feat: Enhance chat streaming and tool call processing (#498)

* feat: Enhance chat streaming and tool call processing

- Added support for MongoDB checkpointer in the chat streaming workflow.
- Introduced functions to process tool call chunks and sanitize arguments.
- Improved event message creation with additional metadata.
- Enhanced error handling for JSON serialization in event messages.
- Updated the frontend to convert escaped characters in tool call arguments.
- Refactored the workflow input preparation and initial message processing.
- Added new dependencies for MongoDB integration and tool argument sanitization.

* fix: Update MongoDB checkpointer configuration to use LANGGRAPH_CHECKPOINT_DB_URL

* feat: Add support for Postgres checkpointing and update README with database recommendations

* feat: Implement checkpoint saver functionality and update MongoDB connection handling

* refactor: Improve code formatting and readability in app.py and json_utils.py

* refactor: Clean up commented code and improve formatting in server.py

* refactor: Remove unused imports and improve code organization in app.py

* refactor: Improve code organization and remove unnecessary comments in app.py

* chore: use langgraph-checkpoint-postgres==2.0.21 to avoid the JSON convert issue in the latest version, implement chat stream persistant with Postgres

* feat: add MongoDB and PostgreSQL support for LangGraph checkpointing, enhance environment variable handling

* fix: update comments for clarity on Windows event loop policy

* chore: remove empty code changes in MongoDB and PostgreSQL checkpoint tests

* chore: clean up unused imports and code in checkpoint-related files

* chore: remove empty code changes in test_checkpoint.py

* chore: remove empty code changes in test_checkpoint.py

* chore: remove empty code changes in test_checkpoint.py

* test: update status code assertions in MCP endpoint tests to allow for 403 responses

* test: update MCP endpoint tests to assert specific status codes and enable MCP server configuration

* chore: remove unnecessary environment variables from unittest workflow

* fix: invert condition for MCP server configuration check to raise 403 when disabled

* chore: remove pymongo from test dependencies in uv.lock

* chore:  optimize the _get_agent_name method

* test: enhance ChatStreamManager tests for PostgreSQL and MongoDB initialization

* test: add persistence tests for ChatStreamManager with PostgreSQL and MongoDB

* test: add unit tests for ChatStreamManager initialization with PostgreSQL and MongoDB

* test: enhance persistence tests for ChatStreamManager with PostgreSQL and MongoDB to verify message aggregation

* test: add unit tests for ChatStreamManager with PostgreSQL and MongoDB

* test: add unit tests for ChatStreamManager initialization with PostgreSQL and MongoDB

* test: add unit tests for ChatStreamManager initialization with PostgreSQL and MongoDB

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

server.py

@@ -4,7 +4,8 @@
 """
 Server script for running the DeerFlow API.
 """
-
+import os
+import asyncio
 import argparse
 import logging
 import signal
@@ -19,6 +20,17 @@ logging.basicConfig(
 
 logger = logging.getLogger(__name__)
 
+# To ensure compatibility with Windows event loop issues when using Uvicorn and Asyncio Checkpointer,
+# This is necessary because some libraries expect a selector-based event loop.
+# This is a workaround for issues with Uvicorn and Watchdog on Windows.
+# See:
+# Since Python 3.8 the default on Windows is the Proactor event loop,
+# which lacks add_reader/add_writer and can break libraries that expect selector-based I/O (e.g., some Uvicorn/Watchdog/stdio integrations).
+# For compatibility, this forces the selector loop.
+if os.name == "nt":
+    logger.info("Setting Windows event loop policy for asyncio")
+    asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())
+
 
 def handle_shutdown(signum, frame):
     """Handle graceful shutdown on SIGTERM/SIGINT"""