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/app/channels/base.py

@@ -106,3 +106,21 @@ class Channel(ABC):
                         logger.warning("[%s] file upload skipped for %s", self.name, attachment.filename)
                 except Exception:
                     logger.exception("[%s] failed to upload file %s", self.name, attachment.filename)
+
+    async def receive_file(self, msg: InboundMessage, thread_id: str) -> InboundMessage:
+        """
+        Optionally process and materialize inbound file attachments for this channel.
+
+        By default, this method does nothing and simply returns the original message.
+        Subclasses (e.g. FeishuChannel) may override this to download files (images, documents, etc)
+        referenced in msg.files, save them to the sandbox, and update msg.text to include
+        the sandbox file paths for downstream model consumption.
+
+        Args:
+            msg: The inbound message, possibly containing file metadata in msg.files.
+            thread_id: The resolved DeerFlow thread ID for sandbox path context.
+
+        Returns:
+            The (possibly modified) InboundMessage, with text and/or files updated as needed.
+        """
+        return msg