Update agentic-rag.mdx: rewrite_question Node: Role and Content based… (#1334)

… dictionary replaced with LangChain Human Message

As per the docs live officially, in the rewrite_question node, the
response of the model for rewriting the query is returned in dictionary
format to messages in the state.

return {"messages": [{"role": "user", "content": response.content}]}

I understand this has been done keeping in mind to modify the message's
role from ai/assistant to user in the state. While this is not critical
for the time being, it might cause errors while printing graph's
streaming updates.

for node, update in chunk.items():
        print("Update from node", node)
        update["messages"][-1].pretty_print()
        print("\n\n")

This might have been skipped due to running an example where rewrite
node was not required.

However, if the rewrite node comes into play, it would push the
dictionary-based format of messages and not the standard Messages class
format. The pretty print function is valid only on Message classes and
not a dictionary; this would lead to an attribute error: AttributeError:
'dict' object has no attribute 'pretty_print'

For AI learners, especially those who have been exploring LangChain v1.0
docs might get blocked due to this while following the tutorial.

Please merge this one so that it adds to the quality and trust for
LangChain docs.

## Overview
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## Type of change

**Type:** [Replace with: New documentation page / Update existing
documentation / Fix typo/bug/link/formatting / Remove outdated content /
Other]

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## Checklist
<!-- Put an 'x' in all boxes that apply -->
- [ ] I have read the [contributing guidelines](README.md)
- [ ] I have tested my changes locally using `docs dev`
- [x] All code examples have been tested and work correctly
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- [x] I have updated navigation in `src/docs.json` if needed
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## Additional notes
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Author: SrijanShovit225

src/oss/langgraph/agentic-rag.mdx

@@ -523,6 +523,8 @@ Note that the components will operate on the [`MessagesState`](/oss/langgraph/gr
 :::python
 1. Build the `rewrite_question` node. The retriever tool can return potentially irrelevant documents, which indicates a need to improve the original user question. To do so, we will call the `rewrite_question` node:
   ```python
+  from langchain.messages import HumanMessage
+
   REWRITE_PROMPT = (
       "Look at the input and try to reason about the underlying semantic intent / meaning.\n"
       "Here is the initial question:"
@@ -539,7 +541,7 @@ Note that the components will operate on the [`MessagesState`](/oss/langgraph/gr
       question = messages[0].content
       prompt = REWRITE_PROMPT.format(question=question)
       response = response_model.invoke([{"role": "user", "content": prompt}])
-      return {"messages": [{"role": "user", "content": response.content}]}
+      return {"messages": [HumanMessage(content=response.content)]}
   ```
 2. Try it out:
   ```python
@@ -567,7 +569,7 @@ Note that the components will operate on the [`MessagesState`](/oss/langgraph/gr
   }
 
   response = rewrite_question(input)
-  print(response["messages"][-1]["content"])
+  print(response["messages"][-1].content)
   ```
   **Output:**
   ```