diff --git a/app/service/offsite_document_recognition_adapter.py b/app/service/offsite_document_recognition_adapter.py
index 0b4970f..4b3b9e2 100644
--- a/app/service/offsite_document_recognition_adapter.py
+++ b/app/service/offsite_document_recognition_adapter.py
@@ -785,7 +785,8 @@ def _confidence_map(value: Mapping[str, object]) -> dict[str, Decimal]:
 
 def _document_type(value: object) -> DocumentType:
     if value in ("summary", "subscription", "redemption", "other"):
-        return cast(DocumentType, value)
+        # 不需要 cast：上面的 `in (...)` 已经把类型收窄到那个字面量联合了。
+        return value
     return "other"
 
 
diff --git a/app/service/offsite_fund_service.py b/app/service/offsite_fund_service.py
index 09daee3..4e37973 100644
--- a/app/service/offsite_fund_service.py
+++ b/app/service/offsite_fund_service.py
@@ -7,7 +7,7 @@ from datetime import UTC, date, datetime
 from decimal import Decimal
 from email import policy
 from email.header import decode_header, make_header
-from email.message import Message
+from email.message import EmailMessage
 from email.parser import BytesParser
 from email.utils import parsedate_to_datetime
 from pathlib import Path
@@ -1190,7 +1190,10 @@ class OffsiteFundService:
 
     @staticmethod
     def _parse_eml(path: str) -> dict[str, object]:
-        empty = {
+        # 显式标注：字面量里只有一个 bool，mypy 会把它推断成 `dict[str, bool | None]`，
+        # 而 dict 是**不变型**，`dict[str, bool | None]` 不是 `dict[str, object]` 的子类型。
+        # 运行时本来就是合法值，缺的只是这一个标注。
+        empty: dict[str, object] = {
             "subject": None,
             "sent_at": None,
             "has_body": False,
@@ -1227,8 +1230,11 @@ class OffsiteFundService:
         except (LookupError, UnicodeError, ValueError):
             return value
 
+    # 形参标注用 EmailMessage 而不是基类 Message：`get_content()` 只定义在 EmailMessage 上，
+    # 而调用方传的是 `BytesParser(policy=policy.default).parsebytes(...)` 的返回值 ——
+    # 它本来就是 EmailMessage。原先标注成基类，mypy 于是在下面报"没有该属性"。
     @staticmethod
-    def _mail_body(message: Message) -> tuple[str | None, str | None]:
+    def _mail_body(message: EmailMessage) -> tuple[str | None, str | None]:
         text_body: str | None = None
         html_body: str | None = None
         parts = message.walk() if message.is_multipart() else (message,)