diff --git a/apps/ai-game-creator-shell/src-tauri/src/commands.rs b/apps/ai-game-creator-shell/src-tauri/src/commands.rs
index d8dd83cae..e97c894a1 100644
--- a/apps/ai-game-creator-shell/src-tauri/src/commands.rs
+++ b/apps/ai-game-creator-shell/src-tauri/src/commands.rs
@@ -5399,3 +5399,47 @@ pub(crate) fn write_project_permission_policy(
     let _lock = acquire_project_write_lock(root, "project.policy_write")?;
     write_project_permission_policy_at(root, policy)
 }
+
+#[cfg(test)]
+mod custom_directory_tests {
+    use super::create_local_project_directory;
+    use std::fs;
+
+    #[test]
+    fn creates_child_directory_without_touching_parent_contents() {
+        let root = tempfile::tempdir().expect("temp parent");
+        let created = create_local_project_directory(
+            root.path().to_string_lossy().into_owned(),
+            "new-game".to_string(),
+        )
+        .expect("create directory");
+        let path = std::path::PathBuf::from(created);
+        assert!(path.is_dir());
+        assert!(fs::read_dir(root.path())
+            .expect("read parent")
+            .next()
+            .is_some());
+    }
+
+    #[test]
+    fn rejects_existing_child_and_path_separator() {
+        let root = tempfile::tempdir().expect("temp parent");
+        fs::create_dir(root.path().join("existing")).expect("existing");
+        assert_eq!(
+            create_local_project_directory(
+                root.path().to_string_lossy().into_owned(),
+                "existing".to_string(),
+            )
+            .expect_err("duplicate must fail"),
+            "目录已存在"
+        );
+        assert_eq!(
+            create_local_project_directory(
+                root.path().to_string_lossy().into_owned(),
+                "nested/name".to_string(),
+            )
+            .expect_err("separator must fail"),
+            "目录名称无效"
+        );
+    }
+}