Fix: enforce strict instructions function signature in get_system_prompt

Author: abdullahimran49

src/agents/agent.py

@@ -393,21 +393,33 @@ async def run_agent(context: RunContextWrapper, input: str) -> str:
         return run_agent
 
     async def get_system_prompt(self, run_context: RunContextWrapper[TContext]) -> str | None:
-        """Get the system prompt for the agent."""
         if isinstance(self.instructions, str):
             return self.instructions
         elif callable(self.instructions):
+            # Inspect the signature of the instructions function
+            sig = inspect.signature(self.instructions)
+            params = list(sig.parameters.values())
+
+            # Enforce exactly 2 parameters
+            if len(params) != 2:
+                raise TypeError(
+                    f"'instructions' callable must accept exactly 2 arguments (context, agent), "
+                    f"but got {len(params)}: {[p.name for p in params]}"
+                )
+
+            # Call the instructions function properly
             if inspect.iscoroutinefunction(self.instructions):
                 return await cast(Awaitable[str], self.instructions(run_context, self))
             else:
                 return cast(str, self.instructions(run_context, self))
+
         elif self.instructions is not None:
-            logger.error(f"Instructions must be a string or a function, got {self.instructions}")
+            logger.error(f"Instructions must be a string or a callable function, got {type(self.instructions).__name__}")
 
         return None
 
     async def get_prompt(
         self, run_context: RunContextWrapper[TContext]
     ) -> ResponsePromptParam | None:
         """Get the prompt for the agent."""
-        return await PromptUtil.to_model_input(self.prompt, run_context, self)
+        return await PromptUtil.to_model_input(self.prompt, run_context, self)

tests/test_agent_instructions_signature.py

@@ -0,0 +1,26 @@
+import pytest
+from src.agents.agent import Agent  # adjust if needed
+
+class DummyContext:
+    pass
+
+class DummyAgent(Agent):
+    def __init__(self, instructions):
+        super().__init__(instructions=instructions)
+
+@pytest.mark.asyncio
+async def test_valid_signature():
+    async def good_instructions(ctx, agent):
+        return "valid"
+    a = DummyAgent(good_instructions)
+    result = await a.get_system_prompt(DummyContext())
+    assert result == "valid"
+
+@pytest.mark.asyncio
+async def test_invalid_signature_raises():
+    async def bad_instructions(ctx):
+        return "invalid"
+    a = DummyAgent(bad_instructions)
+    import pytest
+    with pytest.raises(TypeError):
+        await a.get_system_prompt(DummyContext())