Add example for configuring an anonymizer for LangGraph (#607)

## Overview
Show how to set up an anonymizer with LangGraph to redact sensitive
data.

## Type of change

**Type:** Other

## Checklist
<!-- Put an 'x' in all boxes that apply -->
- [x] I have read the [contributing guidelines](README.md)
- [x] I have tested my changes locally using `docs dev`
- [x] All code examples have been tested and work correctly
- [x] I have used **root relative** paths for internal links
- [ ] I have updated navigation in `src/docs.json` if needed
- [ ] I have gotten approval from the relevant reviewers
- [ ] (Internal team members only / optional) I have created a preview
deployment using the [Create Preview Branch
workflow](https://github.com/langchain-ai/docs/actions/workflows/create-preview-branch.yml)

## Additional notes
<!-- Any other information that would be helpful for reviewers -->

---------

Co-authored-by: Lauren Hirata Singh <[email protected]>

Author: rahul-langchain

src/oss/langgraph/observability.mdx

@@ -30,6 +30,61 @@ export LANGSMITH_API_KEY=<your-api-key>
 
 By default, the trace will be logged to the project with the name `default`. To configure a custom project name, see [Log to a project](#log-to-a-project).
 
-For more information, see [Trace with LangGraph](langsmith/trace-with-langgraph).
+For more information, see [Trace with LangGraph](/langsmith/trace-with-langgraph).
 
 <observability />
+
+## Use anonymizers to prevent logging of sensitive data in traces
+
+You may want to mask sensitive data to prevent it from being logged to LangSmith. You can create [anonymizers](/langsmith/mask-inputs-outputs#rule-based-masking-of-inputs-and-outputs) and apply them to
+your graph using configuration. This example will redact anything matching the Social Security Number format XXX-XX-XXXX from traces sent to LangSmith.
+
+:::python
+```python Python
+from langchain_core.tracers.langchain import LangChainTracer
+from langgraph.graph import StateGraph, MessagesState
+from langsmith import Client
+from langsmith.anonymizer import create_anonymizer
+
+anonymizer = create_anonymizer([
+    # Matches SSNs
+    { "pattern": r"\b\d{3}-?\d{2}-?\d{4}\b", "replace": "<ssn>" }
+])
+
+tracer_client = Client(anonymizer=anonymizer)
+tracer = LangChainTracer(client=tracer_client)
+# Define the graph
+graph = (
+    StateGraph(MessagesState)
+    ...
+    .compile()
+    .with_config({'callbacks': [tracer]})
+)
+```
+:::
+:::js
+```typescript TypeScript
+import { StateGraph } from "@langchain/langgraph";
+import { LangChainTracer } from "@langchain/core/tracers/tracer_langchain";
+import { StateAnnotation } from "./state.js";
+import { createAnonymizer } from "langsmith/anonymizer"
+import { Client } from "langsmith"
+
+
+const anonymizer = createAnonymizer([
+    # Matches SSNs
+    { pattern: /\b\d{3}-?\d{2}-?\d{4}\b/, replace: "<ssn>" }
+])
+
+const langsmithClient = new Client({ anonymizer })
+const tracer = new LangChainTracer({
+  client: langsmithClient,
+});
+
+export const graph = new StateGraph(StateAnnotation)
+  .compile()
+  .withConfig({
+    callbacks: [tracer],
+});
+```
+:::