Identify parent_flow of Crew and LiteAgent (#2723)

This commit adds a new crew field called parent_flow, evaluated when the Crew
instance is instantiated. The stacktrace is traversed to look up if the caller
is an instance of Flow, and if so, it fills in the field.

Other alternatives were considered, such as a global context or even a new
field to be manually filled, however, this is the most magical solution that
was thread-safe and did not require public API changes.

tests/test_lite_agent.py

@@ -1,13 +1,16 @@
 import asyncio
 from typing import cast
+from unittest.mock import Mock
 
 import pytest
 from pydantic import BaseModel, Field
 
 from crewai import LLM, Agent
+from crewai.flow import Flow, start
 from crewai.lite_agent import LiteAgent, LiteAgentOutput
 from crewai.tools import BaseTool
 from crewai.utilities.events import crewai_event_bus
+from crewai.utilities.events.agent_events import LiteAgentExecutionStartedEvent
 from crewai.utilities.events.tool_usage_events import ToolUsageStartedEvent
 
 
@@ -255,3 +258,60 @@ async def test_lite_agent_returns_usage_metrics_async():
     assert "21 million" in result.raw or "37 million" in result.raw
     assert result.usage_metrics is not None
     assert result.usage_metrics["total_tokens"] > 0
+
+
+class TestFlow(Flow):
+    """A test flow that creates and runs an agent."""
+
+    def __init__(self, llm, tools):
+        self.llm = llm
+        self.tools = tools
+        super().__init__()
+
+    @start()
+    def start(self):
+        agent = Agent(
+            role="Test Agent",
+            goal="Test Goal",
+            backstory="Test Backstory",
+            llm=self.llm,
+            tools=self.tools,
+        )
+        return agent.kickoff("Test query")
+
+
+def verify_agent_parent_flow(result, agent, flow):
+    """Verify that both the result and agent have the correct parent flow."""
+    assert result.parent_flow is flow
+    assert agent is not None
+    assert agent.parent_flow is flow
+
+
+def test_sets_parent_flow_when_inside_flow():
+    captured_agent = None
+
+    mock_llm = Mock(spec=LLM)
+    mock_llm.call.return_value = "Test response"
+
+    class MyFlow(Flow):
+        @start()
+        def start(self):
+            agent = Agent(
+                role="Test Agent",
+                goal="Test Goal",
+                backstory="Test Backstory",
+                llm=mock_llm,
+                tools=[WebSearchTool()],
+            )
+            return agent.kickoff("Test query")
+
+    flow = MyFlow()
+    with crewai_event_bus.scoped_handlers():
+
+        @crewai_event_bus.on(LiteAgentExecutionStartedEvent)
+        def capture_agent(source, event):
+            nonlocal captured_agent
+            captured_agent = source
+
+        result = flow.kickoff()
+        assert captured_agent.parent_flow is flow