add cosmos db sample for checkpointer

src/oss/langchain/short-term-memory.mdx

@@ -107,6 +107,40 @@ const checkpointer = PostgresSaver.fromConnString(DB_URI);
 ```
 :::
 
+You can also use Azure Cosmos DB as a checkpoint saver:
+
+:::python
+```shell
+pip install langgraph-checkpoint-cosmosdb
+```
+
+```python
+from langchain.agents import create_agent
+from langgraph_checkpoint_cosmosdb import CosmosDBSaver  # [!code highlight]
+import os
+
+# Set environment variables for authentication
+os.environ["COSMOSDB_ENDPOINT"] = "your_cosmosdb_endpoint"
+os.environ["COSMOSDB_KEY"] = "your_cosmosdb_key"
+
+# Database and Container are created if they don't exist
+checkpointer = CosmosDBSaver(  # [!code highlight]
+    database_name="your_database",  # [!code highlight]
+    container_name="your_container"  # [!code highlight]
+)  # [!code highlight]
+
+agent = create_agent(
+    "gpt-5",
+    [get_user_info],
+    checkpointer=checkpointer,  # [!code highlight]
+)
+```
+
+<Note>
+    Azure Cosmos DB checkpointer supports both sync and async operations. If the database and container already exist, you can use default RBAC credentials (e.g., `az login`) instead of setting the endpoint and key.
+</Note>
+:::
+
 
 ## Customizing agent memory