conversation manager - summarization - noop tool (#1003)

Author: pgrayy

src/strands/agent/conversation_manager/summarizing_conversation_manager.py

@@ -5,6 +5,8 @@
 
 from typing_extensions import override
 
+from ...tools import tool
+from ...tools.registry import ToolRegistry
 from ...types.content import Message
 from ...types.exceptions import ContextWindowOverflowException
 from .conversation_manager import ConversationManager
@@ -23,6 +25,10 @@
 - You MUST create a structured and concise summary in bullet-point format.
 - You MUST NOT respond conversationally.
 - You MUST NOT address the user directly.
+- You MUST NOT comment on tool availability.
+
+Assumptions:
+- You MUST NOT assume tool executions failed unless otherwise stated.
 
 Task:
 Your task is to create a structured summary document:
@@ -182,9 +188,10 @@ def _generate_summary(self, messages: List[Message], agent: "Agent") -> Message:
         # Choose which agent to use for summarization
         summarization_agent = self.summarization_agent if self.summarization_agent is not None else agent
 
-        # Save original system prompt and messages to restore later
+        # Save original system prompt, messages, and tool registry to restore later
         original_system_prompt = summarization_agent.system_prompt
         original_messages = summarization_agent.messages.copy()
+        original_tool_registry = summarization_agent.tool_registry
 
         try:
             # Only override system prompt if no agent was provided during initialization
@@ -197,6 +204,13 @@ def _generate_summary(self, messages: List[Message], agent: "Agent") -> Message:
                 )
                 # Temporarily set the system prompt for summarization
                 summarization_agent.system_prompt = system_prompt
+
+            # Add no-op tool if agent has no tools to satisfy tool spec requirement
+            if not summarization_agent.tool_names:
+                tool_registry = ToolRegistry()
+                tool_registry.register_tool(self._noop_tool)
+                summarization_agent.tool_registry = tool_registry
+
             summarization_agent.messages = messages
 
             # Use the agent to generate summary with rich content (can use tools if needed)
@@ -207,6 +221,7 @@ def _generate_summary(self, messages: List[Message], agent: "Agent") -> Message:
             # Restore original agent state
             summarization_agent.system_prompt = original_system_prompt
             summarization_agent.messages = original_messages
+            summarization_agent.tool_registry = original_tool_registry
 
     def _adjust_split_point_for_tool_pairs(self, messages: List[Message], split_point: int) -> int:
         """Adjust the split point to avoid breaking ToolUse/ToolResult pairs.
@@ -249,3 +264,13 @@ def _adjust_split_point_for_tool_pairs(self, messages: List[Message], split_poin
             raise ContextWindowOverflowException("Unable to trim conversation context!")
 
         return split_point
+
+    @tool(name="noop", description="MUST NOT call or summarize")
+    def _noop_tool(self) -> None:
+        """No-op tool to satisfy tool spec requirement when tool messages are present.
+
+        Some model provides (e.g., Bedrock) will return an error response if tool uses and tool results are present in
+        messages without any tool specs configured. Consequently, if the summarization agent has no registered tools,
+        summarization will fail. As a workaround, we register the no-op tool.
+        """
+        pass

tests/strands/agent/test_summarizing_conversation_manager.py

@@ -19,6 +19,8 @@ def __init__(self, summary_response="This is a summary of the conversation."):
         self.messages = []
         self.model = Mock()
         self.call_tracker = Mock()
+        self.tool_registry = Mock()
+        self.tool_names = []
 
     def __call__(self, prompt):
         """Mock agent call that returns a summary."""
@@ -608,3 +610,30 @@ def test_summarizing_conversation_manager_properly_records_removed_message_count
     # so we dont count this toward the total:
     # 4 (Previously removed messages) + 2 (removed messages) - 1 (Previous summary message) = 5
     assert manager.removed_message_count == 5
+
+
+@patch("strands.agent.conversation_manager.summarizing_conversation_manager.ToolRegistry")
+def test_summarizing_conversation_manager_generate_summary_with_noop_tool(mock_registry_cls, summarizing_manager):
+    mock_registry = mock_registry_cls.return_value
+
+    messages = [{"role": "user", "content": [{"text": "test"}]}]
+    agent = create_mock_agent()
+
+    original_tool_registry = agent.tool_registry
+    summarizing_manager._generate_summary(messages, agent)
+
+    assert original_tool_registry == agent.tool_registry
+    mock_registry.register_tool.assert_called_once()
+
+
+@patch("strands.agent.conversation_manager.summarizing_conversation_manager.ToolRegistry")
+def test_summarizing_conversation_manager_generate_summary_with_tools(mock_registry_cls, summarizing_manager):
+    mock_registry = mock_registry_cls.return_value
+
+    messages = [{"role": "user", "content": [{"text": "test"}]}]
+    agent = create_mock_agent()
+    agent.tool_names = ["test_tool"]
+
+    summarizing_manager._generate_summary(messages, agent)
+
+    mock_registry.register_tool.assert_not_called()

tests_integ/test_summarizing_conversation_manager_integration.py

@@ -372,3 +372,39 @@ def test_dedicated_summarization_agent(model, summarization_model):
             break
 
     assert summary_text
+
+
+def test_summarization_with_tool_messages_and_no_tools():
+    agent = Agent(
+        messages=[
+            {"role": "user", "content": [{"text": "What is the current time?"}]},
+            {
+                "role": "assistant",
+                "content": [{"toolUse": {"toolUseId": "t1", "name": "time_tool", "input": {}}}],
+            },
+            {
+                "role": "user",
+                "content": [
+                    {
+                        "toolResult": {
+                            "toolUseId": "t1",
+                            "content": [{"text": "12:00"}],
+                            "status": "success",
+                        }
+                    }
+                ],
+            },
+            {"role": "assistant", "content": [{"text": "The current time is 12:00."}]},
+            {"role": "user", "content": [{"text": "Thank you"}]},
+            {"role": "assistant", "content": [{"text": "You are welcome."}]},
+        ],
+    )
+
+    conversation_manager = SummarizingConversationManager(summary_ratio=1, preserve_recent_messages=2)
+    conversation_manager.reduce_context(agent)
+
+    assert len(agent.tool_names) == 0
+    assert len(agent.messages) == 3
+
+    summary = str(agent.messages[0]).lower()
+    assert "12:00" in summary