fix AI-163
fix AI-164
<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit
- **Tests**
- Added a new test to verify multi-turn chat interactions, ensuring accurate handling of chat history and correct responses for translation and explanation requests.
- **Bug Fixes**
- Improved chat session logic to better merge user messages and attachments, enhancing the accuracy and continuity of multi-step conversations.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->