Feature/feishu receive file (#1608)

* feat(feishu): add channel file materialization hook for inbound messages

- Introduce Channel.receive_file(msg, thread_id) as a base method for file materialization; default is no-op.
- Implement FeishuChannel.receive_file to download files/images from Feishu messages, save to sandbox, and inject virtual paths into msg.text.
- Update ChannelManager to call receive_file for any channel if msg.files is present, enabling downstream model access to user-uploaded files.
- No impact on Slack/Telegram or other channels (they inherit the default no-op).

* style(backend): format code with ruff for lint compliance

- Auto-formatted packages/harness/deerflow/agents/factory.py and tests/test_create_deerflow_agent.py using `ruff format`
- Ensured both files conform to project linting standards
- Fixes CI lint check failures caused by code style issues

* fix(feishu): handle file write operation asynchronously to prevent blocking

* fix(feishu): rename GetMessageResourceRequest to _GetMessageResourceRequest and remove redundant code

* test(feishu): add tests for receive_file method and placeholder replacement

* fix(manager): remove unnecessary type casting for channel retrieval

* fix(feishu): update logging messages to reflect resource handling instead of image

* fix(feishu): sanitize filename by replacing invalid characters in file uploads

* fix(feishu): improve filename sanitization and reorder image key handling in message processing

* fix(feishu): add thread lock to prevent filename conflicts during file downloads

* fix(test): correct bad merge in test_feishu_parser.py

* chore: run ruff and apply formatting cleanup
fix(feishu): preserve rich-text attachment order and improve fallback filename handling

backend/tests/test_channel_file_attachments.py

@@ -276,6 +276,31 @@ class _DummyChannel(Channel):
 
 
 class TestBaseChannelOnOutbound:
+    def test_default_receive_file_returns_original_message(self):
+        """The base Channel.receive_file returns the original message unchanged."""
+
+        class MinimalChannel(Channel):
+            async def start(self):
+                pass
+
+            async def stop(self):
+                pass
+
+            async def send(self, msg):
+                pass
+
+        from app.channels.message_bus import InboundMessage
+
+        bus = MessageBus()
+        ch = MinimalChannel(name="minimal", bus=bus, config={})
+        msg = InboundMessage(channel_name="minimal", chat_id="c1", user_id="u1", text="hello", files=[{"file_key": "k1"}])
+
+        result = _run(ch.receive_file(msg, "thread-1"))
+
+        assert result is msg
+        assert result.text == "hello"
+        assert result.files == [{"file_key": "k1"}]
+
     def test_send_file_called_for_each_attachment(self, tmp_path):
         """_on_outbound sends text first, then uploads each attachment."""
         bus = MessageBus()