导出注册表把非 UTF-8 内容归入 malformed

- registry.rs 的 load_or_create 单独处理 ErrorKind::InvalidData，返回 RegistryError::Malformed，不再落进通用 Io 被报成路径/权限故障

- 新增 rejects_non_utf8_content_as_malformed 用例

apps/ai-game-creator-shell/src-tauri/src/export/registry.rs

@@ -72,6 +72,14 @@ where
             write_atomically(path, &created)?;
             (created, true)
         }
+        Err(error) if error.kind() == std::io::ErrorKind::InvalidData => {
+            // 非 UTF-8 字节就是「内容不是本目标期望的形状」，与 JSON 解析失败同类；落进通用 Io 会
+            // 被报成「路径 / 权限故障」，把用户和 agent 往修权限的方向引。
+            return Err(RegistryError::Malformed {
+                path: path.to_path_buf(),
+                cause: format!("注册表不是有效 UTF-8：{error}"),
+            });
+        }
         Err(error) => {
             return Err(RegistryError::Io {
                 path: path.to_path_buf(),
@@ -219,6 +227,21 @@ mod tests {
         assert_eq!(fs::read_to_string(&path).unwrap(), "{ not json");
     }
 
+    #[test]
+    fn rejects_non_utf8_content_as_malformed() {
+        let path = fixture_directory("non-utf8").join("target.json");
+        fs::write(&path, [0xff, 0xfe, 0x00]).unwrap();
+        let empty = Fixture {
+            name: String::new(),
+        };
+
+        let error = load_or_create(&path, &empty).expect_err("invalid utf-8 must fail closed");
+        assert!(
+            matches!(error, RegistryError::Malformed { .. }),
+            "非 UTF-8 必须报成 malformed，而不是 host/path 故障：{error:?}"
+        );
+    }
+
     #[test]
     fn rejects_unknown_fields_so_agent_drift_is_visible() {
         let path = fixture_directory("unknown").join("target.json");