docs(langgraph): add Pramagent tool policy guide

[sriram rampelli (sriram7737)]

Adds a LangGraph production-pattern guide for placing Pramagent at the tool-execution boundary.

Why:

• shows how to validate model-proposed tool calls before side effects execute
• connects ToolGuard decisions to LangGraph interrupts and idempotency guidance
• keeps LangGraph as the orchestration layer and Pramagent as an optional external policy gate

Validation:

• git diff --check

[github-actions]

❌ Import check failed

This PR contains imports from langchain_core that should be imported from langchain instead.

Detailed issues

Analyzing diff for import issues...
 Found 1 import issues:

File: src/oss/langgraph/pramagent-tool-policy.mdx
Line: 74
Issue: Import from langchain.tools instead of langchain_core.tools
Current:   from langchain_core.tools import tool
Suggested: from langchain.tools import tool
--------------------------------------------------------------------------------

 Found 1 import issues that need to be fixed.

Why this is a problem

The langchain package re-exports many modules and classes from langchain_core. When possible, imports should use langchain instead of langchain_core for:

• Better user experience (single import source)
• Consistency across documentation
• Reduced cognitive load for users

How to fix

Replace the imports as suggested above. For example:

• ❌ from langchain_core.messages import HumanMessage
• ✅ from langchain.messages import HumanMessage

🤖 Automated check

This check is based on the latest analysis of langchain re-exports from langchain_core.

[github-actions]

Thanks for opening a docs PR, sriram rampelli (@sriram7737)! When it's ready for review, please add the relevant reviewers:

• @npentrel or @lnhsingh (LangGraph)

[sriram rampelli (sriram7737)]

This is ready for review. Tagging Lauren Hirata Singh (@lnhsingh) for LangGraph review, per the contributor guidance above.