Refactor event loop to use Agent object rather than individual parameters (strands-agents#359)

Update the event_loop_cycle function to accept the agent directly instead of the separate parameters that were coming directly from the agent. This simplifies + clarifies exactly what the event loop is doing with the agent.  Long-term this sets us up for more easily access other agent capabilities like hooks.

There is a downside here of tighter coupling between the agent & the event_loop - an alternative implementation of this would be to abstract the object being passed - maybe something like `EventLoopContext`.  I originally started implementing this approach before revisiting it as it seemed like an unnecessary abstraction.

Author: zastrowm

src/strands/agent/agent.py

@@ -20,10 +20,9 @@
 from opentelemetry import trace
 from pydantic import BaseModel
 
-from ..event_loop.event_loop import event_loop_cycle
+from ..event_loop.event_loop import event_loop_cycle, run_tool
 from ..experimental.hooks import AgentInitializedEvent, EndRequestEvent, HookRegistry, StartRequestEvent
 from ..handlers.callback_handler import PrintingCallbackHandler, null_callback_handler
-from ..handlers.tool_handler import AgentToolHandler
 from ..models.bedrock import BedrockModel
 from ..telemetry.metrics import EventLoopMetrics
 from ..telemetry.tracer import get_tracer
@@ -131,14 +130,7 @@ def caller(
                 }
 
                 # Execute the tool
-                events = self._agent.tool_handler.process(
-                    tool=tool_use,
-                    model=self._agent.model,
-                    system_prompt=self._agent.system_prompt,
-                    messages=self._agent.messages,
-                    tool_config=self._agent.tool_config,
-                    kwargs=kwargs,
-                )
+                events = run_tool(agent=self._agent, tool=tool_use, kwargs=kwargs)
 
                 try:
                     while True:
@@ -292,7 +284,6 @@ def __init__(
         self.load_tools_from_directory = load_tools_from_directory
 
         self.tool_registry = ToolRegistry()
-        self.tool_handler = AgentToolHandler(tool_registry=self.tool_registry)
 
         # Process tool list if provided
         if tools is not None:
@@ -626,14 +617,7 @@ async def _execute_event_loop_cycle(self, kwargs: dict[str, Any]) -> AsyncGenera
         try:
             # Execute the main event loop cycle
             events = event_loop_cycle(
-                model=self.model,
-                system_prompt=self.system_prompt,
-                messages=self.messages,  # will be modified by event_loop_cycle
-                tool_config=self.tool_config,
-                tool_handler=self.tool_handler,
-                thread_pool=self.thread_pool,
-                event_loop_metrics=self.event_loop_metrics,
-                event_loop_parent_span=self.trace_span,
+                agent=self,
                 kwargs=kwargs,
             )
             async for event in events: