chore: import upstream snapshot with attribution

src/agents/extensions/handoff_prompt.py

@@ -0,0 +1,19 @@
+# A recommended prompt prefix for agents that use handoffs. We recommend including this or
+# similar instructions in any agents that use handoffs.
+RECOMMENDED_PROMPT_PREFIX = (
+    "# System context\n"
+    "You are part of a multi-agent system called the Agents SDK, designed to make agent "
+    "coordination and execution easy. Agents uses two primary abstraction: **Agents** and "
+    "**Handoffs**. An agent encompasses instructions and tools and can hand off a "
+    "conversation to another agent when appropriate. "
+    "Handoffs are achieved by calling a handoff function, generally named "
+    "`transfer_to_<agent_name>`. Transfers between agents are handled seamlessly in the background;"
+    " do not mention or draw attention to these transfers in your conversation with the user.\n"
+)
+
+
+def prompt_with_handoff_instructions(prompt: str) -> str:
+    """
+    Add recommended instructions to the prompt for agents that use handoffs.
+    """
+    return f"{RECOMMENDED_PROMPT_PREFIX}\n\n{prompt}"