chore: import upstream snapshot with attribution

examples/integration-langchain/langchain_example.py

@@ -0,0 +1,41 @@
+import os
+import sys
+
+
+def main() -> int:
+    if len(sys.argv) < 2:
+        print(f"Usage: {sys.argv[0]} <question>", file=sys.stderr)
+        return 1
+
+    api_key = os.getenv("OPENAI_API_KEY")
+    if not api_key:
+        print("OPENAI_API_KEY environment variable is required.", file=sys.stderr)
+        return 1
+
+    # Validate CLI inputs before importing optional dependencies so usage and
+    # configuration errors stay concise even before the example is installed.
+    from langchain_core.output_parsers import StrOutputParser
+    from langchain_core.prompts import PromptTemplate
+    from langchain_openai import OpenAI
+
+    llm = OpenAI(temperature=0, api_key=api_key)
+    math_chain = (
+        PromptTemplate.from_template(
+            "Solve the following math problem carefully. Return only the final answer.\n\n{question}"
+        )
+        | llm
+        | StrOutputParser()
+    )
+
+    try:
+        result = math_chain.invoke({"question": sys.argv[1]})
+    except Exception as error:
+        print(f"Error invoking math chain: {error}", file=sys.stderr)
+        return 1
+
+    print(result)
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())