fix: Don't bail out if there are no tool_uses (strands-agents#1087)

Partial fix to strands-agents#1069 - previously the agent would prematurely exit if the agent generated a tool with an invalid name; this avoids that by ensuring the agent loop continues with zero tool-uses.

---------

Co-authored-by: Mackenzie Zastrow <[email protected]>

Author: zastrowm

src/strands/event_loop/event_loop.py

@@ -427,9 +427,6 @@ async def _handle_tool_execution(
 
     validate_and_prepare_tools(message, tool_uses, tool_results, invalid_tool_use_ids)
     tool_uses = [tool_use for tool_use in tool_uses if tool_use.get("toolUseId") not in invalid_tool_use_ids]
-    if not tool_uses:
-        yield EventLoopStopEvent(stop_reason, message, agent.event_loop_metrics, invocation_state["request_state"])
-        return
 
     if agent._interrupt_state.activated:
         tool_results.extend(agent._interrupt_state.context["tool_results"])

tests/fixtures/mocked_model_provider.py

@@ -1,5 +1,5 @@
 import json
-from typing import Any, AsyncGenerator, Iterable, Optional, Type, TypedDict, TypeVar, Union
+from typing import Any, AsyncGenerator, Iterable, Optional, Sequence, Type, TypedDict, TypeVar, Union
 
 from pydantic import BaseModel
 
@@ -25,8 +25,8 @@ class MockedModelProvider(Model):
     to stream mock responses as events.
     """
 
-    def __init__(self, agent_responses: list[Union[Message, RedactionMessage]]):
-        self.agent_responses = agent_responses
+    def __init__(self, agent_responses: Sequence[Union[Message, RedactionMessage]]):
+        self.agent_responses = [*agent_responses]
         self.index = 0
 
     def format_chunk(self, event: Any) -> StreamEvent:

tests/strands/agent/test_agent.py

@@ -2065,3 +2065,50 @@ def test_agent_tool_caller_interrupt(user):
     exp_message = r"cannot directly call tool during interrupt"
     with pytest.raises(RuntimeError, match=exp_message):
         agent.tool.test_tool()
+
+
+def test_agent__call__invalid_tool_name():
+    @strands.tool
+    def shell(command: str):
+        pass
+
+    model = MockedModelProvider(
+        [
+            {
+                "role": "assistant",
+                "content": [
+                    {
+                        "toolUse": {
+                            "toolUseId": "tool_use_id",
+                            "name": "invalid tool",
+                            "input": "{}",
+                        }
+                    }
+                ],
+            },
+            {"role": "assistant", "content": [{"text": "I invoked a tool!"}]},
+        ]
+    )
+
+    agent = Agent(tools=[shell], model=model)
+    result = agent("Test")
+
+    # Ensure the stop_reason is
+    assert result.stop_reason == "end_turn"
+
+    # Assert that there exists a message with a toolResponse
+    assert agent.messages[-2] == {
+        "content": [
+            {
+                "toolResult": {
+                    "content": [{"text": "Error: tool_name=<invalid tool> | invalid tool name pattern"}],
+                    "status": "error",
+                    "toolUseId": "tool_use_id",
+                }
+            }
+        ],
+        "role": "user",
+    }
+
+    # And that it continued to the LLM call
+    assert agent.messages[-1] == {"content": [{"text": "I invoked a tool!"}], "role": "assistant"}

tests/strands/event_loop/test_event_loop.py

@@ -1,6 +1,6 @@
 import concurrent
 import unittest.mock
-from unittest.mock import MagicMock, call, patch
+from unittest.mock import ANY, MagicMock, call, patch
 
 import pytest
 
@@ -18,13 +18,15 @@
 from strands.telemetry.metrics import EventLoopMetrics
 from strands.tools.executors import SequentialToolExecutor
 from strands.tools.registry import ToolRegistry
+from strands.types._events import EventLoopStopEvent
 from strands.types.exceptions import (
     ContextWindowOverflowException,
     EventLoopException,
     MaxTokensReachedException,
     ModelThrottledException,
 )
 from tests.fixtures.mock_hook_provider import MockHookProvider
+from tests.fixtures.mocked_model_provider import MockedModelProvider
 
 
 @pytest.fixture
@@ -744,6 +746,8 @@ async def test_event_loop_cycle_with_parent_span(
 async def test_request_state_initialization(alist):
     # Create a mock agent
     mock_agent = MagicMock()
+    # not setting this to False results in endless recursion
+    mock_agent._interrupt_state.activated = False
     mock_agent.event_loop_metrics.start_cycle.return_value = (0, MagicMock())
 
     # Call without providing request_state
@@ -1011,3 +1015,52 @@ def interrupt_callback(event):
         "interrupts": {},
     }
     assert tru_state == exp_state
+
+
+@pytest.mark.asyncio
+async def test_invalid_tool_names_adds_tool_uses(agent, model, alist):
+    model.stream = MockedModelProvider(
+        [
+            {
+                "role": "assistant",
+                "content": [
+                    {
+                        "toolUse": {
+                            "toolUseId": "tool_use_id",
+                            "name": "invalid tool",
+                            "input": "{}",
+                        }
+                    }
+                ],
+            },
+            {"role": "assistant", "content": [{"text": "I invoked a tool!"}]},
+        ]
+    ).stream
+
+    stream = strands.event_loop.event_loop.event_loop_cycle(
+        agent=agent,
+        invocation_state={},
+    )
+    events = await alist(stream)
+
+    # ensure that we got end_turn and not tool_use
+    assert events[-1] == EventLoopStopEvent(
+        stop_reason="end_turn",
+        message={"content": [{"text": "I invoked a tool!"}], "role": "assistant"},
+        metrics=ANY,
+        request_state={},
+    )
+
+    # Ensure that an "invalid tool name" message was added properly
+    assert agent.messages[-2] == {
+        "content": [
+            {
+                "toolResult": {
+                    "content": [{"text": "Error: tool_name=<invalid tool> | invalid tool name pattern"}],
+                    "status": "error",
+                    "toolUseId": "tool_use_id",
+                }
+            }
+        ],
+        "role": "user",
+    }