feat: implement hierarchical agent delegation with allowed_agents parameter

- Add allowed_agents parameter to BaseAgent
- Add validation for allowed_agents list
- Update delegation tools to respect restrictions
- Add error messages for unauthorized delegation
- Add tests for hierarchical delegation

Co-Authored-By: Joe Moura <joao@crewai.com>

tests/agents/test_delegation.py

@@ -0,0 +1,166 @@
+import pytest
+from unittest.mock import MagicMock
+
+from crewai.agent import Agent
+from crewai.crew import Crew
+from crewai.task import Task
+from crewai.tools.agent_tools.delegate_work_tool import DelegateWorkTool
+
+def test_delegate_work_with_allowed_agents():
+    """Test successful delegation to allowed agent."""
+    # Create agents
+    executive = Agent(
+        role="Executive Director",
+        goal="Manage the team",
+        backstory="An experienced manager",
+        allow_delegation=True,
+        allowed_agents=["Communications Manager"]
+    )
+    comms_manager = Agent(
+        role="Communications Manager",
+        goal="Handle communications",
+        backstory="A skilled communicator",
+        allow_delegation=False
+    )
+    
+    # Mock LLM to avoid actual API calls
+    mock_content = "Thought: I will handle this task\nFinal Answer: Task completed successfully"
+    mock_response = {
+        "choices": [{
+            "message": {
+                "content": mock_content
+            }
+        }]
+    }
+    executive.llm = MagicMock()
+    executive.llm.invoke = MagicMock(return_value=mock_response)
+    executive.llm.call = MagicMock(return_value=mock_content)
+    comms_manager.llm = MagicMock()
+    comms_manager.llm.invoke = MagicMock(return_value=mock_response)
+    comms_manager.llm.call = MagicMock(return_value=mock_content)
+    
+    # Create crew and tool
+    crew = Crew(agents=[executive, comms_manager])
+    tool = DelegateWorkTool(
+        name="Delegate work to coworker",
+        description="Tool for delegating work to coworkers",
+        agents=[executive, comms_manager],
+        agent_id=executive.id
+    )
+    
+    # Test delegation
+    result = tool._execute(
+        agent_name="Communications Manager",
+        task="Write a press release",
+        context="Important company announcement"
+    )
+    
+    # Verify delegation was allowed
+    assert "error" not in result.lower()
+    assert "unauthorized" not in result.lower()
+
+def test_delegate_work_with_unauthorized_agent():
+    """Test failed delegation to unauthorized agent."""
+    # Create agents
+    executive = Agent(
+        role="Executive Director",
+        goal="Manage the team",
+        backstory="An experienced manager",
+        allow_delegation=True,
+        allowed_agents=["Communications Manager"]
+    )
+    tech_manager = Agent(
+        role="Tech Manager",
+        goal="Manage technology",
+        backstory="A tech expert",
+        allow_delegation=False
+    )
+    
+    # Mock LLM to avoid actual API calls
+    mock_content = "Thought: I will handle this task\nFinal Answer: Task completed successfully"
+    mock_response = {
+        "choices": [{
+            "message": {
+                "content": mock_content
+            }
+        }]
+    }
+    executive.llm = MagicMock()
+    executive.llm.invoke = MagicMock(return_value=mock_response)
+    executive.llm.call = MagicMock(return_value=mock_content)
+    tech_manager.llm = MagicMock()
+    tech_manager.llm.invoke = MagicMock(return_value=mock_response)
+    tech_manager.llm.call = MagicMock(return_value=mock_content)
+    
+    # Create crew and tool
+    crew = Crew(agents=[executive, tech_manager])
+    tool = DelegateWorkTool(
+        name="Delegate work to coworker",
+        description="Tool for delegating work to coworkers",
+        agents=[executive, tech_manager],
+        agent_id=executive.id
+    )
+    
+    # Test delegation
+    result = tool._execute(
+        agent_name="Tech Manager",
+        task="Update servers",
+        context="Server maintenance needed"
+    )
+    
+    # Verify delegation was blocked with proper error message
+    assert "cannot delegate this task" in result.lower()
+    assert "tech manager" in result.lower()
+    assert "communications manager" in result.lower()
+
+def test_delegate_work_without_allowed_agents():
+    """Test delegation works normally when no allowed_agents is specified."""
+    # Create agents
+    manager = Agent(
+        role="Manager",
+        goal="Manage the team",
+        backstory="An experienced manager",
+        allow_delegation=True  # No allowed_agents specified
+    )
+    worker = Agent(
+        role="Worker",
+        goal="Do the work",
+        backstory="A skilled worker",
+        allow_delegation=False
+    )
+    
+    # Mock LLM to avoid actual API calls
+    mock_content = "Thought: I will handle this task\nFinal Answer: Task completed successfully"
+    mock_response = {
+        "choices": [{
+            "message": {
+                "content": mock_content
+            }
+        }]
+    }
+    manager.llm = MagicMock()
+    manager.llm.invoke = MagicMock(return_value=mock_response)
+    manager.llm.call = MagicMock(return_value=mock_content)
+    worker.llm = MagicMock()
+    worker.llm.invoke = MagicMock(return_value=mock_response)
+    worker.llm.call = MagicMock(return_value=mock_content)
+    
+    # Create crew and tool
+    crew = Crew(agents=[manager, worker])
+    tool = DelegateWorkTool(
+        name="Delegate work to coworker",
+        description="Tool for delegating work to coworkers",
+        agents=[manager, worker],
+        agent_id=manager.id
+    )
+    
+    # Test delegation
+    result = tool._execute(
+        agent_name="Worker",
+        task="Complete task",
+        context="Important task"
+    )
+    
+    # Verify delegation was allowed
+    assert "error" not in result.lower()
+    assert "unauthorized" not in result.lower()