feat(multiagent): Add __call__ implementation to MultiAgentBase (#645)

Author: mkmeral

src/strands/multiagent/base.py

@@ -3,7 +3,9 @@
 Provides minimal foundation for multi-agent patterns (Swarm, Graph).
 """
 
+import asyncio
 from abc import ABC, abstractmethod
+from concurrent.futures import ThreadPoolExecutor
 from dataclasses import dataclass, field
 from enum import Enum
 from typing import Any, Union
@@ -86,7 +88,12 @@ async def invoke_async(self, task: str | list[ContentBlock], **kwargs: Any) -> M
         """Invoke asynchronously."""
         raise NotImplementedError("invoke_async not implemented")
 
-    @abstractmethod
     def __call__(self, task: str | list[ContentBlock], **kwargs: Any) -> MultiAgentResult:
         """Invoke synchronously."""
-        raise NotImplementedError("__call__ not implemented")
+
+        def execute() -> MultiAgentResult:
+            return asyncio.run(self.invoke_async(task, **kwargs))
+
+        with ThreadPoolExecutor() as executor:
+            future = executor.submit(execute)
+            return future.result()

tests/strands/multiagent/test_base.py

@@ -141,9 +141,35 @@ class CompleteMultiAgent(MultiAgentBase):
         async def invoke_async(self, task: str) -> MultiAgentResult:
             return MultiAgentResult(results={})
 
-        def __call__(self, task: str) -> MultiAgentResult:
-            return MultiAgentResult(results={})
-
-    # Should not raise an exception
+    # Should not raise an exception - __call__ is provided by base class
     agent = CompleteMultiAgent()
     assert isinstance(agent, MultiAgentBase)
+
+
+def test_multi_agent_base_call_method():
+    """Test that __call__ method properly delegates to invoke_async."""
+
+    class TestMultiAgent(MultiAgentBase):
+        def __init__(self):
+            self.invoke_async_called = False
+            self.received_task = None
+            self.received_kwargs = None
+
+        async def invoke_async(self, task, **kwargs):
+            self.invoke_async_called = True
+            self.received_task = task
+            self.received_kwargs = kwargs
+            return MultiAgentResult(
+                status=Status.COMPLETED, results={"test": NodeResult(result=Exception("test"), status=Status.COMPLETED)}
+            )
+
+    agent = TestMultiAgent()
+
+    # Test with string task
+    result = agent("test task", param1="value1", param2="value2")
+
+    assert agent.invoke_async_called
+    assert agent.received_task == "test task"
+    assert agent.received_kwargs == {"param1": "value1", "param2": "value2"}
+    assert isinstance(result, MultiAgentResult)
+    assert result.status == Status.COMPLETED