fix: enhance message deserialization to prevent MESSAGE_COERCION_FAIL…

[bsbodden]

…URE (#85)

• Add comprehensive error handling and recovery in _deserialize_channel_values
• Enhance _recursive_deserialize with detailed error messages for debugging
• Document the message serialization/deserialization process extensively
• Add tests to verify proper handling of LangChain message objects
• Ensure messages stored in serialized format are properly reconstructed

The issue occurred when messages were stored in LangChain's serialized format with 'lc', 'type', 'constructor' fields but not properly deserialized back to message objects, causing errors when the application expected objects with 'role' and 'content' attributes.

This fix ensures robust handling of message serialization/deserialization with proper error recovery and detailed logging for debugging.

[Copilot]

Pull Request Overview

This PR fixes the MESSAGE_COERCION_FAILURE issue that occurs when using streaming with subgraphs, where messages stored in LangChain's serialized format fail to deserialize properly on subsequent requests with the same thread_id. The fix enhances message deserialization with comprehensive error handling and recovery mechanisms.

• Add robust error handling and recovery in message deserialization methods
• Enhance the JsonPlusRedisSerializer with proper LangChain object reconstruction
• Add comprehensive documentation explaining the message serialization/deserialization process

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
tests/test_issue_85_streaming.py	Adds integration tests for streaming with subgraphs to verify MESSAGE_COERCION_FAILURE is resolved
tests/test_issue_85_message_coercion.py	Adds unit tests specifically for message coercion and serialization roundtrip scenarios
langgraph/checkpoint/redis/jsonplus_redis.py	Enhances JsonPlusRedisSerializer with comprehensive documentation and improved LangChain object handling
langgraph/checkpoint/redis/base.py	Adds error handling, recovery mechanisms, and detailed logging to message deserialization methods

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}