Limit tool calling recursion in agent and address unclear questions

[kdid]

Summary

• Limit the number of tools the agent uses in a turn
• Prompt the agent to ask for clarification on vague questions

Caveats:

• recursion limit is not the number of tool calls per se, it is the number of supersets: https://langchain-ai.github.io/langgraph/how-tos/recursion-limit/, so a limit of 10 equates to roughly 4-5 searches. (not sure if I should set this lower?)
• When the recursion limit is reached, the last 5 messages are retrieved from the checkpointer, summarized and sent as an "answer" to the user. Then the final message is sent.

Steps to test

• Sam sync this branch and ask some complex or vague questions. https://github.com/nulib/dc-api-v2/blob/deploy/prototype/chat/README.md#deploy-a-development-stack
• You can manually adjust the MAX_RECURSION_LIMIT = 10 to lower to make it easier to see how it works in search_agent.py

[mbklein]

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