Fix empty agent response in ADK agent when tools are used

src/mcprobe/agents/adk.py

@@ -134,8 +134,9 @@ async def send_message(self, message: str) -> AgentResponse:
                         self._process_function_responses(responses, pending_calls)
                     )
 
-                # Get final response text
-                if event.is_final_response() and event.content and event.content.parts:
+                # Capture text from any event with text content
+                # (not just final response - text may come in earlier events when tools are used)
+                if event.content and event.content.parts:
                     for part in event.content.parts:
                         if hasattr(part, "text") and part.text:
                             response_text += part.text

src/mcprobe/synthetic_user/user.py

@@ -62,6 +62,13 @@ async def respond(self, assistant_message: str) -> UserResponse:
         Raises:
             OrchestrationError: If the LLM call fails.
         """
+        # Handle empty agent responses - ask for clarification instead of confusing the LLM
+        if not assistant_message.strip():
+            response = "I didn't receive a response. Could you try again?"
+            self._conversation_history.append(Message(role="assistant", content=assistant_message))
+            self._conversation_history.append(Message(role="user", content=response))
+            return UserResponse(message=response, tokens_used=0)
+
         # Add assistant message to history
         self._conversation_history.append(Message(role="assistant", content=assistant_message))
 

tests/unit/test_synthetic_user.py

@@ -129,3 +129,39 @@ async def test_tokens_default_to_zero_on_missing_usage(
         response = await user.respond("Hello")
 
         assert response.tokens_used == 0
+
+    @pytest.mark.asyncio
+    async def test_empty_agent_response_asks_for_retry(
+        self,
+        mock_provider: LLMProvider,
+        user_config: SyntheticUserConfig,
+    ) -> None:
+        """Test that empty agent responses result in clarification request."""
+        user = SyntheticUserLLM(mock_provider, user_config)
+
+        # Agent sends empty response
+        response = await user.respond("")
+
+        # Synthetic user asks for retry instead of calling LLM
+        assert response.message == "I didn't receive a response. Could you try again?"
+        assert response.tokens_used == 0
+
+        # LLM should NOT have been called
+        mock_provider.generate.assert_not_called()
+
+    @pytest.mark.asyncio
+    async def test_whitespace_only_agent_response_asks_for_retry(
+        self,
+        mock_provider: LLMProvider,
+        user_config: SyntheticUserConfig,
+    ) -> None:
+        """Test that whitespace-only agent responses result in clarification request."""
+        user = SyntheticUserLLM(mock_provider, user_config)
+
+        # Agent sends whitespace-only response
+        response = await user.respond("   \n\t  ")
+
+        # Synthetic user asks for retry
+        assert response.message == "I didn't receive a response. Could you try again?"
+        assert response.tokens_used == 0
+        mock_provider.generate.assert_not_called()