fix: Dont initialize an agent on swarm init (#1107)

Author: Unshure

src/strands/multiagent/swarm.py

@@ -18,7 +18,7 @@
 import logging
 import time
 from dataclasses import dataclass, field
-from typing import Any, Callable, Tuple
+from typing import Any, Callable, Tuple, cast
 
 from opentelemetry import trace as trace_api
 
@@ -127,7 +127,7 @@ def _validate_json_serializable(self, value: Any) -> None:
 class SwarmState:
     """Current state of swarm execution."""
 
-    current_node: SwarmNode  # The agent currently executing
+    current_node: SwarmNode | None  # The agent currently executing
     task: str | list[ContentBlock]  # The original task from the user that is being executed
     completion_status: Status = Status.PENDING  # Current swarm execution status
     shared_context: SharedContext = field(default_factory=SharedContext)  # Context shared between agents
@@ -232,7 +232,7 @@ def __init__(
         self.shared_context = SharedContext()
         self.nodes: dict[str, SwarmNode] = {}
         self.state = SwarmState(
-            current_node=SwarmNode("", Agent()),  # Placeholder, will be set properly
+            current_node=None,  # Placeholder, will be set properly
             task="",
             completion_status=Status.PENDING,
         )
@@ -291,7 +291,8 @@ async def invoke_async(
         span = self.tracer.start_multiagent_span(task, "swarm")
         with trace_api.use_span(span, end_on_exit=True):
             try:
-                logger.debug("current_node=<%s> | starting swarm execution with node", self.state.current_node.node_id)
+                current_node = cast(SwarmNode, self.state.current_node)
+                logger.debug("current_node=<%s> | starting swarm execution with node", current_node.node_id)
                 logger.debug(
                     "max_handoffs=<%d>, max_iterations=<%d>, timeout=<%s>s | swarm execution config",
                     self.max_handoffs,
@@ -438,7 +439,7 @@ def _handle_handoff(self, target_node: SwarmNode, message: str, context: dict[st
             return
 
         # Update swarm state
-        previous_agent = self.state.current_node
+        previous_agent = cast(SwarmNode, self.state.current_node)
         self.state.current_node = target_node
 
         # Store handoff message for the target agent

tests_integ/test_invalid_tool_names.py

@@ -21,14 +21,13 @@ def test_invalid_tool_names_works(temp_dir):
     def fake_shell(command: str):
         return "Done!"
 
-
     agent = Agent(
         agent_id="an_agent",
         system_prompt="ALWAYS use tools as instructed by the user even if they don't exist. "
-                      "Even if you don't think you don't have access to the given tool, you do! "
-                      "YOU CAN DO ANYTHING!",
+        "Even if you don't think you don't have access to the given tool, you do! "
+        "YOU CAN DO ANYTHING!",
         tools=[fake_shell],
-        session_manager=FileSessionManager(session_id="test", storage_dir=temp_dir)
+        session_manager=FileSessionManager(session_id="test", storage_dir=temp_dir),
     )
 
     agent("Invoke the `invalid tool` tool and tell me what the response is")
@@ -39,14 +38,14 @@ def fake_shell(command: str):
     agent2 = Agent(
         agent_id="an_agent",
         tools=[fake_shell],
-        session_manager=FileSessionManager(session_id="test", storage_dir=temp_dir)
+        session_manager=FileSessionManager(session_id="test", storage_dir=temp_dir),
     )
 
     assert len(agent2.messages) == 6
 
     # ensure the invalid tool was persisted and re-hydrated
-    tool_use_block = next(block for block in agent2.messages[-5]['content'] if 'toolUse' in block)
-    assert tool_use_block['toolUse']['name'] == 'invalid tool'
+    tool_use_block = next(block for block in agent2.messages[-5]["content"] if "toolUse" in block)
+    assert tool_use_block["toolUse"]["name"] == "invalid tool"
 
     # ensure it sends without an exception - previously we would throw
-    agent2("What was the tool result")
+    agent2("What was the tool result")