再用 expect_err 断言“只读目录必须挡住取锁”：CI 容器以 root 运行，0o500 不生效，取锁会正常成功；此时跳过端到端前提
- 新增平台无关用例 project_write_lock_classifies_by_whether_the_target_exists：目标存在才是争用、目标不存在却创建失败是权限拒绝、NotFound 归其它
- 让权限分类判据在不依赖 ACL 环境的条件下也有回归护栏，避免只靠会被 root 绕过的端到端用例

apps/ai-game-creator-shell/src-tauri/src/project/filesystem.rs

@@ -485,6 +485,33 @@ fn project_write_lock_reports_acl_denial_without_an_existing_target() {
     );
 }
 
+/// 分类判据本身与平台无关，两个平台都要盯住：目标存在才是争用，目标不存在却创建失败
+/// 是权限拒绝。这条用例不依赖 ACL 环境，因此在 CI 容器以 root 运行时仍然有效。
+#[test]
+fn project_write_lock_classifies_by_whether_the_target_exists() {
+    assert_eq!(
+        project_write_lock_classify_open_error(
+            &std::io::Error::from(std::io::ErrorKind::AlreadyExists),
+            true
+        ),
+        ProjectWriteLockOpenFailure::Contention
+    );
+    assert_eq!(
+        project_write_lock_classify_open_error(
+            &std::io::Error::from(std::io::ErrorKind::PermissionDenied),
+            false
+        ),
+        ProjectWriteLockOpenFailure::Permission
+    );
+    assert_eq!(
+        project_write_lock_classify_open_error(
+            &std::io::Error::from(std::io::ErrorKind::NotFound),
+            false
+        ),
+        ProjectWriteLockOpenFailure::Other
+    );
+}
+
 #[cfg(all(test, windows))]
 #[test]
 fn project_write_lock_hardens_space_containing_path_in_process() {

apps/ai-game-creator-shell/src-tauri/src/tests/project_lock_recovery.rs

@@ -426,10 +426,15 @@ fn project_write_lock_does_not_project_permission_denial_as_contention() {
     fs::set_permissions(&agent_directory, fs::Permissions::from_mode(0o500))
         .expect("去掉控制目录写权限");
 
-    let error =
-        acquire_project_write_lock(&root, "file.write").expect_err("只读控制目录必须挡住取锁");
+    let outcome = acquire_project_write_lock(&root, "file.write");
     fs::set_permissions(&agent_directory, original).expect("恢复控制目录权限");
 
+    // CI 容器以 root 运行，0o500 目录照样可以创建文件；此时本用例的前提不成立，
+    // 直接跳过。分类判据本身另有不依赖 ACL 环境的纯函数用例覆盖。
+    let Err(error) = outcome else {
+        return;
+    };
+
     assert!(
         !error.starts_with("项目正在被其他写操作占用："),
         "权限拒绝不得投影成写锁争用：{error}"