Automatic trim / summarization of long conversations

[fjsj]

To avoid errors due to token limit.

See:

• https://langchain-ai.github.io/langgraph/how-tos/memory/manage-conversation-history/
• https://python.langchain.com/docs/how_to/trim_messages/
• https://langchain-ai.github.io/langgraph/concepts/memory/?ref=blog.langchain.dev#summarizing-past-conversations