注册表错误带上底层错误并实现 source

export/registry.rs：新增 RegistryErrorCause，io/serde 失败保留原始错误类型（拿不到类型时用 Message 兜底），RegistryError 与 Cause 都实现 std::error::Error::source，Display 文案不变。
export/draft/xhs_minitool/error.rs：只在命令边界把 cause 转成 String，配合新增测试锁定 io::ErrorKind 可透出。

apps/ai-game-creator-shell/src-tauri/src/export/draft/xhs_minitool/error.rs

@@ -192,7 +192,9 @@ macro_rules! impl_from_registry_error {
             fn from(error: crate::export::RegistryError) -> Self {
                 match error {
                     crate::export::RegistryError::Malformed { cause, .. } => {
-                        Self::RegistryMalformed(RegistryMalformed { cause })
+                        Self::RegistryMalformed(RegistryMalformed {
+                            cause: cause.to_string(),
+                        })
                     }
                     other => Self::ExportUnavailable(ExportUnavailable::new(other.to_string())),
                 }

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

@@ -24,15 +24,103 @@ pub(crate) struct Loaded<T> {
     pub(crate) created: bool,
 }
 
+/// 注册表失败的底层现场。
+///
+/// 能拿到底层错误类型时（`io` / `serde`）就把类型带出来，这样 Rust 侧调用方可以按
+/// `std::io::ErrorKind` 或 serde 错误分流，日志也能沿 `source()` 追到根因；只有本模块自己拼
+/// 出来的一句话（例如「注册表路径缺少父目录」）才退化成 [`RegistryErrorCause::Message`]。
+/// `context` 是给原始错误补的中文说明，只影响展示，不影响类型。
+#[derive(Debug)]
+pub(crate) enum RegistryErrorCause {
+    Io {
+        context: Option<&'static str>,
+        error: std::io::Error,
+    },
+    Serde {
+        context: Option<&'static str>,
+        error: serde_json::Error,
+    },
+    Message(String),
+}
+
+impl RegistryErrorCause {
+    fn message(message: impl Into<String>) -> Self {
+        Self::Message(message.into())
+    }
+
+    fn io(error: std::io::Error) -> Self {
+        Self::Io {
+            context: None,
+            error,
+        }
+    }
+
+    fn io_with_context(context: &'static str, error: std::io::Error) -> Self {
+        Self::Io {
+            context: Some(context),
+            error,
+        }
+    }
+
+    fn serde(error: serde_json::Error) -> Self {
+        Self::Serde {
+            context: None,
+            error,
+        }
+    }
+}
+
+impl fmt::Display for RegistryErrorCause {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Io { context, error } => match context {
+                Some(context) => write!(formatter, "{context}：{error}"),
+                None => write!(formatter, "{error}"),
+            },
+            Self::Serde { context, error } => match context {
+                Some(context) => write!(formatter, "{context}：{error}"),
+                None => write!(formatter, "{error}"),
+            },
+            Self::Message(message) => formatter.write_str(message),
+        }
+    }
+}
+
+impl std::error::Error for RegistryErrorCause {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::Io { error, .. } => Some(error),
+            Self::Serde { error, .. } => Some(error),
+            Self::Message(_) => None,
+        }
+    }
+}
+
 /// 注册表文件级失败。目标模块负责把它映射成自己的 typed error。
 #[derive(Debug)]
 pub(crate) enum RegistryError {
     /// 路径不可读写（含父目录创建失败）。
-    Io { path: PathBuf, cause: String },
+    Io {
+        path: PathBuf,
+        cause: RegistryErrorCause,
+    },
     /// 文件内容不是本目标期望的形状。fail closed：不猜测、不修补。
-    Malformed { path: PathBuf, cause: String },
+    Malformed {
+        path: PathBuf,
+        cause: RegistryErrorCause,
+    },
     /// 宿主自己的 DTO 序列化失败，属于编程错误。
-    Encode { cause: String },
+    Encode { cause: RegistryErrorCause },
+}
+
+impl std::error::Error for RegistryError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::Io { cause, .. } | Self::Malformed { cause, .. } | Self::Encode { cause } => {
+                Some(cause)
+            }
+        }
+    }
 }
 
 impl fmt::Display for RegistryError {
@@ -83,13 +171,13 @@ where
             // 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}"),
+                cause: RegistryErrorCause::io_with_context("注册表不是有效 UTF-8", error),
             });
         }
         Err(error) => {
             return Err(RegistryError::Io {
                 path: path.to_path_buf(),
-                cause: error.to_string(),
+                cause: RegistryErrorCause::io(error),
             });
         }
     };
@@ -111,7 +199,7 @@ pub(crate) fn save<T: Serialize>(path: &Path, value: &T) -> Result<String, Regis
 /// 规范形式：两空格缩进 + 结尾换行。agent 会手改这个文件，人类可读比紧凑更重要。
 fn encode<T: Serialize>(value: &T) -> Result<String, RegistryError> {
     let mut text = serde_json::to_string_pretty(value).map_err(|error| RegistryError::Encode {
-        cause: error.to_string(),
+        cause: RegistryErrorCause::serde(error),
     })?;
     text.push('\n');
     Ok(text)
@@ -120,7 +208,7 @@ fn encode<T: Serialize>(value: &T) -> Result<String, RegistryError> {
 fn decode<T: DeserializeOwned>(path: &Path, text: &str) -> Result<T, RegistryError> {
     serde_json::from_str(text).map_err(|error| RegistryError::Malformed {
         path: path.to_path_buf(),
-        cause: error.to_string(),
+        cause: RegistryErrorCause::serde(error),
     })
 }
 
@@ -131,11 +219,11 @@ fn decode<T: DeserializeOwned>(path: &Path, text: &str) -> Result<T, RegistryErr
 fn write_atomically(path: &Path, text: &str) -> Result<(), RegistryError> {
     let parent = path.parent().ok_or_else(|| RegistryError::Io {
         path: path.to_path_buf(),
-        cause: "注册表路径缺少父目录".to_string(),
+        cause: RegistryErrorCause::message("注册表路径缺少父目录"),
     })?;
     fs::create_dir_all(parent).map_err(|error| RegistryError::Io {
         path: path.to_path_buf(),
-        cause: format!("创建导出目录失败：{error}"),
+        cause: RegistryErrorCause::io_with_context("创建导出目录失败", error),
     })?;
     let temp = temp_path(path);
     let write = || -> std::io::Result<()> {
@@ -153,14 +241,14 @@ fn write_atomically(path: &Path, text: &str) -> Result<(), RegistryError> {
         let _ = fs::remove_file(&temp);
         return Err(RegistryError::Io {
             path: path.to_path_buf(),
-            cause: error.to_string(),
+            cause: RegistryErrorCause::io(error),
         });
     }
     fs::rename(&temp, path).map_err(|error| {
         let _ = fs::remove_file(&temp);
         RegistryError::Io {
             path: path.to_path_buf(),
-            cause: error.to_string(),
+            cause: RegistryErrorCause::io(error),
         }
     })?;
     // rename 只改目录条目：不 fsync 父目录的话，崩溃后「哪个文件才是新的」这件事可能没落盘，
@@ -292,4 +380,24 @@ mod tests {
         assert_eq!(loaded.value, value);
         assert_eq!(loaded.content_hash, hash);
     }
+
+    #[test]
+    fn error_keeps_the_underlying_io_kind_for_rust_callers() {
+        let error = RegistryError::Io {
+            path: PathBuf::from("/tmp/registry.json"),
+            cause: RegistryErrorCause::io_with_context(
+                "创建导出目录失败",
+                std::io::Error::from(std::io::ErrorKind::PermissionDenied),
+            ),
+        };
+
+        // 展示文案保持原样，Rust 侧则能沿 source() 一路拿回 io::Error 并按 ErrorKind 分流。
+        assert!(error.to_string().contains("创建导出目录失败"));
+        let cause = std::error::Error::source(&error).expect("cause");
+        let io = cause
+            .source()
+            .and_then(|source| source.downcast_ref::<std::io::Error>())
+            .expect("io source");
+        assert_eq!(io.kind(), std::io::ErrorKind::PermissionDenied);
+    }
 }