Update greet function signature to include Command (#1532)

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Co-authored-by: Lauren Hirata Singh <lauren@langchain.dev>

Author: yanglikun

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

@@ -694,7 +694,7 @@ def update_user_info(
 @tool
 def greet(
     runtime: ToolRuntime[CustomContext, CustomState]
-) -> str:
+) -> str | Command:
     """Use this to greet the user once you found their info."""
     user_name = runtime.state.get("user_name", None)
     if user_name is None: